Greenland's ice sheet is melting six times faster than it was in the 1980s. And all that meltwater is directly raising sea levels.

That's all according to a new study, published yesterday (April 22) in the journal Proceedings of the National Academy of Sciences, that carefully reconstructs the behavior of the ice sheet in the decades before modern measurement tools became available. Scientists already knew that there was a lot more ice on Greenland in the 1970s and 1980s. And they've had precise measurements of the increase in melting since the 1990s. Now they know just how dramatically things have changed in the last 46 years.

"When you look at several decades, it is best to sit back in your chair before looking at the results, because it is a bit scary to see how fast it is changing," University of California, Irvine, glaciologist Eric Rignot, a co-author of the study, said in a statement. [Image Gallery: Greenland's Melting Glaciers]

Greenland is just one island. But its ice sheet has the potential to transform the entire planet. The Greenland ice sheet has existed for 2.4 million years and is 2.1 miles (3.4 kilometers) thick at its deepest point. The whole thing weighs about half as much as Earth's whole atmosphere, or 6 quintillion — or 6 with 18 zeros after it — lbs. (2.7 quintillion kilograms). If it melted entirely, sea levels would rise by 24.3 feet (7.4 meters).

In the 21st century, scientists use laser measurements of the height of the ice, measurements of the ice sheet's total gravity and satellite photos to gauge changes in ice thickness. That's how they know that the sheet is melting four times faster now than it was in 2003, as Live Science previously reported.

To extend that record further into the past, the researchers divided Greenland into 260 "basins" of ice, which they studied individually using a combination of direct measurements of ice changes in satellite photos and sophisticated computer models of ice behavior. They found that between 1972 and 1980, Greenland actually gained roughly 100 trillion lbs. (47 trillion kg) of ice per year. The real mass loss, they found, started in the 1980s. Between 1980 and 1990, the island lost in the ballpark of 112 trillion lbs. (51 trillion kg) of ice per year. Between 1990 and 2000, it lost about 90 trillion lbs. (41 trillion kg) per year.

Then, in the 2000s, things dramatically accelerated.

Between 2000 and 2010, Greenland lost about 412 trillion lbs. (187 trillion kg) of ice per year. Between 2010 and 2018, the ice sheet lost roughly 631 trillion lbs. (286 trillion kilograms) of ice per year.

Those numbers make concrete what researchers and inhabitants of Greenland already knew: that the island is changing and its ancient glaciers are receding at an alarming rate. The dramatic uptick in ice loss in the last two decades coincides with a similar surge in atmospheric greenhouse gases and warming. As Live Science reported earlier this year, nine of the 10 warmest winters on record have happened since 2005.

What does this all mean for the future of the ice sheet, as well as global sea levels? As the Intergovernmental Panel on Climate Change concluded, that will depend primarily on what humans do next.

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Originally published on Live Science.

SAN FRANCISCO — The world may have just turned the corner in the battle against climate change, former U.S. Vice President Al Gore says.

The Paris agreement, which 195 nations signed over the weekend, could be the breakthrough that lets humanity avoid a looming climate catastrophe, Gore said here Wednesday (Dec. 16) at the annual fall meeting of the American Geophysical Union.

The plan of action laid out by the accord, "while far from ideal, nevertheless sets in motion a process of change that gives us an excellent chance of accelerating the measures that could actually bring us to a point where we can start stabilizing the climate," Gore said. [The Reality of Climate Change: 10 Myths Busted]

The Paris treaty's signatory nations — which include the United States and China, the two largest emitters of heat-trapping carbon dioxide(CO2) — agreed to cut greenhouse-gas emissions, and to set more ambitious reduction targets every five years. (The agreement does not prescribe exactly how steep these cuts must be and does not impose sanctions on countries that fail to meet the ambitious objectives.)

The overall goal is to keep average global temperatures from rising more than 3.6 degrees Fahrenheit (2 degrees Celsius) above pre-industrial levels — and ideally, to prevent this warming from topping 2.7 degrees F (1.5 degrees C).

The Paris pact by itself is no silver bullet, experts have said. But it should help foster an environment in which climate stabilization is possible, especially when combined with economic factors such as the ever-falling price of solar power and other renewable energy sources, Gore said Wednesday.

"The signal sent to the business community and the investor community, along with civil society, is very, very powerful, and we're already getting feedback that the message is being received very powerfully," he said, calling the Paris deal "a great success."

Still, the struggle against human-caused climate change is far from over, Gore stressed.

He exhorted the audience of geophysicists, atmospheric scientists and other researchers to take up the fight with renewed vigor. Gore told them to persevere despite the entrenched resistance he and other advocates have faced in their quest to shift the world economy away from polluting fossil fuels and toward cleaner sources of renewable energy.

"Every great moral cause that we have faced as a civilization has met with numerous 'no's," Gore said, citing women's suffrage, the abolition of slavery, the end of apartheid in South Africa, and the civil rights and gay rights movements, among other examples.

"All of those struggles met with ferocious resistance and one 'no' after another, but when it was eventually resolved into a binary choice between what is right and what is wrong, the outcome became inevitable because of who we are, 99 percent of us," he added. "And the struggle to save the climate balance, and to solve the climate crisis, is now yielding to that binary choice. But we are in a race against time. Damage is being done every single day."

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

The consequences of global sea level rise could be even scarier than the worst-case scenarios predicted by the dominant climate models, which don't fully account for the fast breakup of ice sheets and glaciers, NASA scientists said today (Aug. 26) at a press briefing.

What's more, sea level rise is already occurring. The open question, NASA scientists say, is just how quickly the seas will rise in the future.

Rising seas

The current warming of the seas and the associated expansion of their waters account for about one-third of sea level rise around the world. [Images of Melt: Earth's Vanishing Ice]

"When heat goes under the ocean, it expands just like mercury in a thermometer," Steve Nerem, lead scientist for NASA's Sea Level Change Team at the University of Colorado in Boulder, said in the press briefing.

The remaining two-thirds of sea level rise is occurring as a result of melting from ice sheets in Greenland and Antarctica and mountain glaciers, Nerem said.

Data collected by a cadre of NASA satellites — which change position in relation to one other as water and ice on the planet realign and affect gravity's tug — reveal that the ocean's mass is increasing. This increase translates to a global sea level rise of about 1.9 millimeters (0.07 inches) per year, Nerem said.

Unpredictable pace

But the speed of sea level rise is an open question.

"Ice sheets are contributing to sea level rise sooner, and more than anticipated," said Eric Rignot, a glaciologist at the University of California, Irvine, and NASA's Jet Propulsion Laboratory in Pasadena, California.

That's because people have never seen the collapse of a huge ice sheet and therefore don't have good models of the effects, Rignot said.

The Intergovernmental Panel on Climate Change, an international organization created by the United Nations that produces climate change models, has predicted that sea levels could rise as much as 21 feet (6.4 meters) in the next century if global warming continues unabated.

But even that worst-case scenario may not capture the risk, Rignot said. That's because the IPCC models only take into account temperature changes at the surface of glaciers, but not the rapid melting that occurs when glaciers calve and break up into the ocean, Rignot said.

In addition, much of glaciers' melting occurs at deep, undersea ice canyons. Warmer water is salter and therefore heavier. That means it sinks into the deeper layers of the ocean, and the contrast between this warm water and the undersea ice canyons contributes an unknown but substantial amount of sea level rise, said Josh Willis, an oceanographer at JPL in Pasadena, California.

When the massive Jakobshavn glacier in Greenland calved earlier this summer, it moved 4.6 square miles (12 square kilometers) of ice in one day, Rignot said. [See Photos of Greenland's Melting Glaciers]

If the Jakobshavn glacier had melted completely, "it contains enough ice to raise global sea level by half a meter — just this one glacier in Greenland," Rignot said. If all the land ice on the planet were to melt, it would raise sea levels about 197 feet (60 m), he added.

Some of the melting that has already occurred is likely irreversible, and could take hundreds of years to reverse, Rignot said.

American impact

While global sea levels have risen about 2.75 inches (7 centimeters) over the past 22 years, the west coast of the United States has not seen much of a rise in ocean levels. That's largely because of a long-time-scale weather pattern called the Pacific Decadal Oscillation, which is masking the global effect. That, however, could reverse in the coming years, Willis said.

"In the long run, we expect the sea levels on the west coast to catch up to global mean and even exceed the global mean," Willis said.

Florida is also particularly vulnerable to sea level rise because its porous soil allows more seawater intrusion than does the soil in other coastal areas, Willis said.

Follow Tia Ghose on Twitterand Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

To illustrate global warming's possible effects on local weather, 13 nations from around the world created future weather reports in the lead-up to the UN Climate Summit yesterday (Sept. 23) in New York City.

In each weather report, meteorologists from countries including the United States, Brazil, Germany and Zambia put together short video forecasts for a day in 2050, predicting how a warming planet may lead to droughts, heavy storms and landslides the world over.

Though scientists are still not able to link global warming to any single weather event, models and other research have shown that as the world warms, different regions can expect more extreme weather, increased volcanic activity, ocean acidification and even rising pollen counts. Climate change is the "single biggest risk to the global economy today," said leaders at the 2014 Clinton Global Initiative in New York City this week. [8 Ways Global Warming Is Already Changing the World]

What's more, researchers are 95 percent sure that humans are causing global warming, which has been observed since the 1950s, according to a 2013 report from the Intergovernmental Panel on Climate Change (IPCC).

If the world's greenhouse-gas emissions continue to rise at the current rate, the average temperature of Earth's lower atmosphere could increase more than 7.2 degrees Fahrenheit (4 degrees Celsius) by the end of the 21st century, the United Nation's World Meteorological Organization (WMO) said in a statement.

How might warmer temperatures heat up daily life? The meteorologists, from Japan to Iceland, gave their best predictions based on data from the latest Intergovernmental Panel on Climate Change (IPCC) report.

Brazil submitted the first weather prediction. In June 2050, people may see heavy rainfall in southern Brazil and the west Amazon.

"In a few days, the rain will exceed the amount expected for the entire month, which increases the risk of flooding and landslides,” Brazilian presenter Claudia Celli said in the video. Northern Brazil and the East Amazon, in contrast, are trudging through another day of drought "with no possibility of rain," Celli said.

Researchers have already found possible links between climate change and extreme weather this year in Brazil, Celli said. "In late autumn, heavy storms reached southern Brazil. In Paraná state, 150 cities were in a state of emergency, three of them were declared public calamities," she said. "In three days, the amount of precipitation was three times above the historical average. Eleven people died, houses and bridges were swept away by the water and many people lost all they had. The cost was millions of dollars." [In Images: Extreme Weather Around the World]

The WMO released one video every day from Sept. 3 to Sept. 22. In Japan, Hiroko Ida predicted a heat wave and 6,500 weather-related deaths in 2050.

The United States foresaw hurricanes pummeling the East Coast, a heat wave disrupting Chicago and a megadrought lingering in the Southwest. Iceland expected warm temperatures and increased rain in lieu of snow. The weather shift may help forests grow, but the warm weather may also bring insects that attack native plants in the future.

Warmer ocean temperatures around Iceland may lead some fish to move northward, and increased ocean acidity may also decrease fishery populations, the presenter reported.

Other countries that participated include Denmark, Burkina Faso, Bulgaria, South Africa and Tanzania.

"Climate change is affecting the weather everywhere. It makes it more extreme and disturbs established patterns. That means more disasters, more uncertainty," Ban Ki-moon, U.N. Secretary-General, said at the end of each video.

"We can reduce the risks by cutting global greenhouse gas emissions and building low-carbon economies," Ki-moon added. "Let's work together to make our societies safer and more resilient. Please join me in taking action on climate change."

Follow Laura Geggel on Twitter @LauraGeggel and Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

Climate change has already taken a serious toll on human well-being and world economies, and the world is generally poorly prepared to deal with the immediate and future threats imposed by a warming planet.

These are the results of the most recent report from the United Nation's Intergovernmental Panel on Climate Change (IPCC), a group that has been developing reports on climate change since 1988.

More than 700 scientific authors and editors contributed to the report that was released yesterday (March 30), titled "Climate Change 2014: Impacts, Adaptation, and Vulnerability," and many of those contributors convened in Yokohama, Japan, last week to share their findings with representatives of about 100 governments. The group held hearings in which they articulated just how bad the current situation is and what options and limits governments currently face in considering ways of adapting to changes in heat waves, flooding and other climate hazards in the future. [8 Ways Global Warming Is Already Changing the World]

"We do not only focus on heat waves, flooding, sea level rise, and other global and distant trends, but on their immediate effects on infrastructures, human health, water resources and other things we humans value," Patricia Romero-Lankao, a researcher at the National Center for Atmospheric Research in Boulder, Colo. and an author on the report, told Live Science while she was in Yokohama.

The group deliberately emphasized climate change's broad effects on humans living today, not in the distant future.

"One of the most important findings is that we are not in an era where climate change is some kind of future hypothetical," Chris Field, a researcher at the Carnegie Institution for Science and co-chair of the IPCC group responsible for producing this report, said during a news conference Sunday (March 30). "We see impacts from the equators to the poles, and from the coasts to the mountains. There is no question that we live in a world that is already altered by climate change."

Michael Mann, a climate scientist at Pennsylvania State University who was not an author but was an independent expert reviewer of this latest report, thinks the report does a better job than previous ones in making clear the immediacy of climate change.

"The report goes into far greater detail than past reports in outlining how climate-related stresses on water, land and food are already leading to increased conflict, and how climate change will increasingly become a national security threat as warming continues," Mann told Live Science.

Every continent on Earth has already experienced some effect of climate change, Mann said. Different regions face different kinds of threats, from rising sea levels around low-lying Pacific islands, to increased drought and heat waves elsewhere in the world.

An additional report from the IPCC will be released April 11, and will cover options for mitigating climate change.

Follow Laura Poppick on Twitter. Follow us @livescience, Facebook & Google+. Original article on Live Science.

NEW YORK — Famed climate scientist and activist James Hansen has said it before, and he'll say it again: Two degrees of warming is too much.

International climate negotiators agreed in the Copenhagen Accord, a global agreement on climate change that took place at the 2009 United Nations' Climate Change Conference, that warming this century shouldn't increase by more than 2 degrees Celsius (3.6 degrees Fahrenheit) to avoid the worst impacts of climate change. But in a new paper published in the open-access journal PLOS ONE, Hansen and a cadre of co-authors from a wide array of disciplines argue that even 2 degrees is too much, and would "subject young people, future generations and nature to irreparable harm," Hansen wrote in an accompanying essay distributed to reporters.

The new study is a departure from the typical climate science paper, both for the wide variety of fields represented in the list of co-authors, which includes economist Jeffrey Sachs, as well as for the policy implications it raises, something climate scientists tend to shy away from. The authors also plainly state that humanity has a moral obligation to future generations, the type of statement scientists also tend to avoid.

Hansen and Sachs met with reporters here Tuesday (Dec. 3) in Columbia University's Low Library to discuss their study and their thoughts on the ongoing — and so far, largely ineffectual — effort to come up with a global plan to combat the problem of climate change and scale back emissions of greenhouse gases, primarily carbon dioxide.

"It seems like we're just charging ahead, burning any and every fossil fuel," Hansen told reporters. "There seems to be no real effort to get off that business-as-usual path."

Hansen, noted for his outspokenness on the topic of climate change and his willingness to venture into an advocacy role that many other climate scientists try to avoid, has previously voiced his concern about the 2-degree warming benchmark, saying in 2011 at the annual meeting of the American Geophysical Union (AGU) that, "the target that has been talked about in international negotiations for 2 degrees of warming is actually a prescription for long-term disaster."

At the time, Hansen was still the director of NASA's Goddard Institute for Space Studies in New York. He retired from that position in April, in part, to pursue political and legal efforts on combating climate change. (Hansen had already used vacation time to attend climate protests and was arrested or cited several times, including in front of the White House.)

Hansen began the new study three years ago as a way "to provide a basis for legal actions for governments for not doing their jobs for protecting the rights of young people and future generations" after a conversation he had with a legal scholar. Hansen plans to discuss these legal actions in more detail at the 2013 meeting of the AGU, taking place next week in San Francisco.

'We can't accept that'

Hansen and his co-authors say Earth's climate history suggests the level of emissions cited to stay below the 2-degree threshold would result in "a significantly different planet" than the one humans know today and the one seen during the past 10,000 years of geologic history, called the Holocene, during which human civilizations evolved and flourished. The authors note that many impacts of climate change are already visible, from the shrinking ranges of some species to the frequency of extreme heat waves. [8 Ways Global Warming is Already Changing the World]

The study also reveals conditions during another period called the Eemian, about 120,000 years ago, when temperatures are thought to have been about 2 degrees Celsius higher than they were from 1880 to 1920 (the period the researchers used for preindustrial measurements). Some studies have suggested that sea levels during that time were several meters higher than they are today; such an increase in sea levels would threaten, and could even inundate, coastal cities.

"We can't accept that," Hansen said. "If we have any love for our children and grandchildren, we can't accept that."

The aim in limiting greenhouse gas emissions should be to keep Earth's climate as close as possible to what it has been during the Holocene, say the study authors, adding that doing so depends on the cumulative amount of emissions released into the atmosphere throughout the industrial period, not just those emitted today.

So far, some 370 gigatons of carbon (GtC) have been emitted into the atmosphere over the span of the industrial era. Since then, the levels of emissions have continued to rise, as countries like China begin to overtake Western countries, which are responsible for the majority of the emissions released to date. Most of today's emissions come from the burning of coal.

To have a 50 percent shot at not surpassing the 2-degree warming limit, the fifth assessment of the Intergovernmental Panel on Climate Change noted that emissions should not exceed about 1,000 GtC by 2100. But Hansen and his co-authors argue this emissions' limit must be cut in half to draw carbon dioxide levels down to 350 parts per million from their current level of 395 ppm (the highest they have been in 3 million years) and to stabilize global temperatures. That's because of feedbacks in the climate system, such as Arctic ice melt and changes to cloud cover, as well as the potential melting of ice sheets. Taking such feedbacks into account, 1,000 GtC would likely result in a temperature rise of at least 3 degrees Celsius, the authors say, and the impacts from climate change would be "locked in" (impossible to reverse) for the future after 2100.

Part of problem is that even with current levels of emissions, the inertia of the climate system means that not all of the warming those emissions will cause has happened yet — a certain amount is "in the pipeline" and will only rear its head in the future, because the ocean absorbs some of the heat, delaying the inherent atmospheric warming for decades to centuries.

"This paper makes extremely clear what the costs of the current trajectory are," Sachs said.

The oceans also absorb some of the carbon dioxide emitted into the atmosphere, which affects efforts to reduce carbon dioxide levels in the atmosphere — as less carbon dioxide is emitted into the atmosphere, the oceans will release some carbon dioxide so that the two systems stay in balance.

Hansen and his co-authors say this emphasizes the urgency of starting to reduce emissions now; the longer the delay in starting, the longer it will take to reduce levels to 350 ppm. The paper gives this example: If emissions stopped in 2015, 350 ppm would be reached by 2100; but if they weren't stopped until 20 years from now, levels wouldn't settle to 350 ppm until 2300.

Of course, completely ending emissions is unrealistic, but the paper's authors argue that 350 ppm could still be reached by 2100 if emissions' reductions are started soon and if some amount of carbon is drawn down into the biosphere and soil through efforts like reforestation and more efficient agriculture.

The team calculates that if emissions' reductions began today, they would need to occur at the rate of 6 percent per year (whereas if they had started in 2005, they would only have needed to be 3.5 percent per year) to keep the global temperature within about 1-1.5 degrees Celsius of preindustrial levels.

"We conclude that it is urgent that large, long-term emission reductions begin soon. Even if a 6 percent/year reduction rate and 500 GtC are not achieved, it makes a huge difference when reductions begin," the authors wrote. "There is no practical justification for why emissions necessarily must even approach 1,000 GtC." [To Cut Carbon, A Decade Is Too Long to Wait (Op-Ed)]

Even with immediate, aggressive reductions, Hansen said it was likely that by the end of the century, temperatures would pass the 1-degree mark, but that they don't have to pass 2 degrees. He added that the 1-degree goal could be achieved in the long-term.

Of course, to "to de-carbonize the energy system deeply" would require a level of global cooperation not seen so far, Sachs said, as well as a new way of approaching climate negotiations, something he is working on with nations ahead of climate meetings in 2014 and 2015. "Our current approach is not working, and we need to do something very, very different," because if humanity waits, the "dangers are profound," Sachs said.

Sachs, Hansen and their co-authors advocate a carbon tax to limit emissions. Not only would such a carbon tax be relatively easy to scale to a global system, but it would also take the health and environmental effects of fossil fuels into account, putting clean energy — from wind to nuclear — on an equal footing.

"The solution has got to involve making fossil fuels pay their cost to society," Hansen said.

'Value-laden work'

The authors "make a compelling case, based on an exhaustive review of the science, economics and arguments about intergenerational ethics, that dangerous climate change should be defined by a threshold of 350 ppm (below current levels) and just 1C total warming relative to preindustrial time (we have nearly reached that already), rather than the typically cited 2C warming/450 ppm limit," Penn State climate scientist Michael Mann, who wasn't involved in the study, told LiveScience in an email. Mann said that he saw the paper as "less a scientific article than an extended commentary," but one that he thought was beneficial to the scientific discourse.

Stanford climate scientist Ken Caldeira was more apprehensive about the nature of the study. Whereas the information in the study was important and "a welcome addition to the scientific literature," he is "concerned about the presentation of such a prescriptive and value-laden work" in a piece that wasn't marked as an opinion, Caldeira told LiveScience in an email.

Caldeira also said the question of whether an emissions' reduction goal should be aimed at a 2-degree-warming threshold or a 350-ppm level of carbon dioxide was something "science alone cannot tell us" and that "our goals depend on our values." In the same vein, the choice of using a carbon tax over other possible tools to reduce emissions was a matter of judgment about political goals, he added.

Though they are aware of the difficulty and scale of the problem of beginning meaningful cuts to greenhouse gases, Hansen and Sachs remain optimistic that humanity can solve the problem. "This is a winnable proposition … but it's hard," Sachs said. "It's definitely the hardest public policy problem I've ever seen."

Follow Andrea Thompson @AndreaTOAP, Pinterest and Google+. Follow us @livescience, Facebook & Google+. Original article on LiveScience.

Countries tallying their total greenhouse gas emissions can now get a better estimate thanks to two new reports adopted this week by the Intergovernmental Panel on Climate Change at a meeting in Batumi, Georgia.

One report improves the total greenhouse gas inventory for countries participating in the Kyoto Protocol, the international treaty to limit greenhouse gas emissions. The other report is a more accurate assessment of gases emitted and absorbed by wetlands.

The reports will help countries improve their greenhouse gas emissions inventories, Jean-Pascal van Ypersele, vice chair of the IPCC, said today (Oct. 18) at a news conference announcing the final reports.

"To mitigate climate change means to know well where the emissions of greenhouse gases come from and also how natural systems absorb some of them," Van Ypersele said.

Under the Kyoto Protocol, developed countries report their greenhouse emissions and removals (such as carbon trapped by trees). The IPCC's new methodology report updates the methods for estimating man-made greenhouse gas emissions, and removal by sinks resulting from land use activities, such as planting new forests.

The new wetlands report fills in a substantive knowledge gap, Thelma Krug, co-chair of the IPCC's Task Force on National Greenhouse Gas Inventories, said during the news conference.

"Wetlands draining and rewetting is a new elective activity [for reporting] under the Kyoto Protocol," Krug said. "The IPCC report provides guidance on how to meet those requirements in a more complete and more accurate way."

Both methodology reports went through the same multiyear review process as the IPCC's better-known climate change reports. Scientific experts analyzed the early drafts, and then government representatives provided comments, before both groups came together in Batumi to hash out the final report.

The IPCC released a summary of its fifth annual climate change report in September, the first major assessment since 2007. Among the new findings is the strongest certainty to date, 95 percent, that people are responsible for global warming. The report warns that cuts are needed in greenhouse gas emissions to keep an increase in average global temperature below 3.6 degrees Fahrenheit (2 degrees Celsius) by 2100.

Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on LiveScience.

Every corner of the world's oceans — from pole to pole and sea surface to seafloor — will undergo chemical changes associated with global climate change by 2100, jeopardizing the livelihoods of billions of people who subsist on marine ecosystems, according to a new study.

Previous studies addressing the effects of climate change on future ocean health have tended to focus on the effects of increased temperature and acidity on marine ecosystems. However, other oceanic conditions — including dissolved oxygen and productivity, or the abundance of tiny plant-like organisms that form the base of the marine food web — also play an important role in overall ocean health. As is the case on land, marine animals need oxygen and plant-life to survive. [Video: Humans Hit the Oceans Hard]

A team of 29 international scientists based at the University of Hawaii, Honolulu, have now developed more comprehensive projections of future ocean health, which take into account temperature, acidity, dissolved oxygen and productivity. To develop these projections, the researchers compiled more than 80,000 existing modeled maps of oceanic change, many of which informed the latest Intergovernmental Panel on Climate Change (IPCC) report.

The team found that mangrove and coral reef ecosystems near the tropics will likely experience the smallest cumulative change by 2100, whereas cetaceans (the group of mammals that includes whales, dolphins and porpoises), as well as pinnipeds (such as seals and walruses) will face the largest amount of change.

"We already knew that coral reefs are very susceptible to temperature change, and our models show that they are going to be impacted the least," study co-author Camilo Mora, a researcher at the University of Hawaii, Honolulu, told LiveScience. "So you can imagine what it's going to be like for other ecosystems."

The team used the compiled maps to estimate the impact these changes will have on coastal human populations whose livelihoods depend on marine resources.

Researchers considered two different climate change scenarios: one in which humans significantly cut back carbon dioxide emissions and, as a result, global atmospheric carbon dioxide levels increase from the current 440 parts per million (ppm) to just 550 ppm; and one in which humans continue emitting carbon dioxide at the current rate, under a scenario known as "business as usual," which the IPCC projects will result in an atmospheric carbon dioxide accumulation of 900 ppm by the end of the century. (Parts per million is an indicator of the concentration of a chemical in, for example, air. So in this case, 440 ppm means that there are 440 molecules of carbon dioxide in every million molecules of air.)

Under the 550-ppm scenario, the team estimated that 1.4 billion people would face considerable local oceanic change by 2100. Of those people, 690 million will live in countries with medium to high ocean dependence — a metric the researchers developed of the extent to which a society's jobs, revenue and food depend on the ocean.

Under a business-as-usual scenario, 2 billion people will face considerable oceanic change by 2100, with 1.12 billion of them living in countries with medium to high dependence on the ocean. Of those 2 billion people, 870 million will live in low-income countries with few resources to adapt to the projected changes.

The team notes that these estimates are rough, and that the specific ways in which ecosystems and communities adjust to change will remain largely unknown until the changes unfold.  

Mora likens this uncertainty to the uncertainty of falling off of a ladder: Some sort of injury is inevitable, but the exact body part or degree of injury remains unpredictable until a person hits the ground.

"Systems are very complex," Mora said. "You can't tell what species are going to go extinct, or the response of a specific species, but you can expect these changes to be quite massive."

The researchers hope to continue synthesizing new data as it becomes available, in order to continue honing the precision of their predictions.

The new findings are detailed today (Oct. 15) in the journal PLOS Biology. 

Follow Laura Poppick on Twitter. Follow LiveScience on Twitter, Facebook and Google+. Original article on LiveScience.

Michael Brune is executive director of the Sierra Club. This Op-Ed was adapted from one Brune wrote for his blog Coming Clean. He contributed this article to LiveScience's Expert Voices: Op-Ed & Insights.

The Intergovernmental Panel on Climate Change was set up in 1988 by two United Nations agencies as a way to collect and disseminate the current best science on climate disruption.

Since then it has issued four assessment reports. Recently, the IPCC began releasing its fifth assessment (known as the AR5). The first part is a "Summary for Policymakers." You can find it here, but there are five things you really need to know about it.

First, the scientific work reported by the IPCC in the AR5 is the gold standard for getting a big-picture understanding of what's happening to the climate. The report itself has 259 authors from 36 countries. They are scrupulous about quantifying the certainty of both findings and projections. This report is the best tool society has for making informed, rational decisions on how to deal with climate disruption.

Second, there is a lot of bad news: Several effects of climate disruption have accelerated during the past decade, such as the loss of Arctic sea ice, the melting of big glaciers and the rise of sea levels.

Third, not only are the adverse effects of climate disruption clearly evident today, they're also speeding up. In fact, 12 of the warmest years in recorded history occurred during the last 15 years — and the IPCC report says it's only going to get more intense.

Fourth, although global warming and climate disruption are the best-known consequences of carbon pollution, they're not the only ones people should worry about. The oceans absorb carbon from the atmosphere, and as they do, they become more acidic. This acidification is already killing coral reefs around the world. Ultimately, it could disrupt the entire marine food chain. Ours is a water planet. Do we really want to risk killing our oceans?

OK, enough with the scary stuff. The fifth thing you need to know is the single most important takeaway from the AR5: It's not too late. Society still has time to do something about climate disruption. The best estimate from the best science is that people can limit warming from human-caused carbon pollution to less than 3.6 degrees Fahrenheit (2 degrees Celsius) — if society acts now.

Bottom line: Our house is on fire. Rather than argue about how fast it's burning, the people of this planet need to start throwing buckets of water. We're going to need a lot of buckets. We'll also need to be smart about how we use them.

Our top priority must be to reduce our dependence on dirty fossil fuels like coal, oil, and gas, while boosting clean energy such as wind- and solar-power. The proposed carbon-pollution standards for new power plants that the Obama administration recently announced take aim at our single biggest source of carbon pollution: coal . If you care about climate disruption, the most important thing you can do right now is voice your support for these protections, and get ready for an even more important fight next year to clean up pollution at power plants already in operation.

But President Obama also has some other big tools at his disposal: Rejecting the Keystone XL pipeline, ending destructive oil and gas drilling in the Arctic and on public lands, stopping mountaintop-removal mining, curbing fossil fuel exports, and closing loopholes that exempt drilling and fracking for oil and gas from fundamental environmental protections.

You can bet that the Sierra Club and our millions of members and supporters will work hard to see that he uses those tools. Just as important, we'll also work to help develop the clean-energy solutions that will take the place of those dirty fuels. Every wind turbine, every solar panel, and every energy-efficient building is another step toward a clean-energy future.

The best climate scientists on the planet have sounded the alarm. Let's get to work.

This Op-Ed was adapted from "Five Things You Need to Know About the Big New Climate Report" whichappeared on Brune's blog Coming Clean. The views expressed are those of the author and do not necessarily reflect the views of the publisher. This version of the article was originally published on LiveScience.

The latest landmark climate change report from the Intergovernmental Panel on Climate Change was released today (Sept. 27), and it states the most certainty to date of humanity's role in causing global warming and climate change.

What makes this report stand out from the last four is that IPCC has presented climate mitigation scenarios. Want to hold global warming below 3.6 degrees Fahrenheit (2 degrees Celsius) and stop Greenland from melting? The IPCC report recommends a greenhouse gas emissions cutoff.

The IPCC report said that to keep global warming below 3.6 F, global carbon emissions would have to remain below 1,000 billion tons. This carbon "budget" accounts for the 500 billion tons that were released by 2011, so the lowest emissions scenarios have carbon output peak around 2020 and decline soon after.

"We have a choice," said Gerald Meehl, a report author and senior scientist at the National Center for Atmospheric Research in Boulder, Colo. "When you look at these different scenarios, for example, when you see a nearly ice-free Arctic in summer by mid-century, we can choose a different future. We can choose what future we have by the choices we make right now."

The report's science assessments also differ in significant ways from the last major appraisal, released in 2007. One highlight is that climate models now more closely reproduce natural climate patterns, increasing the certainty of future predictions of rising temperatures and changing weather patterns, said Lynne Talley, a report author and physical oceanographer at the Scripps Institution of Oceanography in San Diego. [Infographic: Global Warming Evidence: 2007 Report Compared to 2013]

Better insights into ice sheet melting, gained through polar research campaigns, have greatly improved sea level rise estimates, Talley said. Scientists also know more about how the ocean stores heat. While land-dwelling humans may focus on rising air temperatures, 93 percent of the added heat in the past century from global warming has come in the form of warmer ocean waters, the IPCC reported.

Faster sea level rise

The report is virtually certain (99 to 100 percent confidence) the ocean waters will continue their crawl into coastlines during this century.

By 2100, sea levels are likely to rise by between 10 and 32 inches (26 to 82 centimeters) from a combination of melting glaciers and ice sheets, and warming ocean water, which expands when heated. In 2007, the IPCC projected 7 to 23 inches (18 to 59 cm) of sea level rise for a similar greenhouse gas emissions scenario.

"I am really pleased that the sea level projections are more complete," said David Vaughan, a report author and climate scientist with the British Antarctic Survey. "We're really honing in on the amounts of sea level rise we're going to get."

But it is still unclear where exactly that water will go. "Not everybody is going to see sea level rise in the same way. Some will see more than others," Vaughan told LiveScience.

Changing rainfall

Climate models suggest rainfall patterns will change by 2100, with wet regions getting wetter and dry regions getting drier. There will be regional variations, of course, but some places could get up to 50 percent more precipitation, the new report said.

The shift is already taking place: Scientists have reported the ocean's surface waters are getting less salty in spots where rain is increasing, and more salty where the climate is drier. Rainfall changes were only lightly touched on in the  2007 report.

"We're seeing changes in the water cycles, and part of that evidence comes from the oceans," said Gregory Johnson, a report author and oceanographer at NOAA's Pacific Marine Laboratory Environmental Laboratory. [Video: Climate Change Impact: NASA's 21st Century Predictions]

Acidic oceans

Thirty percent of the excess carbon dioxide added to the atmosphere ends up in the ocean, where it forms carbonic acid. The increased acidity in ocean water is eating away at coral reefs and making it harder for oysters to build shells.

"The pH has decreased by about 0.1 by about since the beginning of the Industrial Age," Johnson told LiveScience. "This corresponds to a 26 percent increase in acidity. We don't assess the impacts, just the changes, but I think it will be an important part and something people are going to talk about," Johnson said.

Global temperatures rising

The report predicts that Earth's surface temperatures will likely rise (66 percent confidence) by 2.7 to 8.1 F (1.5 to 4.5 C) if carbon dioxide concentrations in the atmosphere double. Though the lower end of this range falls below the riseestimated in the 2007 report (3.6 F, or 2.0 C), the new range is the same as in IPCC reports issued before 2007.

Separately, the report projects that global average temperatures will rise between 0.5 to 8.6 F (0.3 to 4.8 C) this century, depending on different carbon emission scenarios.

The IPCC report has also shifted from talking about carbon emissions in parts-per-million, which counts one molecule of carbon dioxide in one million molecules of air, to the more easy-to-understand tons. [Infographic: Climate Change Evidence: 'Unprecedented' Warming Is Man-Made]

Explaining the pause

In the past 15 years, surface temperatures have increased more slowly than in the 1970s and 1980s. (However, the upper ocean continues to warm by 0.2  F (0.1 C) every decade, and the speed at which the ice sheets are melting shot up in the past 10 years).

The IPCC concludes that the short-term trend is caused by natural climate variability, with some of the heat that would go into surface warming instead being stored in the deep ocean instead, and by short-term cooling caused by volcanic eruptions, along with a solar minimum that decreased the amount of the sun's radiation hitting Earth.

"Even though we have this global pause, sea level is continuing to rise," said Graeme Stephens, a report author and climate scientist at the Jet Propulsion Laboratory in Pasadena, Calif. "So we think the heat is going into deep oceans, but we're not 100 percent sure."

More certainty

This time around, the IPCC report is 5 percent more confident (95 percent) that humans have “been the dominant cause of the observed warming since the mid-20th century.” That's an increase from 90 percent certainty in 2007.

"Warming is unequivocal," Dennis Hartmann, a report author and climate scientist at the University of Washington, said during a news conference following the report's release.

Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on LiveScience.com.

Scientists and other experts all over the world are reacting today (Sept. 27) to the report released by the Intergovernmental Panel on Climate Change (IPCC) stating that scientists are more certain than ever of the link between human activities and global warming.

In the report, climate scientists now say they are at least 95 percent certain that people are responsible for majority of the climate change effects seen since the 1950s, including warming oceans, melting ice and rising sea levels.

Thomas Stocker, co-chair of the report, called climate change "the greatest challenge of our time," and warned that without decisive action to reduce greenhouse gas emissions, many of the impacts of global warming will not only continue, but accelerate.

Today's report is the first of four that will make up the IPCC's Fifth Assessment Report. The remaining parts, which will examine the socioeconomic impacts of climate change and ways to mitigate its effects, will be released in 2014. [See how the 2013 IPCC report compares to previous predictions]

LiveScience reached out and asked scientists and other experts about their reactions to the report (published statements were also used). Here's what they said:

David Vaughan, IPCC author and climate scientist at the British Antarctic Survey

"Somebody said, what's the point? Actually I think it's a very good opportunity for the public, politicians and policymakers to reflect on climate change, and to just take a little while, while it's in the news, to absorb the new science and to reflect on what we might do about it.

"There's no right or wrong answer, and some countries may be more enthusiastic to cut carbon emissions, others to develop renewable energy, and developing countries may feel they must develop as fast as possible, but all of those strategies have impacts.

"The IPCC reports are really good times for society to reflect on the issues. We scientists are trying to bring everything up into public awareness in a way that it can be understood, and just put it on the map again. I think climate change, as an issue, has somewhat gone off the back burner. We've had a lot of international issues to deal with; maybe it's time to go back and reflect on what more we know. [Video - Climate Change Impact: NASA's 21st Century Predictions]

"I am really pleased that the sea level projections are made complete, that they have an Antarctica and Greenland dynamic contribution. We're really honing in on the amounts of sea level rise we're going to get.

"The thing we really need to do next is hone in on where that water will go — honing in on regional patterns of sea level rise. Really, not everybody is going to see sea level rise in the same way."

Camilla Toulmin, director of the International Institute for Environment and Development 

"The latest IPCC report confirms much of what we know already — that human activities are responsible for rising temperatures and increased climate instability across the world. Continued greenhouse gas emissions will unleash a wild mix of dangerous impacts.

"But there is also value in what the IPCC report does not say, such as how the climate will change from place to place. Climate models are not yet robust enough to predict impacts at local and regional scales, but it is clear from the experience of the many people with whom we work, who have faced loss and damage this year alone, that everybody is vulnerable in some way.

"This uncertainty about local impacts, coupled with the certainty that impacts will come, is a stark warning that everyone needs to get ready. Citizens and business leaders worldwide need to press governments to act, both at home and on the international stage."

Al Gore, environmentalist and former vice president of the United States (Gore shared a Nobel Peace Prize with the IPCC in 2007)

"The latest report by the IPCC is an important milestone in the study of climate science."

Gregory Johnson, IPCC author and oceanographer at the National Oceanic and Atmospheric Administration (NOAA)

"What this report has done is a careful analysis of all the signals we're observing in [the] changing climate — melting sea ice in the Arctic, melting glaciers, changes in the water cycles, changes in extreme events — and basically looked at the fingerprints of all those events and managed to attribute all those phenomena to a greater or lesser extent to climate change.

"The important thing to take away from this is there are multiple lines of evidence now that make us confident to the level of extremely likely that climate is changing." [8 Ways Global Warming is Already Changing the World]

Gerald Meehl, IPCC lead author and senior scientist at the National Center for Atmospheric Research

"The main message is the planet's warming. We're more certain now that humans are responsible — we're the dominant factor to affecting climate — we have this certainty. The certainty is extremely likely, which translates into 95 percent sure that's the case, we have better estimate of sea level rise, we now have ways to account to contributions for melting of Greenland and melting of west Antarctic ice sheets. [Image Gallery: Greenland's Melting Glaciers]

"There's much stronger evidence connecting human activity to changes in temperature, melting glaciers and ocean warming. There's a lot more evidence that connects human activity to changes in the climate system.

"I think when you look at the future projections and you look at these different scenarios, and you see the very high scenario when you don't do anything — as an example, we would have a nearly ice-free Arctic in [the] summer by near midcentury — you get those kind of fairly dramatic changes.

"But, we can choose a different future. We have a choice right now. We can choose what kind of future we have by the choices we make right now."

Michael Oppenheimer, professor of geosciences and international affairs at Princeton University and contributor to previous IPCC reports

"The important messages are that Earth has warmed significantly, most of the warming has to do with humans, Earth is going to keep warming under almost all future scenarios, and the chances of avoiding the 2-degree danger limits that governments have chosen is small, unless we get out there and develop and implement focused plans to start reducing emissions immediately.

"IPCC reports have been influential in getting governments' attention, even though they lag way behind where they should be. I expect this report to remind governments that they had better find a way to act together and act soon, although it's also true that a lot of governments are going at it on their own. Still, it would be better if they were more coordinated."

Saleemul Huq, senior fellow in the International Institute for Environment and Development's climate change group, and coordinating lead author of the IPCC's Working Group II report

"The IPCC has confirmed what many millions of people in the developing world are already well aware of, namely that the weather patterns have already changed for the worse. People in richer countries are vulnerable too, as recent floods, droughts and storms in Europe, North America and Australia have shown, but because of political inertia and powerful vested interests that have dominated media narratives for decades, they are less aware of the links between these impacts and their carbon emissions.

"Climate change affects us all and we must tackle it together. The time has come for global solidarity. This would enable the individual polluter (be they in a rich country or poor country) to recognize his or her personal responsibility and to try to connect with the victims of their pollution.

"Climate change ignores borders, but so do friendship and solidarity. It is time for national interests to give way to the global good. I hope the strong message from IPCC will galvanize actions by politicians and publics around the world."

LiveScience Staff Writer Becky Oskin contributed reporting.

Follow Denise Chow on Twitter @denisechow. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.

Observed changes in climate and greenhouse gases could be accounted for by human activity, according to a report by the Intergovernmental Panel on Climate Change (IPCC). Observations of the climate system are based on direct measurements and remote sensing from satellites and other platforms.

IPCC's 2007 report compared with 2013's:

TEMPERATURE

2007: 1995-2006 rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850).

2013: Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. 

SEA LEVEL

2007: Global average sea level has risen since 1961 at an average rate of 1.8 millimeters/yr and since 1993 at 3.1mm/yr.

2013: The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia.

SNOW AND ICE

2007: Observed decreases in snow and ice extent are also consistent with warming.

2013: Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass and glaciers have continued to shrink almost worldwide.

NORTHERN HEMISPHERE

2007: Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years.

2013: In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1,400 years (medium confidence). Northern Hemisphere spring snow covers have continued to decrease.

OCEANS

2007: Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.

2013: The global ocean will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation.

ECOSYSTEMS

2007: In terrestrial ecosystems, earlier timing of spring events and poleward and upward shifts in plant and animal ranges are with very high confidence linked to recent warming.

2013: Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. 

The report of the Intergovernmental Panel on Climate Change (IPCC), released in September 2013, called the evidence for warming of the Earth’s climate system “unequivocal,” and many of the changes observed since 1950 are “unprecedented” over decades to millennia. The scientists rated the findings of previous research according to confidence (from very low to very high) and probability (from exceptionally unlikely to virtually certain). The report said “with 95 percent certainty” that at least half of the observed changes could be accounted for by human activity. 

The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.

In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1,400 years. Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.

There are likely more land regions where the number of heavy precipitation events has increased than where it has decreased.

The frequency or intensity of heavy precipitation has likely increased in North America and Europe.

Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent.

Ocean warming accounts for more than 90 percent of the energy accumulated in the climate system between 1971 and 2010. It is virtually certain that the upper ocean to a depth of 2,300 feet (700 meters) warmed from 1971 to 2010.

The atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years.

CO2 concentrations have increased by 40 percent since pre-industrial times, primarily from fossil fuel emissions..

This story was updated at 9:05 a.m. EDT.

The Intergovernmental Panel on Climate Change's latest report on the science of global warming squarely blames humans as the primary cause of climate change, saying it is "extremely likely" that human activities have caused most of the warming of the planet's surface that has occurred since the 1950s.

The assessment, released today (Sept. 27), is the first major report from the Intergovernmental Panel on Climate Change (IPCC) since 2007, and presents the strongest case yet for human-caused global warming since the IPCC was established in the late 1980s.

"There's much stronger evidence connecting human activity to changes in temperature, melting glaciers and ocean warming," said Gerald Meehl, a senior scientist at the National Center for Atmospheric Research and one of the authors of the new report. "There's a lot more evidence that connects human activity to changes in the climate system."

In the new summary, climate scientists say they are at least 95 percent certain that people are responsible for the warming oceans, rapidly melting ice and rising sea levels that have been observed since the 1950s. The 2007 report linked human activities to climate change with 90 percent certainty, which was a considerable leap from the 66 percent probability stated in the organization's 2001 report. [8 Ways Global Warming is Already Changing the World]

"Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes," the new report says. "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century."

Dangerously high emissions

The scientists also warned that emissions of carbon dioxide and other greenhouse gases will need to be cut in order to keep the increase in average global temperature to less than 3.6 degrees Fahrenheit (2 degrees Celsius), and avoid the most devastating effects of global warming. The benchmark of 3.6 degrees Fahrenheit was set by climate negotiators in Copenhagen in 2009.

Given current patterns of emissions, approximately 1 trillion tons of carbon could be burned and emitted into the atmosphere before the increase in the planet's average surface temperature creeps above 3.6 degrees Fahrenheit, the panelists said. However, more than half of that amount has already been burned, Thomas Stocker, co-chair of the so-called Working Group I report, said at a news briefing this morning in Stockholm, Sweden.

"We cannot emit more than 1,000 billion [1 trillion] tons of carbon, of which already 54 percent has been emitted," Stockersaid. The report does not specify when and how emissions should be reduced, he said, "but we give very relevant guidance for the total amount of carbon that cannot be exceeded, in terms of emissions, in order to stay below 2 degrees Celsius [3.6 degrees Fahrenheit]."

Yet, some estimates indicate that even if measures are introduced today to reduce greenhouse gas emissions, the 3.6-degree limit will likely be surpassed by the end of the century.

The effects of climate change

The new assessment also contains updated projections for various climate scenarios, including sea level rise, melting glaciers and rising global average temperatures. [FAQ: IPCC's Upcoming Climate Change Report Explained]

If greenhouse gas emissions are not curbed, sea levels could rise as much as 3 feet (0.9 meters) by the year 2100, the scientists said. This is an increase from the estimated 0.9 to 2.7 feet (0.3 to 0.8 meters) of sea-level rise that was predicted in the 2007 IPCC report.

"The top estimate is about 3 feet, and that's quite a lot to deal with," Michael Oppenheimer, a professor of geosciences and international affairs at Princeton University in Princeton, N.J., and a contributor to previous IPCC reports, told LiveScience. "Sea level rise is a real problem because it poses very high risks around coasts."

Global temperatures are also likely to rise by between 0.5 and 8.6 degrees Fahrenheit (0.3 degrees and 4.8 degrees Celsius) this century, depending on global levels of carbon emissions.

"Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system," Stocker said. "Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions."

The report found that atmospheric concentrations of carbon dioxide, methane and nitrous oxide are now at levels that are "unprecedented" in at least the last 800,000 years.

Now what?

Panel members said they are hopeful the report will shape climate negotiations between nations, particularly in the lead up to the UN Conference on Climate Change scheduled to take place in Paris in 2015.

"Thanks to the dedicated work of [this] global community of scientists, we know the nature of the problem, and the options for addressing it," UN secretary general Ban Ki-Moon said in a video address to the audience in Sweden this morning. "The heat is on. Now we must act."

Today's assessment is part of the IPCC's latest summary on climate change, called the Fifth Assessment Report of AR5. The IPCC reports consist of four sections: the Working Group I report on the science of climate change; the Working Group II report on the vulnerabilities and socioeconomic impacts; the Working Group III report on possible ways to mitigate climate change; and the Synthesis Report, which reviews the findings from all the working groups and integrates relevant information for policymakers. The other sections of the IPCC's Fifth Assessment Report will be released in 2014.

The IPCC was established by the United Nations in 1988 to comb through the most recent published and peer-reviewed research on global warming, and put together comprehensive reports on the risks and impacts of climate change.

The assessments undergo an extensive review process that involves thousands of scientists and government officials, and the final products represent consensus within the scientific community. As a result, the IPCC reports are considered the authority on the risks and impacts of global warming.

LiveScience Staff Writer Becky Oskin contributed reporting.

Follow Denise Chow on Twitter @denisechow. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.

The Intergovernmental Panel on Climate Change (IPCC), an organization created by the United Nations to assess the state and science of global warming, will release part of its newest major report tomorrow (Sept. 27).

The report — known as the Fifth Assessment Report, or AR5 — will be the first assessment from the group since 2007. More than 250 scientists met in Sweden this week to finalize one section of the AR5: the Working Group I report. These findings, which examine the science of climate change, will be released tomorrow.

"This is the physical science basis for how and why the climate is changing, and how it might change in the future," said Alden Meyer, director of strategy and policy for the Union of Concerned Scientists, a science advocacy group headquartered in Cambridge, Mass. [Best of the IPCC Report Leaks]

The IPCC's latest assessment will likely raise the level of certainty that human activities are responsible for the last 50 years of global warming, said Heidi Cullen, vice president and chief climatologist for Climate Central, a nonprofit science journalism organization based in Princeton, N.J.

"Science is more certain than ever that the majority of the warming since 1950 has, indeed, been caused by human activity," she told reporters at a news conference earlier this month.

The IPCC report, which combs through all of the most recent published and peer-reviewed research on climate change, is also expected to provide updated information on sea level rise, melting ice, global average temperatures and extreme weather events, such as drought or heavy rainfall.

"Another place where I think we're going to see a big change in the IPCC report this time is how it deals with the role of ice loss in Greenland and Antarctica in sea level rise," said James McCarthy, a professor of biological oceanography at Harvard University in Cambridge, Mass., and an author, reviewer and co-chairman of previous IPCC reports.

"When we were wrapping up the Third Assessment [in 2001], it was not clear that one would expect to see large changes in the ice of Greenland over the next several decades," McCarthy told LiveScience. "What became clear to us — as we saw in 2002, 2003 and 2004 — [is that] we've been wrong. The Greenland ice is now changing faster in just a few years."

The IPCC reports reflect consensus within the scientific community on the state of global warming, and are designed to inform policymakers on the risks and potential impacts of climate change. The reports involve thousands of scientists from around the world who volunteer to write and review the report's four sections. The assessments are also reviewed by government officials from more than 120 participating countries.

The other sections of the AR5 — the Working Group II report that assesses the socioeconomic impacts of climate change, the Working Group III report that looks at mitigation factors, and the Synthesis Report that sums up all the findings and provides guidance for policymakers — will be released in 2014.

The IPCC will hold a news conference tomorrow at 10:00 a.m. CET (4:00 a.m. EDT) in Stockholm, where scientists have been meeting to discuss the Working Group I report. The news conference will be webcast live at ipcc.ch/webcast.

Follow Denise Chow on Twitter @denisechow. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

Michael Mann is Distinguished Professor of Meteorology at Penn State University and was recognized in 2007, with other IPCC authors, for contributing to the award of the 2007 Nobel Peace Prize for his work as a lead author on the "Observed Climate Variability and Change"chapter of the Intergovernmental Panel on Climate Change (IPCC) Third Scientific Assessment Report. Mann contributed this article to LiveScience's Expert Voices: Op-Ed & Insights.

It happens every six years or so: The Intergovernmental Panel on Climate Change (IPCC) publishes its assessment of the current state of scientific understanding regarding human-caused climate change. That assessment is based on contributions from thousands of experts around the world through an exhaustive review of the peer-reviewed scientific literature and a rigorous, several-years-long review process. Meanwhile, in the lead-up to publication, fossil-fuel industry front groups and their paid advocates gear up to attack and malign the report, and to mislead and confuse the public about its sobering message.

So in the weeks leading up to the release of the IPCC Fifth Assessment scientific report, professional climate-change deniers and their willing abettors and enablers have done their best to distort what the report actually says about the genuine scientific evidence and the reality of the climate-change threat. [FAQ: IPCC's Upcoming Climate Change Report Explained]

This time, however, climate-change deniers seem divided in their preferred contrarian narrative. Some would have us believe that the IPCC has downgraded the strength of the evidence and the degree of threat. Career fossil-fuel-industry apologist Bjorn Lomborg, in Rupert Murdoch's "The Australian," wrote on Sept. 16: "UN's mild climate change message will be lost in alarmist translation." On the other hand, serial climate disinformer Judith Curry, in a commentary for the same outlet five days later, announced, "Consensus distorts the climate picture."

So, make up your mind, critics: Is it a "mild message" or a "distorted picture?" Consistency, they might well respond, is simply the "hobgoblin of little minds" after all — but in reality, that's only if you ignore the foolishness.

Indeed, claims that members of the IPCC have downgraded their scientific confidence have been plentiful among the usual purveyors of climate-change misinformation: Fox News, the editorial pages of the Wall Street Journal and various conservative tabloids in the United States, Canada, Germany and Australia. Fox News even sought to mislead its viewers with a bait and switch, focusing attention instead on a deceptive, similarly named report that calls itself the Nongovernmental International Panel on Climate Change (NIPCC), which simply regurgitates standard shopworn denialist myths and erroneous talking points. That non-peer-reviewed report was published by the discredited industry front group known as the Heartland Institute in the lead-up to the publication of the actual IPCC report, presumably to divert attention from the actual scientific evidence.

In reality, the IPCC has strengthened the degree of certainty that fossil-fuel burning and other human activities are responsible for the warming of the globe seen over the past half century, raising their confidence from "very likely" in the previous report to "extremely likely" in the current one. The IPCC expresses similar levels of certainty that the Earth is experiencing the impacts of that warming in the form of melting ice, rising global sea levels and various forms of extreme weather. [Climate Scientists: IPCC Report Must Communicate Consensus]

What about the converse claim, promoted by critics, that the IPCC has exaggerated the evidence?

Well, if anything, the opposite appears closer to the truth. In many respects, the IPCC has been overly conservative in its assessment of the science. The new report, for example, slightly reduces the lower end of the estimated uncertainty range for a quantity know as the equilibrium climate sensitivity — the amount of warming scientists expect in response to a doubling of carbon dioxide (CO2) concentrations relative to preindustrial levels (concentrations that will be seen mid-century, given business-as-usual emissions).

The IPCC reports a likely range of 1.5 to 4.5 degrees Celsius (roughly 3 to 8 degrees Fahrenheit) for this quantity, the lower end having been dropped from 2.0 degrees C in the fourth IPCC assessment. The lowering is based on one narrow line of evidence: the slowing of surface warming during the past decade.

Yet there are numerous explanations of the slowing of warming (unaccounted for effects of volcanic eruptions and natural variability in the amount of heat buried in the ocean) that do not imply a lower sensitivity of the climate to greenhouse gases. Moreover, other lines of evidence contradict an equilibrium climate sensitivity lower than 2 degrees C. It is incompatible, for example, with paleoclimate evidence from the past ice age, or the conditions that prevailed during the time of the dinosaurs. (See this piece I co-authored earlier this year for the Australian Broadcasting Corp. for a more detailed discussion of the matter.)

The IPCC's treatment of global sea-level rise is similarly conservative — arguably, overly so. The report gives an upper limit of roughly 1 meter (3 feet) of sea-level rise by the end of the century under business-as-usual carbon emissions. However, there is credible peer-reviewed scientific work, based on so-called "semi-empirical" approaches that predict nearly twice that amount — i.e., nearly 6 feet (2 m) of global sea-level rise this century. These latter approaches are given short thrift in the new IPCC report; instead, the authors of the relevant chapter favor dynamical modeling approaches that have their own potential shortcomings (underestimating, for example, the potential contribution of ice-sheet melting to sea-level rise this century).

As some readers may know, the conclusion that modern warming is unique in a long-term context came to prominence with the temperature reconstruction that my co-authors and I published in the late 1990s. The resulting "Hockey Stick" curve, which demonstrates that the modern warming spike is without precedent for at least the past 1,000 years, took on iconic significance when it was prominently displayed in the "Summary for Policy Makers" of the 2001 Third IPCC Assessment report. Thus, the "Hockey Stick" curve, as I describe in my recent book, "The Hockey Stick and the Climate Wars," became a focal point of the attacks by industry-funded climate-change deniers.

So, it might not come as a surprise that one of the most egregious misrepresentations of the IPCC's latest report involves the Hockey Stick and conclusions about the uniqueness of modern warming. [4 Things to Know About the IPCC's Climate Change Report]

An urban legend seems to be circulating around the echo chamber of climate-change denial, including contrarian blogs and fringe right-wing news sites. The claim is that the IPCC has "dropped" or "trashed" the Hockey Stick conclusion regarding the unprecedented nature of recent warmth.

A good rule of thumb is that the more insistent climate-change deniers are about any particular talking point, the greater the likelihood is that the opposite of what they are claiming actually holds. The IPCC has, in fact, actually strengthened its conclusions regarding the exceptional nature of modern warmth in the new report. A highlighted box in the "Summary for Policy Makers" states the following (emphasis mine):

In the northern Hemisphere, the period 1983-2012 was likely the warmest 30-year period of the last 1400 years (medium confidence).

The original 1999 Hockey Stick study (and the 2001 Third IPCC Assessment report) concluded that recent Northern Hemisphere average warmth was likely unprecedented for only the past 1,000 years. The 2007 IPCC Fourth Assessment extended that conclusion back further, over the past 1,300 years (and it raised the confidence to "very likely" for the past 400 years). The new, Fifth IPCC Assessment has now extended the conclusion back over the past 1,400 years. By any honest reading, the IPCC has thus now substantially strengthened and extended the original 1999 Hockey Stick conclusions.

Only in the "up is down, black is white" bizarro world of climate-change denial could one pretend that the IPCC has failed to confirm the original Hockey Stick conclusions, let alone contradict them. [How Words Affect Climate Change Perception]

The stronger conclusions in the new IPCC report result from the fact that there is now a veritable hockey league of reconstructions that not only confirm, but extend, the original Hockey Stick conclusions. This recent RealClimate piece summarizes some of the relevant recent work in this area, including a study published by the international PAGES 2k team in the journal Nature Geoscience just months ago. This team of 78 regional experts from more than 60 institutions representing 24 countries, working with the most extensive paleoclimate data set yet, produced the most comprehensive Northern Hemisphere temperature reconstruction to date. One would be hard-pressed, however, to distinguish their new series from the decade-and-a-half-old Hockey Stick reconstruction of Mann, Bradley and Hughes.

Conclusions about unprecedented recent warmth apply to the average temperature over the Northern Hemisphere. Individual regions typically depart substantially from the average. Thus, while most regions were cooler than present during the medieval era, some were as warm, or potentially even warmer, than the late-20th-century average. These regional anomalies result from changes in atmospheric wind patterns associated with phenomena such as El Niño and the so-called North Atlantic Oscillation. [U.S. Will Warm Dramatically By 2084, NASA Model Shows (Video)]

Colleagues and I, quoting from the abstract of our own article in the journal Science a few years ago (emphasis mine), stated:

Global temperatures are known to have varied over the past 1,500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface-temperature patterns over this interval. The medieval period [A.D. 950-1250] is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally.

These conclusions from our own recent work are accurately represented by the associated discussion in the "Summary for Policy Makers" of the new IPCC report (emphasis mine):

Continental-scale surface-temperature reconstructions show, with high confidence, multidecadal periods during the Medieval Climate Anomaly (year 950-1250) that were, in some regions, as warm as in the late 20th century. These regional warm periods did not occur as coherently across regions as the warming in the late 20th century (high confidence).

However, never underestimate the inventiveness of climate-change deniers. Where there's a will, there is, indeed, a way: A meme now circulating throughout the denialosphere is that the IPCC's conclusions about regional warmth contradict our findings, despite the fact that those conclusions are substantially based on our findings.

One could be excused for wondering if climate-change deniers have lost all sense of irony.

The most egregious example of this latest contortion of logic found its way into the purportedly "mainstream" Daily Mail, courtesy of columnist David Rose, who admittedly has a bit of a reputation for misrepresenting climate scientists and climate science. Rose wrote in his column on Sep. 14, "As recently as October 2012, in an earlier draft of this report, the IPCC was adamant that the world is warmer than at any time for at least 1,300 years. Their new inclusion of the 'Medieval Warm Period' — long before the Industrial Revolution and its associated fossil-fuel burning — is a concession that its earlier statement is highly questionable."

The most charitable interpretation is that Rose simply didn't actually read or even skim the final draft of the report, despite writing about it at length. For, if he had, he would be aware that the final draft of the report comes to the strongest conclusion yet about the unprecedented nature of recent warmth, extending the original Hockey Stick conclusion farther back than ever before — to the last 1,400 years.

Moreover, he would be aware that the existence of regional medieval warmth rivaling that of the late 20th century does not contradict that conclusion — indeed, it is the regional heterogeneity of that warmth, as established in ours and other studies, that leads the IPCC report to conclude that current levels of hemispheric average warmth are unprecedented for at least 1,400 years.

The lesson here, perhaps, is that no misrepresentation or smear is too egregious for professional climate-change deniers. No doubt, we will continue to see misdirection, cherry-picking, half truths and outright falsehoods from them in the months ahead as the various IPCC working groups report their conclusions.

Don't be fooled by the smoke and mirrors and the Rube Goldberg contraptions. The true take-home message of the latest IPCC report is crystal clear: Climate change is real and caused by humans, and it continues unabated. We will see far more dangerous and potentially irreversible impacts in the decades ahead if we do not choose to reduce global carbon emissions. There has never been a greater urgency to act than there is now.

The latest IPCC report is simply an exclamation mark on that already-clear conclusion.

Mann is author of two books, "The Hockey Stick and the Climate Wars: Dispatches from the Front Lines" (Columbia University Press, 2012), which will soon to be available in paperback with an update and a new guest foreword by Bill Nye "The Science Guy", and "Dire Predictions: Understanding Global Warming" (DK Publishing, 2008). You can follow him on Twitter: @MichaelEMann. The viesws expressed are those of the author and do not necessarily reflect the views of the publisher. This version of the article was originally published on LiveScience.

This week, the Intergovernmental Panel on Climate Change (IPCC), an international organization established by the United Nations to assess the science, risks and impacts of global warming, will release its latest big report on the science of climate change — the group's first assessment since 2007.

The findings, which are based on the aggregated results of the most recent published and peer-reviewed climate change research, will be released Friday (Sept. 27), and represent the first of four sections that will make up the IPCC's Fifth Assessment Report, or AR5. Other parts of the report examine socioeconomic impacts and potential ways to mitigate the effects of climate change.

This week's so-called Working Group I report is expected to include summaries on melting glaciers, greenhouse gas emissions, sea level rise and the impact of human activities on the global climate. With its release only days away, here are four things to know about the IPCC report:

1. The report's estimates are conservative.

Thousands of scientists and other experts across a diverse range of fields participate in writing and reviewing the IPCC reports, which are generally released every five or six years. Drafts of the report are subject to an extensive review process, which includes hundreds of outside experts and representatives from more than 120 participating countries. [8 Ways Global Warming is Already Changing the World]

Since the IPCC reports are designed to represent consensus on the state of climate change within the scientific community, estimates on the consequences of global warming are typically conservative, with tendencies to underestimate rather than overestimate the potential effects.

"Scientists come to a consensus statement, which historically, has been very conservative," said James McCarthy, a professor of biological oceanography at Harvard University in Cambridge, Mass., who has been an author, reviewer and co-chair on previous IPCC reports. "It's a tedious process, but it's what gives this entire endeavor the value that it has."

2. While they attracts attention from the general public, the IPCC reports are really intended for policymakers.

As climate change issues have garnered more public attention across the globe, so too have the IPCC reports. But, while the research contained in the assessments may be of general interest, the reports are intended to help policymakers guide negotiations on climate policy.

When the IPCC was established by the U.N. in 1988, many of the contributing authors did not anticipate the amount of public interest seen in recent years.

"In the 1980s and 1990s, the IPCC was not really of any public interest — we were just doing a job, and the products were received by governments," said Richard Klein, a senior research fellow at the Stockholm Environment Institute in Sweden.

Since then, the level of interest in the IPCC reports has increased, as more parties feel they have a stake in the climate debate, said Klein, who is one of the authors of the AR5's Working Group II report, which is scheduled to be released in March 2014. [6 Unexpected Effects of Climate Change]

"Now there is a lot of public interest, corporate interest and interest among governments at all levels, including local governments," Klein told LiveScience. "I think it's fair to say there are very different expectations now with the IPCC, but at the same time, the objective is the same, and its primary audience remains governments.

3. The IPCC reports do not include original research.

The IPCC's mission is to collect and assess the most recent published and peer-reviewed research on climate change. From this extensive body of work, the teams of authors put together comprehensive assessments of the science of climate change, the potential impacts of global warming, and possible ways to mitigate the effects.

The report's authors do not conduct original research for the assessments, so the IPCC reports largely function as summaries of the state of the field.

4. The IPCC is considered the world's leading climate change advisory body.

As an intergovernmental organization that includes input from thousands of scientists and experts, the IPCC is considered the authority on climate change and global warming. The group's reports, with their focus on peer-reviewed research, undergo a meticulous review process involving thousands of scientists and government representatives.

"It's the most elaborate review and approval process for any scientific report in the world," said Alden Meyer, the director of strategy and policy for the Union of Concerned Scientists, a science advocacy group headquartered in Cambridge, Mass.

As a result, the findings of the IPCC reports, while conservative, are generally used as benchmarks in the field of climate research.

Follow Denise Chow on Twitter @denisechow. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.

With 800 volunteer reviewers, the latest report from the Intergovernmental Panel on Climate Change (IPCC) — the international body that assesses the state of the science on climate change — was bound to leak.

The first full version of the draft report was posted online in December 2012 by a climate change skeptic who was part of the volunteer review army. Now, as the report's Sept. 27 release date nears, final drafts are circulating among journalists.

This latest version of the IPCC's summary of climate sciencewill be called the Fifth Assessment Report, or AR5. Since the last report was issued in 2007, the IPCC has corralled experts from around the world to review, analyze and summarize existing research on global warming and climate change.

Here is a sneak preview of what to expect when the AR5 report is issued next week, based on the leaks so far. But be warned — there will be differences between the versions given to reporters and the IPCC's final statement. The last rewrite session begins Monday, Sept. 23, in Stockholm.

We did it

The biggest news is that the IPCC has raised their level of certainty that humans are responsible for the last 50 years of global warming, up to 95 percent from 90 percent in 2007. "There is high confidence that this has warmed the ocean, melted snow and ice, raised global mean sea level, and changed some climate extremes in the second half of the 20th century," the leaked drafts said. [NASA Video: Watch US Heat Up by 2100]

Antarctica is confusing

The Antarctic Ice Sheet shrank nearly five times faster between 2002 to 2011 than it did in the decade before, the report said. But Antarctic winter sea ice seems to cover a slightly bigger area each year. In the 2007 report, the IPCC models predicted a small decreasing trend in this winter Antarctic sea ice extent. Studies published this year attribute the increasing sea ice trend to changing wind patterns. The IPCC report may not have time to add these latest observations and models, and researchers are far from reaching consensus. The draft report said, "There is low confidence in the scientific understanding of the small observed increase in Antarctic sea ice extent."

It's hot out there

The report is unequivocal here: Global average temperatures will continue to rise. The IPCC projects warming will likely be above 2.4 degrees Fahrenheit (1.5 degrees Celsius) and very likely below 10.8 degrees Fahrenheit (6 degrees Celsius.) This is a rollback from 2007, when the likely low end of the warming range was pinned at 3.6 degrees Fahrenheit (2 degrees Celsius). For the IPCC, "likely" means 66 percent probability and "very likely" is 90 percent probability of occurring.

The IPCC also acknowledges a slowdown in warming in the past 15 years, which climate change skeptics say is evidence of a global cooling trend. There's no global cooling, according to the report. Temperatures continued to rise by 0.09 degrees Fahrenheit (0.05 degrees Celsius) per decade from 1998 to 2012. Between 1951 and 1998, the warming rate was 0.22 degrees Fahrenheit (0.12 degrees Celsius) per decade. (In 2007, the IPCC said the rate of warming was 0.13 degrees Celsius per decade.)

But even with this variability, the past 30 years were the warmest in several centuries, the report said. (A study published April 21, 2013, in the journal Nature Geoscience confirms this trend — the last three decades were the warmest in 1,400 years.)

The ice is melting

The pace of melting glaciers is rising, the report concludes. The Arctic ice pack is shrinking. As mentioned above, the massive Antarctic ice cap is also starting to show signs of responding to global warming by increasing its melting. The Greenland Ice Sheet lost about six times more ice from 2002 to 2011 than from 1992 to 2001 — an average of 177 billion tons a year versus 7 billion tons a year, respectively. [Video - Loss of Arctic Sea Ice]

Sea level rise is smaller, broader

The IPCC pared down its projections for global average sea level rise, partly because scientists have a better understanding of how glaciers will melt and the oceans will respond as the planet warms. Depending on future greenhouse gas emissions, sea levels will rise by an average of 16 to 24 inches (40 to 62 centimeters) by 2100, according to the leaked report. The full range of projected sea level rise, 11 to 32 inches (29 to 82 cm), is much broader than in 2007. The IPCC will explain the reasoning behind the new numbers next week.

Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on LiveScience.

The Intergovernmental Panel on Climate Change (IPCC), an international organization established to assess the science of climate change and the related environmental and socioeconomic impacts, will be releasing part of its latest report, the first in six years, this month.

The assessment, known as the Working Group I report, represents a summary of the most recent scientific research on climate change, including studies of sea level rise, melting glaciers and changes in global temperatures.

Next week, from Sept. 23 to Sept. 26, more than 250 climate scientists will meet in Stockholm, Sweden, to finalize the Working Group I report, which will be released on Sept. 27. Here are some frequently asked questions about the IPCC's assessments, and what we may expect to see next week.

What is the IPCC?

The Intergovernmental Panel on Climate Change was established by the United Nations Environmental Programme and the World Meteorological Organization in 1988.

The organization's mission is to collect and assess the most recent published work on climate change, and provide comprehensive assessments of the potential consequences. In addition to examining the environmental and socioeconomic impacts, the scientists also present ways to mitigate these effects. [8 Ways Global Warming is Already Changing the World]

The IPCC releases big, sweeping assessment reports on the state of climate change every five or six years. Previous IPCC reports were published in 1990, 1995, 2001 and 2007. The first section of the newest report, known as the Fifth Assessment Report, or AR5, will be released on Sept. 27, with three other parts expected to follow in 2014.

The IPCC is widely regarded as the leading international scientific advisory group on climate change and global warming, and the organization's reports reflect the agreement of the world's most prominent climate scientists. The IPCC's assessments are also used to inform policymakers on the risks of climate change, although significant governmental action has been slow.

Who is involved in the IPCC?

The IPCC is made up of thousands of scientists from universities and think tanks all around the world, who participate in writing and reviewing the four sections of the group's reports on a voluntary basis. The IPCC's assessments are also reviewed by the governments of more than 120 participating countries.

The IPCC has been chaired by Rajendra Pachauri since 2002.The organization does not conduct its own research, but rather integrates the findings of published studies within the scientific literature on climate change. The forthcoming IPCC report includes research published as recently as spring 2013.

What does the IPCC do?

The IPCC puts together a seminal report every five to six years, which is broken up into four main sections: the Working Group I report on the science of climate change; the Working Group II report on climate change impacts, adaptations and vulnerabilities; the Working Group III report on possible ways to mitigate climate change; and the final AR5 Synthesis Report, which combines the main findings from all the working groups and integrates relevant information to benefit policymakers. [6 Unexpected Effects of Climate Change]

Since the IPCC's conclusions require consensus among the panel members, the organization's reports tend to feature fairly conservative estimates, with a tendency to underestimate rather than overestimate the potential impacts of climate change.

In 2007, the IPCC shared the Nobel Peace Prize with environmental activist and former United States Vice President Al Gore.

How are scientists selected to contribute to the report?

The IPCC received approximately 3,000 author nominations for its Fifth Assessment Report from experts, organizations and governments around the globe. In May 2010, at a meeting in Geneva, the selected authors and review editors for the three working groups were announced. Lead authors for the reports are selected by elected members of the IPCC's Task Force Bureau, and all of the report's contributing authors are volunteers.

In total, there are 831 experts from 85 countries who are contributing to the IPCC's Fifth Assessment Report, and they represent a diverse range of fields, including oceanography, economics, physics, meteorology and social sciences.

The IPCC received 50 percent more author nominations for its latest report than for the previous report published in 2007. Additionally, 63 percent of the Fifth Assessment Report's authors are new to the IPCC process, according to the organization's website.

When will the IPCC release its new report?

The latest IPCC report will be released in stages, beginning this month. A Summary for Policymakers, based on the assessments of Working Group I, will be distributed on Sept. 27. The IPCC has also tentatively scheduled to release draft chapters from the Working Group I report online on Sept. 30.

While these dates may change, the Working Group II report, which focuses on socioeconomic impacts of climate change, is expected to be released in March 2014. The Working Group III report, which highlights possible solutions, is scheduled to be released in April 2014. The IPCC's Synthesis Report, which will incorporate findings from all the sections, is expected to be complete in October 2014.

What can we expect from the report?

At this point, it is difficult to know precisely what will be contained in the IPCC's Fifth Assessment Report, but some climatologists not involved with the organization have made predictions based on the scope of recent peer-reviewed climate research.

The IPCC's latest report will likely not have any startlingly new findings. Instead, the assessment will confirm many previous studies, but may increase levels of certainty surrounding some climate change issues, including the role of human activity in global warming, said Heidi Cullen, vice president and chief climatologist for Climate Central, a nonprofit science journalism organization based in Princeton, N.J.

"Science is more certain than ever that the majority of the warming since 1950 has indeed been caused by human activity — burning fossil fuels, coal, oil and gas," Cullen told reporters in a news briefing on Sept. 13.

The last IPCC report, published in 2007, said that it was "very likely" that human-induced greenhouse gas emissions caused more than half of the observed warming. Since the IPCC's assessment reports are meant to be comprehensive and are geared toward policymakers, the language used by the scientists tends to be more general.

Typically, the word "likely" corresponds to between 66 percent and 90 percent certainty, and "very likely" corresponds to at least 90 percent certainty, Cullen explained.

Other findings that will likely be revealed in the IPCC's new report include:

-Ice sheets and glaciers are melting faster than had been predicted in the 1990s.

-Ocean acidification is increasing due to excess amounts of carbon dioxide in the atmosphere.

-Arctic sea ice is retreating faster than had been estimated in the previous IPCC report.

-Surface warming has slowed in the past decade, which research has indicated may be due to natural ocean heat cycles or the emission of light-blocking aerosols.

-Sea levels have risen almost twice as fast from 1993 to 2010, compared with the amount of sea level rise recorded from 1901 to 2010. 

How does the IPCC reach their conclusions?

IPCC report authors comb through published, peer-reviewed research to assess the scope and impact of climate change. The IPCC includes all relevant scientific information, and clearly identifies disparate views with all the relevant scientific and technical support.

Priority is given to peer-reviewed studies, but authors may include information from government and industry reports if it helps to expand the breadth and depth of the assessment, according to the IPCC.

"Use of this literature brings with it an extra responsibility for the author teams to ensure the quality and validity of cited sources and information," IPCC officials said on the organization's website.

Once drafts of the report are written, there are typically three steps to the IPCC's review process, beginning with a 6- to 8-week period of expert analysis.

During this time, the selected authors put together a draft of their working group report, which is sent out to experts for review. After the resulting comments have been addressed, the authors put together a second draft that is edited by experts and governments. A final review of the report's Summaries for Policymakers, overview chapters and final Synthesis Report is conducted by government officials before the assessment is approved.

"Review is an essential part of the IPCC process to ensure objective, unbiased, transparent and comprehensive assessment of current scientific technical information," IPCC officials said.

Follow Denise Chow on Twitter @denisechow. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.

This week, federal climate scientists made it official: 2012 smashed the record for the hottest year in the United States. And now researchers warn that Americans can expect to see increasingly warm years ahead due to the effects of climate change.  

The U.S. Global Change Research Program released its draft National Climate Assessment Friday (Jan. 11), revealing the current understanding of climate-change science, how climate change is impacting Americans and what the country's climate might look like in the decades to come.

A warming planet, the report finds, is already affecting Americans' livelihoods and health, something that will intensify in the future.

"This could help restart a national conversation about climate change," Todd Sanford, a climate scientist with the science-policy nonprofit Union of Concerned Scientists (UCS), said in a statement. "It gives us a road map for climate change. And the road is much bumpier if we continue along a higher emissions pathway."

About 240 individuals contributed to the report and included scientists and individuals from local, state and federal government, the private sector and nonprofit organizations.

The resulting draft notes that the average temperature in the United States has increased by about 1.5 degree Fahrenheit since 1895, with more than 80 percent of that change occurring since 1980. The next few decades are projected to see another 2 to 4 degrees F of warming in most areas of the country, the draft says, while the amount of warming by the end of the century is projected to reach up to 5 to 10 degrees F if global emissions of greenhouse gases continue to increase at their current pace.

In this warmer future, people and livestock will have little respite from the heat, because nighttime temperatures will remain high, the draft says. And in other places, droughts will contribute to conditions that are driving larger and more frequent wildfires.

The report also warns that climate change is a public health concern as well.

"Climate change is increasing the risks of heat stress, respiratory stress from poor air quality, and the spread of waterborne diseases," the draft authors write. "Food security is emerging as an issue of concern, both within the U.S. and across the globe, and is affected by climate change."

Hurricane Sandy was an unfortunate reminder that infrastructure in the United States is vulnerable to extreme weather and the report highlights that roads, buildings, ports, and energy facilities are already being damaged by bigger storm surges caused by sea level rise.

Not only are the oceans rising, but also they're getting warmer. Increasing sea temperatures and acidification, combined with overfishing and pollution, could seriously hurt the fishing industry, the report reads.

"Climate change is already affecting us, and there's a growing demand at the local level for information about what it means for our present and our future," Sanford said in a UCS statement. "The climate conversation always starts with science. Because policymakers have generally supported policies that increase emissions, successfully adapting to climate change is becoming more difficult."

The draft, which has been submitted for public comment and will not be finalized for months, draws on scientific peer-reviewed research, including assessments by the United Nations Intergovernmental Panel on Climate Change (IPCC).

New satellite measurements suggest that global sea levels are rising faster than the most recent projections by the United Nations' climate change panel.

The new report found that sea levels are rising at an annual rate of 0.12 inches (3.2 millimeters) — 60 percent faster than the best estimate of 0.08 inches (2 millimeters) per year, which the Intergovernmental Panel on Climate Change (IPCC) calculated in 2007.

"This study shows once again that the IPCC is far from alarmist, but in fact has underestimated the problem of climate change," German oceanographer and climatologist Stefan Rahmstorf, who led the study, said in a statement. "That applies not just for sea-level rise, but also to extreme events and the Arctic sea-ice loss."

Satellites, which measure changes in sea level by bouncing radar waves off the sea surface, provide much more accurate measurements than tide gauges, because they have near-global coverage, as opposed to just coastal coverage, researchers say.

In addition to the change in sea level, the team assessed another marker of global warming — the overall warming trend of global temperatures. But their results closely corresponded with the IPCC's fourth assessment report, finding that the current overall warming trend of global temperatures is 0.28 degrees Fahrenheit (0.16 degrees Celsius) per decade.

Seas-level rise is thought to be driven by glacier melt as well as a phenomenon known as thermal expansion, which occurs when ocean water expands as it warms. Rising tides are a concern because they boost the threat of extreme flooding in populous coastal areas, putting millions of people at risk worldwide. The IPCC estimated the seas would rise up to an average of 6.6 feet (2 meters) by 2100, though some areas are expected to be hit harder than others.

The team involved in the new study included scientists from the Potsdam Institute for Climate Impact Research, the consulting firm Tempo Analytics and the French Laboratoire d'Etudes en Géophysique et Océanographie Spatiales (LEGOS).

Their findings appear today (Nov. 28) in the journal Environmental Research Letters, as delegates from 190 countries meet in Doha, Qatar, this week for the U.N.'s Climate Change Conference. The IPCC's next comprehensive report on the state of climate change is due out by 2014.

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Most of us have heard the predictions: the meltdown of Arctic sea ice and mountain-top glaciers; extinction of species ranging from polar bears to coral reefs; catastrophic sea level rise that could eventually force the relocation of millions of coastal residents. Heat waves, malnutrition and famine, and wildfires would also be a greater risk to human communities if carbon dioxide levels in Earth's atmosphere are allowed to rise too high.

Specifically, these could be the characteristics of a world where carbon dioxide has risen to 1,000 parts per million by 2100, as described this week in a Nature opinion essay by Stephen Schneider of Stanford University. (Currently carbon dioxide is at about 384 parst per million.)

Reaching this level of carbon dioxide by the end of the century was presented as a worst-case scenario if nothing is done to curtail emissions in a 2000 special report by the Intergovernmental Panel on Climate Change (IPCC).

But "it's not the worst-case scenario," Scheider now argues. "The worst-case scenario could be worse."

Until the economic downturn late last year, actual emissions have been higher than those in the IPCC scenario. So without any mitigation, "that's the track we're on now," Schneider told LiveScience.

Schneider doesn't think emissions will continue on this path, however: "I don't think the world is going to be that stupid for most of the century," he said.

Eventually, as we see more of the effects of warming, Schneider thinks that people will be galvanized into action and begin implementing cleaner technologies and cutting emissions.

But that still leaves the question of how much to cut them by. Two new studies, in the same issue of Nature, hope to clear the air by finding a different way to ask the question: "How much carbon is too much?"

Total carbon

The potentially drastically different world that awaits us if global warming continues unabated is something scientists have been warning about for decades now. The solution has also long been clear: Curb carbon dioxide and other greenhouse gas emissions.

But finding an agreement among the world's governments on how to go about cutting emissions, how soon to cut them, and how much to cut them by has been a much more challenging task.

Having a better understanding of what kind of emissions reductions are needed is particularly important with new negotiations this year to extend and amend the Kyoto Protocol, an agreement between nations to reduce emissions that is set to expire in 2012 (one that the United States never signed).

At the Earth Summit, held in Rio de Janeiro in 1992, 192 nations agreed to "to achieve stabilization of greenhouse gas concentrations in the atmosphere at a low enough level to prevent dangerous anthropogenic interference with the climate system."

Scientists "have been preoccupied ever since in trying to decide what that level is," said Myles Allen of Oxford University, and lead author of one of the new studies. Most countries have proposed either stabilizing emissions to achieve a certain carbon dioxide concentration in the atmosphere, or curbing emissions to stay under a maximum number of degrees of warming.

But under those frameworks, "you'd never really know what it was you were allowed to emit," said Gavin Schmidt of NASA's Goddard Institute for Space Studies in New York. Schmidt, who was not involved with the two new studies, wrote an accompanying editorial piece in same issue of the journal.

Given uncertainties in the climate system, figuring out how much warming would actually occur has proven difficult.

Simpler than expected?

So Allen and his colleague and Malte Meinshausen of the Potsdam Institute for Climate Impact Research in Germany and his colleagues took a different approach: Using computer models of various emissions scenarios and climate factors, they estimated the total amount of carbon that could be emitted and keep the world from going over 2 degrees Celsius (3.6 degrees Fahrenheit) of warming above pre-industrial levels (a goal adopted by many countries), which is just a 1.2 degrees C rise from today.

The upshot: "It's neither worse nor better than we thought, but the crucial message is it may be simpler than we thought," Allen said during a press briefing.

The studies found that we can only emit 1,000 billion tonnes (1,100 tons) of carbon dioxide between 2000 and 2050 to keep our chance of going over the 2 degree C limit by 2100.

That may seem like a lot of carbon, but that's only one quarter of the known economically recoverable fossil fuel reserves. And the world has already emitted one third of that budget in just nine years.

"If we continue burning fossil fuels as we do, we will have exhausted the carbon budget in merely 20 years, and global warming will go well beyond 2 degrees," Meinshausen said.

Put another way by Allen, a total emission of one trillion tones (1.1 trillion tons) of carbon over the entire period from 1750 to 2500 would likely cause a peak warming of 2 degrees C. About half of that has already been emitted since industrialization began.

"It took 250 years to burn the first half trillion tones and on current trends, we'll burn the next half trillion in less than 40," Allen said.

(The studies use different units and different base periods, which is why their numbers are different.)

What the studies effectively show is that it's the total amount of carbon emitted, not the pace or timing of emissions that determine most of the warming response.

"Mother Nature doesn't care about dates," Allen said. "To avoid dangerous climate change, we will have to limit the total amount of carbon we inject into the atmosphere, not just the emission rate in any given year."

Schmidt cautions, though, that the 2-degree limit is not a magic number that we are "safe" below or in danger above. He thinks of the 2 degrees Celsius of warming proposed by many countries as "a speed limit on the situation," he told LiveScience. It lets you know when you're going too fast and might be in danger of a crash, but you could still have an accident at a slower speed.

Policy plans

While the idea that it's the total amount of carbon that ultimately determines the total amount of warming isn't new, this is the first time it's been used to frame the emissions reduction question. Allen, Meinshausen and their colleagues hope that it will give policy makers a clearer picture of the situation and a better basis for determining how to make reductions.

"By treating the effective 'CO2 capacity' of the atmosphere as an exhaustible resource, we could provide governments and industry with simple, clear, and tractable guidance for long term planning," said David Frame, also of Oxford University and a co-author of Allen's study.

Schmidt took the data from the studies and looked at the total emissions that would occur if all developed countries adopted the plan proposed by President Obama to lower emissions 80 percent by 2050. If this happened, the world would have a roughly 50/50 chance of staying under the 2 degree benchmark, Schmidt said.

He noted that this framing could help policy makers see that "if you do all these things, it will make a difference. In fact, it will make the difference." (A common objection to the Kyoto Protocol was that its requirements would have little effect on warming trends.

Meinshausen's team is slated to discuss their findings with Germany's Chancellor Angela Merkel. Allen's team has also talked to economists and works with the UK Climate Change Committee, which advises Parliament.

Schneider agrees that the approach is useful for policy, but thinks that it shouldn't be necessary to persuade people that the climate risks are high enough that we need to act. The probability of the catastrophic outcomes he described in his essay coming to pass are between 5 and 10 percent, he wrote. This is far below the 1 to 2 percent chance of having a fire in your house, "yet we buy insurance because of the consequences of the outcome," he said.

But the next step is largely in the hands of governments and other policy makers, who will have to decide and how they want to make emissions reductions.

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Washington, D.C., and other coastal U.S. cities could find themselves under several more feet of water than previously predicted if warming temperatures destroy the West Antarctic Ice Sheet, a new study based on a model predicts.

The West Antarctic Ice Sheet (WAIS) towers about 6,000 feet (1,800 meters) above sea level over a large section of Antarctica. It holds about 500,000 cubic miles (2.2 million cubic kilometers) of ice, about the same amount of ice contained in the Greenland Ice Sheet.

This vast swath of ice is the anchor for numerous glaciers that drain into the polar sea and is bounded by the Ross and Ronne Ice Shelves. Whether or when this ice sheet might melt is still very uncertain, but even a partial melt would have a bigger impact on some coastal areas than others.

The new research found that sea level rise would not be uniform around the globe, owing to odd gravitational effects and predicted shifts in the planet's rotation.

Collapse concern

Throughout hundreds of millions of years in Earth's past, polar ice caps have grown and receded in cycles lasting thousands or even hundreds of thousands of years. When caps melted, seas rose.

What's different today is that melting of ice at both poles is occurring faster than what has naturally occurred in the past.

Some scientists are worried that our current path of warming could cause the collapse of all or part of the WAIS over the coming decades or centuries. These worries have been further fueled by a recent study in the journal Nature that indicates that more of the WAIS is warming than was previously thought.

"The West Antarctic is fringed by ice shelves, which act to stabilize the ice sheet — these shelves are sensitive to global warming, and if they break up, the ice sheet will have a lot less impediment to collapse," said co-author of the new study Jerry Mitrovica of the University of Toronto and the Canadian Institute for Advanced Research.

In its most recent report, released in 2007, the Intergovernmental Panel on Climate Change (IPCC) estimates that a full collapse of the ice sheet would raise sea levels by 16 feet (5 meters) globally.

Mitrovica and his colleagues say that this is an oversimplification, and that sea level rise will be higher than expected, and greater in some places than in others.

In particular, the researchers say, the IPCC estimate ignores three important effects of such a massive ice melt:

• Gravity: Like planets and other cosmic bodies that exert a gravitational pull on each other, huge ice sheets exert a gravitational pull on the nearby ocean, drawing water toward it. If an ice sheet melted, that pull would be gone, and water would move away. In the case of the WAIS, the net effect would be a fall in sea level within about 1,200 miles (2,000 km) of the ice sheet and a higher-than-expected rise in sea levels in the Northern Hemisphere, further away.
• Rebound: The WAIS is called a marine-based ice sheet because the weight of all that ice has depressed the bedrock underneath to the point that most of it sits below sea level. If all, or even some, of that ice melts, the bedrock will rebound, pushing some of the water on top of it out into the ocean, further contributing to sea level rise.
• Earth's rotation: A collapse of the WAIS would also shift the South Pole location of the Earth's rotation axis (an imaginary line running through the Earth from pole to pole) —about 1,600 feet (500 meters) from its present location. This would shift water from the southern Atlantic and Pacific oceans northward toward North America and the southern Indian Ocean.

Mitrovica and his fellow researchers took these effects into account and came up with a new projection of what would happen across the world if the WAIS melted out. Their findings are detailed in the Feb. 6 issue of the journal Science. "The net effect of all of these processes is that if the West Antarctic Ice Sheet collapses, the rise in sea levels around many coastal regions will be as much as 25 percent more than expected, for a total of between 6 and 7 meters [20 to 23 feet] if the whole ice sheet melts," Mitrovica said. "That's a lot of additional water, particularly around such highly populated areas as Washington, D.C., New York City, and the California coastline." Submerging threat Six meters of sea level rise would eventually inundate the nation's capital, because even though it doesn't have an extensive coastline, it was originally a low-lying, swampy area connected to the Chesapeake Bay. It would also put virtually all of south Florida and southern Louisiana underwater. The West Coast of North America, Europe and coastal areas around the Indian Ocean would all be inundated more than previously expected. The impact of the additional sea level rise can be seen on this interactive map. "We aren't suggesting that a collapse of the West Antarctic Ice Sheet is imminent," said study co-author Peter Clark of Oregon State University. "But these findings do suggest that if you are planning for sea level rise, you had better plan a little higher." The study was funded by the Canadian Institute for Advanced Research, the Natural Sciences and Engineering Research Council of Canada, the John Simon Guggenheim Memorial Foundation and the U.S. National Science Foundation.

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Claims are floating around the blogosphere that the American Physical Society, the leading professional organization for physicists, has reversed its position on global warming. But on its Web site, the APS has reaffirmed that it supports the consensus view that human-caused greenhouse gas emissions are warming the planet. Part of the statement the society adopted on Nov. 18, 2007, states: "Emissions of greenhouse gases from human activities are changing the atmosphere in ways that affect the Earth's climate." Stories of the supposed policy reversal began popping up after an article by Christopher Monckton, a politician and a former policy advisor in Margaret Thatcher's administration, submitted an article in an online newsletter of the APS Forum on Physics and Society. The article claimed that the Intergovernmental Panel on Climate Change (IPCC) had overestimated the Earth's climate sensitivity to carbon dioxide (or how much the global average temperature will change given a certain amount of carbon dioxide entering the atmosphere). In the article, Monckton, the 3rd Viscount Monckton of Brenchley, also claims that changes in solar activity are behind the warming trend of the past few decades, an idea that has been refuted by several climate scientists. A note in red lettering above the article states that it has not been peer-reviewed and that "its conclusions are in disagreement with the overwhelming opinion of the world scientific community. The Council of the American Physical Society disagrees with this article's conclusions." On their homepage, the APS has now placed a statement that reaffirms its 2007 position statement on global warming, which also states, "The evidence is incontrovertible: Global warming is occurring." It adds that mitigation efforts must be taken immediately.

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The recovery of Earth's protective ozone layer, expected to heal gradually over the next half-century or so, may be good news for your skin, but it could also put the brakes on a fast-moving wind current, further exacerbating global warming, a new study suggests. The ozone layer protects Earth's inhabitants from harmful ultraviolet rays, which can cause skin cancer in humans as well as mutations in other organisms. This layer sits in the lower portion of the stratosphere, the layer of the atmosphere above the troposphere, where Earth's weather occurs (and we live). Ozone absorbs the sun's UV light here before it can reach the planet's surface. The gaping hole in the ozone layer was discovered in 1985, eventually leading to the signing of the Montreal Protocol in 1987, which moved to ban the substances, such as chlorofluorcarbons (CFCs), which destroy stratospheric ozone. (The hole isn't a total absence of ozone, but a severe reduction in the concentration of ozone that occurs seasonally.) The new study, detailed in the June 13 issue of the journal Science, compares current climate models used by the International Panel on Climate Change to predict the potential long-term consequences of global warming to another set of models that better account for chemical reactions in the stratosphere. Study leader S-W. Son, of Columbia University in New York, and an international team of scientists found that the IPCC models fail to adequately model ozone recovery and its possible consequences. The other set of models they used showed that the healing of the ozone layer will warm the stratosphere, disrupting an important westerly wind jet closer to Earth's surface. This jet would slow near the South Pole, which could affect surface temperatures, the extent of sea ice, storm tracks, the location of arid regions and wind-driven ocean circulation in the Southern Hemisphere, the authors of the study said. Another recent study , detailed in the April 26 issue of the journal Geophysical Research Letters, also found that the recovery of the Antarctic ozone hole would warm up the atmosphere, subjecting the southernmost continent to the full effects of the warming pattern already affecting the rest of the world.

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Arctic sea ice is melting at a significantly faster rate than projected by even the most advanced computer models, a new study concludes.

"While the ice is disappearing faster than the computer models indicate, both observations and the models point in the same direction: The Arctic is losing ice at an increasingly rapid pace and the impact of greenhouse gases is growing," said study team member Marika Holland of the National Center for Atmospheric Research.

Holland and her colleagues compared model simulation of past climate with observations by satellites and found that the models simulated a loss in September ice cover of 2.5 percent per decade from 1953 to 2006. (September marks the yearly minimum in Arctic ice cover.)

While the highest rate of decline in any of the models was 5.4 percent per decade, satellite measurements, which are considered more reliable, showed that September ice actually declined at a rate of about 7.8 percent per decade during the same period.

"This suggests that current model projections may in fact provide a conservative estimate of future Arctic change, and that the summer Arctic sea ice may disappear considerably earlier than IPCC [Intergovernmental Panel on Climate Change] projections," said study team member Julienne Stroeve of the National Snow and Ice Data Center.

The shrinking ice may actually be about 30 years ahead of model predictions, meaning the Arctic could be ice free in the summer earlier than the IPCC’s predicted timeframe of 2050-2100.

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Our planet and its inhabitants - including we humans - are in a precarious position as we approach Earth Day, April 22.

While global warming is widely accepted as a reality by scientists and many governments and industrial leaders, progress to curb greenhouse gases and other forms of pollution remains limited. The current economic climate will likely make pollution control efforts more difficult, analysts say.

Recent studies, as well as the 2007 report by the Intergovernmental Panel on Climate Change (IPCC) have pointed to some of the likely effects of uncurbed greenhouse gas emissions: rising global temperatures, rising sea levels, Arctic sea ice melt, the disappear of glaciers, epic floods in some areas and intense drought in others.

These effects are intensified when combined with other forms of pollution the world's rising population.

Humans will face widespread water shortages. Famine and disease will increase. Earth’s landscape will transform radically, with a quarter of plants and animals at risk of extinction.

While putting specific dates on these traumatic potential events is challenging, this timeline paints the big picture and details Earth's future based on several recent studies and the longer scientific version of the IPCC report. This timeline is an updated version of one first published by LiveScience in 2007.

2008

Arctic sea ice hits its second lowest summer ice extent on record (the lowest extent was in 2007). A massive chunk of ice breaks away from Greenland's Petermann Glacier. Several breakups of ice shelves in Antarctica are observed. (NSIDC; Jason Box, Ohio State University; ESA, NSIDC)

Global oil production peaks sometime between 2008 and 2018, according to a model by a Swedish physicist. Others say this turning point, known as "Hubbert’s Peak," won’t occur until after 2020. Once Hubbert’s Peak is reached, global oil production will begin an irreversible decline, possibly triggering a global recession, food shortages and conflict between nations over dwindling oil supplies. (Doctoral dissertation of Frederik Robelius, University of Uppsala, Sweden; report by Robert Hirsch of the Science Applications International Corporation)

The Bush Administration enacts changes to the Endangered Species Act that affect reviews of government projects.

Polar bears and beluga whales are placed on the Endangered Species List. Gray wolves are delisted in certain areas.

2009

The U.S. Environmental Protection Agency declares carbon dioxide and other heat-trapping gases to be pollutants under the Clean Air Act.

An ice bridge connected to the Wilkins Ice Sheet of Antarctica breaks apart.

Many of the world's major rivers are found to be losing water. (Aiguo Dai, NCAR, Journal of Climate)

2012

The first phase of the Kyoto Protocol, an international environmental treaty created to limit the production of greenhouse gases, expires. Nations will have to draw up and enact a succesor treaty to further limit emissions, should they choose to do so.

2020

Flash floods will very likely increase across all parts of Europe. (IPCC)

Less rainfall could reduce agriculture yields by up to 50 percent in some parts of the world. (IPCC)

World population will reach 7.6 billion people. (U.S. Census Bureau)

2030

Diarrhea-related diseases will likely increase by up to 5 percent in low-income parts of the world. (IPCC)

Up to 18 percent of the world’s coral reefs will likely be lost as a result of climate change and other environmental stresses. In Asian coastal waters, the coral loss could reach 30 percent. (IPCC)

World population will reach 8.3 billion people. (U.S. Census Bureau)

Warming temperatures will cause temperate glaciers on equatorial mountains in Africa to disappear. (Richard Taylor, University College London, Geophysical Research Letters:)

In developing countries, the urban population will more than double to about 4 billion people, packing more people onto a given city's land area. The urban populations of developed countries may also increase by as much as 20 percent. (World Bank: The Dynamics of Global Urban Expansion)

The Arctic Sea could be ice-free in the summer. (James Overland, NOAA, Muyin Wang, University of Washington, Geophysical Research Letters)

2050

The Group of Eight top industrial nations has endorsed cutting greenhouse gas emission in half by this year.

Small alpine glaciers will very likely disappear completely, and large glaciers will shrink by 30 to 70 percent. Austrian scientist Roland Psenner of the University of Innsbruck says this is a conservative estimate, and the small alpine glaciers could be gone as soon as 2037. (IPCC)

Ocean acidification could kill off most coral reefs. (Ken Caldeira, Carnegie Institution of Washington, Science)

At least 400 bird species could become endangered or extinct due to deforestation and climate change. (Walter Jetz, University of California, Davis, PLoS Biology)

In Australia, there will likely be an additional 3,200 to 5,200 heat-related deaths per year. The hardest hit will be people over the age of 65. An extra 500 to 1,000 people will die of heat-related deaths in New York City per year. In the United Kingdom, the opposite will occur, and cold-related deaths will outpace heat-related ones. (IPCC)

World population reaches 9.4 billion people. (U.S. Census Bureau)

Crop yields could increase by up to 20 percent in East and Southeast Asia, while decreasing by up to 30 percent in Central and South Asia. Similar shifts in crop yields could occur on other continents. (IPCC)

As biodiversity hotspots are more threatened, a quarter of the world’s plant and vertebrate animal species could face extinction. (Jay Malcolm, University of Toronto, Conservation Biology)

2070

As glaciers disappear and areas affected by drought increase, electricity production for the world’s existing hydropower stations will decrease. Hardest hit will be Europe, where hydropower potential is expected to decline on average by 6 percent; around the Mediterranean, the decrease could be up to 50 percent. (IPCC)

Warmer, drier conditions will lead to more frequent and longer droughts, as well as longer fire-seasons, increased fire risks, and more frequent heat waves, especially in Mediterranean regions. (IPCC)

2080

While some parts of the world dry out, others will be inundated. Scientists predict up to 20 percent of the world’s populations live in river basins likely to be affected by increased flood hazards. Up to 100 million people could experience coastal flooding each year. Most at risk are densely populated and low-lying areas that are less able to adapt to rising sea levels and areas which already face other challenges such as tropical storms. (IPCC)

Coastal population could balloon to 5 billion people, up from 1.2 billion in 1990. (IPCC)

Between 1.1 and 3.2 billion people will experience water shortages and up to 600 million will go hungry. (IPCC)

Sea levels could rise around New York City by more than three feet, potentially flooding the Rockaways, Coney Island, much of southern Brooklyn and Queens, portions of Long Island City, Astoria, Flushing Meadows-Corona Park, Queens, lower Manhattan and eastern Staten Island from Great Kills Harbor north to the Verrazano-Narrows Bridge. (NASA GISS)

2085

The risk of dengue fever from climate change is estimated to increase to 3.5 billion people. (IPCC)

2100

A combination of global warming and other factors will push many ecosystems to the limit, forcing them to exceed their natural ability to adapt to climate change. (IPCC)

Atmospheric carbon dioxide levels will be much higher than anytime during the past 650,000 years. (IPCC)

Ocean pH levels will very likely decrease by as much as 0.5 pH units, the lowest it’s been in the last 20 million years. The ability of marine organisms such as corals, crabs and oysters to form shells or exoskeletons could be impaired. (IPCC)

Thawing permafrost and other factors will make Earth’s land a net source of carbon emissions, meaning it will emit more carbon dioxide into the atmosphere than it absorbs. (IPCC)

Roughly 20 to 30 percent of species assessed as of 2007 could be extinct by 2100 if global mean temperatures exceed 2 to 3 degrees of pre-industrial levels. (IPCC)

New climate zones appear on up to 39 percent of the world’s land surface, radically transforming the planet. (Jack Williams, University of Wisconsin-Madison, Proceedings of the National Academy of Sciences)

A quarter of all species of plants and land animals—more than a million total—could be driven to extinction. The IPCC reports warn that current “conservation practices are generally ill-prepared for climate change and effective adaptation responses are likely to be costly to implement.” (IPCC)

Increased droughts could significantly reduce moisture levels in the American Southwest, northern Mexico and possibly parts of Europe, Africa and the Middle East, effectively recreating the “Dust Bowl” environments of the 1930s in the United States. (Richard Seager, Lamont Doherty Earth Observatory, Science)

2200

An Earth day will be 0.12 milliseconds shorter, as rising temperatures cause oceans to expand away from the equator and toward the poles, one model predicts. One reason water will be shifted toward the poles is most of the expansion will take place in the North Atlantic Ocean, near the North Pole. The poles are closer to the Earth’s axis of rotation, so having more mass there should speed up the planet’s rotation. (Felix Landerer, Max Planck Institute for Meteorology, Geophysical Research Letters)

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Greenhouse gas emissions in the United States may grow faster in the next 50 years than they have in the past 50, and higher energy prices will curb the problem better than technology, two economists say.

Despite many technological advances in the past half-century, the rates of growth of energy use and of greenhouse gas emissions have continued to rise (by about 2.2 and 1.6 percent per year respectively), despite the rising costs of energy, Richard Eckaus of MIT and Ian Sue Wing of Boston University found in a new study.

"We found that, in spite of increasing energy prices, technological change has not been responsible for much reduction in energy use, and that it may have had the reverse effect," Eckaus said.

Another recent study showed that carbon dioxide levels in the atmosphere were rising faster than expected because inefficient technologies were on the rise in developed countries such as China and because the natural mechanisms for sucking up and storing carbon, called carbon sinks, were essentially being exhausted.

In the new study, funded by the U.S. Department of Energy and the Harvard Kennedy School of Government in Massachusetts, Eckaus and Sue Wing examined the periods of 1958 to 1996 and 1980 to 1996 and then used computer models to project changes in the growth rates of both energy use and emissions from 2000 to 2050. Their findings, detailed in the November issue of the journal Energy Policy, showed that these rates may accelerate.

"The rates of growth could be higher by a half percent or more, which becomes significant when compounded over 50 years," Eckaus said.

The Intergovernmental Panel on Climate Change released a report this weekend that warned of the hazards that rising carbon dioxide levels will cause, noting that even if reductions are made, certain effects, such as sea level rise, will still occur.

Technological advances may not be a fix even though they have been looked to as a source of curbing emissions of carbon dioxide and other greenhouse gases, Eckaus said, citing the U.S. steelmaking industry as an example.

Though steelmakers' furnaces are now electrical, reducing coal use at the steel plant, some of the electricity that powers the furnaces is still generated by coal, resulting in more carbon dioxide emissions.

Instead of relying on technology to solve the global warming problem, governments should make energy more expensive, Eckaus advises.

"There is no 'a priori' reason to think technology has the potential for reducing energy use while meeting the tests of economics," he said. "It's politically unappetizing in the U.S., but in Europe, gas costs $6 a gallon. Make energy more expensive: People will use less of it."

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Earthquakes, volcanic eruptions, tsunamis and landslides are some of the additional catastrophes that climate change and its rising sea levels and melting glaciers could bring, a geologist says.

The impact of human-induced global warming on Earth's ice and oceans is already noticeable: Greenland's glaciers are melting at an increasing rate, and sea level rose by a little more than half a foot (0.17 meters) globally in the 20th century, according to the Intergovernmental Panel on Climate Change.

With these trends in ice cover and sea level only expected to continue and likely worsen if atmospheric carbon dioxide levels continue to rise, they could alter the stresses and forces fighting for balance in the ground under our feet—changes that are well-documented in studies of past climate change, but which are just beginning to be studied as possible consequences of the current state of global warming.

"Although they've described it in the past, nobody's thought about it in terms of future effects of climate change," said Bill McGuire of the University College London's Hazard Research Center.

McGuire's speculations of increased geological activity have not yet been published in a journal, but he has written an article about them published in the Guardian Unlimited.

Rebounding crust

One particular feature that can change the balance of forces in Earth's crust is ice, in the form of glaciers and ice sheets that cover much of the area around Earth's poles plus mountains at all latitudes. The weight of ice depresses the crust on which it sits.

As the ice melts, the crust below no longer has anything sitting on top of it, and so can rebound fairly rapidly (by geological standards). (This rebounding is actually occurring now as a result of the end of the last Ice Age: The retreat of massive ice sheets from the northern United States and Canada has allowed the crust in these areas to bounce back.)

Areas of rebounding crust could change the stresses acting on earthquake faults and volcanoes in the crust.

"In places like Iceland, for example, where you have the Eyjafjallajökull ice sheet, which wouldn't survive [global warming], and you've got lots of volcanoes under that, the unloading effect can trigger eruptions," McGuire said.

With the changing dynamics in the crust, faults could also be destabilized, which could bring a whole host of other problems.

"It's not just the volcanoes. Obviously if you load and unload active faults, then you're liable to trigger earthquakes," McGuire told LiveScience, noting that there is ample evidence for this association in past climate change events.

"At the end of the last Ice Age, there was a great increase in seismicity along the margins of the ice sheets in Scandinavia and places like this, and that triggered these huge submarine landsides which generated tsunamis," McGuire said. "So you've got the whole range of geological hazards there that can result from if we see this big catastrophic melting."

Roland Burgmann, a geologist at the University of California, Berkeley, agrees that changes in ice cover can have significant effects on the underlying crust, but says that more research needs to be done to determine the actual scale of the threat and where the effects are most likely to occur.

Water pressure

Ice melt can have an added consequence because all that melted ice has to go somewhere—namely, the ocean.

And ice melt won't be the only factor changing sea levels: as ocean temperatures rise, the water itself expands (a process called thermal expansion).

As all that extra water piles up, it could apply pressure to faults near coastlines.

"The added load of the water bends the crust, and that means that you tend to get tensional conditions in the upper part of the crust and compressional a bit lower down, just as if you bend a plank of wood or something," McGuire explained.

These compressional forces could push out any magma lying around underneath a volcano, triggering an eruption. (This mechanism is actually believed to be the cause of the seasonal eruptions of Alaska's Pavlof volcano, which erupts every winter when sea levels are higher.)

McGuire conducted a study that was published in the journal Nature in 1997 that looked at the connection between the change in the rate of sea level rise and volcanic activity in the Mediterranean for the past 80,000 years and found that when sea level rose quickly, more volcanic eruptions occurred, increasing by a whopping 300 percent.

If today's worst-case global warming scenarios of catastrophic melting of glaciers and ice sheets come to pass, sea levels could rise rapidly, wreaking all sorts of geological havoc "comparable with the most rapid increases in sea level that we've seen in the last 15,000 years," McGuire said.

Burgmann isn't too worried about sea level rise causing more earthquakes or volcanic eruptions though, noting that catastrophic rates of sea level rise in the future are uncertain and that the current rate of rise—about 0.12 inches per year (3 millimeters per year)—isn't enough to destabilize the crust.

"It would take a long time to add up to a significant amount," Burgmann said—so while it's an area of research to keep an eye on, it's unlikely to have any disastrous consequences, at least for now.

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Apparently, “don’t sweat the small stuff” doesn’t apply to sea-level rise due to global warming: Scientists have found that smaller glaciers and ice caps, not Earth's expansive polar ice sheets, could cause the majority of the rise due to melting by 2100.

The Antarctic ice sheet and Greenland ice sheet have held the focus of melt research, in part because of the enormous amount of ice they contain—Antarctica alone holds 90 percent of the Earth's ice and 70 percent of its fresh water.

"They do have so much more ice that if they were to disappear, it would be totally catastrophic for civilization today," said study team leader Mark Meier of the University of Colorado at Boulder. But, he added, "there is no way they could disappear quickly."

The ice sheets are more resistant because the thicker the ice, the longer it takes to melt. The massive, sometimes mile-thick ice sheets are well below freezing internally, and so it would take a long time for the extra heat from global warming to be conducted down into the center of the ice to melt the sheets, Meier explained.

However, other glaciers and ice caps in mountains can melt at a faster rate. They can also simply slip into the sea.

Snow vs. melt

As snow accumulates on the upper portions of a glacier, the ice thickens and begins to flow down. The rate of flow partly determines how fast the glacier melts.

With rising temperatures, the surface of the glacier melts faster, and the water created percolates down through the ice, making the bed of the glacier more slippery and causing the ice to flow faster.

"Faster flow means more ice discharged to the ocean, which will then melt," Meier explained.

Glaciers high in mountain ranges such as the Alps also melt by flowing in this way, and their melt water runs into rivers and eventually into the ocean.

IPCC's missing info

Meier and his colleagues emphasized these types of losses in their study, detailed in the July 19 online issue of the journal Science, because considerations of flow rates were largely absent from the Intergovernmental Panel on Climate Change's (IPCC) estimates.

In its recent report, the IPCC estimated that the sea level rise (due to ice melt and the thermal expansion of ocean water) could be 7 to 23 inches by the end of the century, while Meier and his colleagues determined that the rise could actually be as much as 3.9 to 9.8 inches due to melt from glaciers and ice caps alone—roughly 60 percent of the total sea level rise due to melting ice.

The total estimated rise would be even higher when outlet glaciers from ice sheets and thermal expansion were included.

"We think they very much under-predicted the amount of ice loss to the ocean, especially from the glaciers and ice caps," Meier said. "We're predicting that the amount of ice melt will equal or perhaps even exceed the total sea level rise they are predicting."

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From catastrophic sea level rise to jarring changes in local weather, humanity faces a potentially dangerous threat from the changes our own pollution has wrought on Earth’s climate. But since nothing in science can ever be proven with 100 percent certainty, how is it that scientists can be so sure that we are the cause of global warming?

For years, there has been clear scientific consensus that Earth’s climate is heating up and that humans are the culprits behind the trend, says Naomi Oreskes, a historian of science at the University of California, San Diego.

A few years ago, she evaluated 928 scientific papers that dealt with global climate change and found that none disagreed about human-generated global warming. The results of her analysis were published in a 2004 essay in the journal Science.

And the Intergovernmental Panel on Climate Change (IPCC), the National Academy of Sciences and numerous other noted scientific organizations have issued statements that unequivocally endorse the idea of global warming and attribute it to human activities.

“We’re confident about what’s going on,” said climate scientist Gavin Schmidt of NASA’s Goddard Institute of Space Science in New York.

But even if there is a consensus, how can scientists be so confident about a trend playing out over dozens of years in the grand scheme of the Earth's existence? How do they know they didn’t miss something, or that there is not some other explanation for the world’s warming? After all, there was once a scientific consensus that the Earth was flat. How can scientists prove their position?

Best predictor wins

Contrary to popular parlance, science can never truly “prove” a theory. Science simply arrives at the best explanation of how the world works. Global warming can no more be “proven” than the theory of continental drift, the theory of evolution or the concept that germs carry diseases.

“All science is fallible,” Oreskes told LiveScience. “Climate science shouldn’t be expected to stand up to some fantasy standard that no science can live up to.”

Instead, a variety of methods and standards are used to evaluate the viability of different scientific explanations and theories. One such standard is how well a theory predicts the outcome of an event, and climate change theory has proven to be a strong predictor.

The effects of putting massive amounts of carbon dioxide in the air were predicted as long ago as the early 20th century by Swedish chemist Svante Arrhenius.

Noted oceanographer Roger Revelle’s 1957 predictions that carbon dioxide would build up in the atmosphere and cause noticeable changes by the year 2000 have been borne out by numerous studies, as has Princeton climatologist Suki Manabe’s 1980 prediction that the Earth’s poles would be first to see the effects of global warming.

Also in the 1980s, NASA climatologist James Hansen predicted with high accuracy what the global average temperature would be in 30 years time (now the present day).

Hansen's model predictions are “a shining example of a successful prediction in climate science,” said climatologist Michael Mann of Pennsylvania State University.

Schmidt says that predictions by those who doubted global warming have failed to come true.

“Why don’t you trust a psychic? Because their predictions are wrong,” he told LiveScience. “The credibility goes to the side that gets these predictions right.”

Mounting evidence

Besides their successful predictions, climate scientists have been assembling a “body of evidence that has been growing significantly with each year,” Mann said.

Data from tree rings, ice cores and coral reefs taken with instrumental observations of air and ocean temperatures, sea ice melt and greenhouse gas concentrations have all emerged in support of climate change theory.

“There are 20 different lines of evidence that the planet is warming,” and the same goes for evidence that greenhouse gases are increasing in the atmosphere, Schmidt said. “All of these things are very incontrovertible.”

But skeptics have often raised the question of whether these observations and effects attributed to global warming may in fact be explained by natural variation or changes in solar radiation hitting the Earth.

Hurricane expert William Gray, of Colorado State University, told Discover magazine in a 2005 interview, "I'm not disputing that there has been global warming. There was a lot of global warming in the 1930s and '40s, and then there was a slight global cooling from the middle '40s to the early '70s. And there has been warming since the middle '70s, especially in the last 10 years. But this is natural, due to ocean circulation changes and other factors. It is not human induced.”

Isaac Newton had something to say about all this: In his seminal “Principia Mathematica,” he noted that if separate data sets are best explained by one theory or idea, that explanation is most likely the true explanation.

And studies have overwhelmingly shown that climate change scenarios in which greenhouse gases emitted from human activities cause global warming best explain the observed changes in Earth’s climate, Mann said—models that use only natural variation can’t account for the significant warming that has occurred in the last few decades.

Mythic ice age

One argument commonly used to cast doubt on the idea of global warming is the supposed predictions of an impending ice age by scientists in the 1970s. One might say: First the Earth was supposed to be getting colder; now scientists say it’s getting hotter—how can we trust scientists if they’re predictions are so wishy-washy?

Because the first prediction was never actually made. Rather, it’s something of an urban climate myth.

Mann says that this myth started from a “tiny grain of truth around which so much distortion and misinformation has been placed.”

Scientists were well aware of the warming that could be caused by increasing greenhouse gases, both Mann and Schmidt explained, but in the decades preceding the 1970s, aerosols, or air pollution, had been steadily increasing. These tiny particles tended to have a cooling effect in the atmosphere, and at the time, scientists were unsure who would win the climate-changing battle, aerosols or greenhouse gases.

“It was unclear what direction the climate was going,” Mann said.

But several popular media, such as Newsweek, ran articles that exaggerated what scientists had said about the potential of aerosols to cool the Earth.

But the battle is now over, and greenhouse gases have won.

“Human society has made a clear decision as to which direction [the climate] is going to go,” Mann said.

Future predictions

One of the remaining skeptics, is MIT meteorologist Richard Lindzen. While he acknowledges the trends of rising temperatures and greenhouse gases, Lindzen expressed his doubt on man’s culpability in the case and casts doubt on the dire predictions made by some climate models, in an April 2006 editorial for The Wall Street Journal.

“What the public fails to grasp is that the claims neither constitute support for alarm nor establish man's responsibility for the small amount of warming that has occurred,” Lindzen wrote.

To be sure, there is a certain degree of uncertainty involved in modeling and predicting future changes in the climate, but “you don’t need to have a climate model to know that climate change is a problem,” Oreskes said.

Climate scientists have clearly met the burden of proof with the mounting evidence they’ve assembled and the strong predictive power of global warming theory, Oreskes said-- global warming is something to pay attention to.

Schmidt agrees. “All of these little things just reinforce the big picture,” he said. “And the big picture is very worrying.”

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Global warming could turn the heat way up during the summer  in the eastern United States, raising the average by nearly 10 degrees Fahrenheit by the 2080s, a new NASA study finds.

“There is the potential for extremely hot summertime temperatures in the future, especially during summers with less-than-average frequent rainfall,” said lead author Barry Lynn of NASA’s Goddard Institute for Space Studies in New York City.

Summer’s daily high temperatures currently average in the low-to-mid 80s in the East, but global warming could cause those temperatures to soar into the low-to-mid 90s in the next 70 years.

During extreme summers, if less rain falls to cool the Earth, July and August highs could average between 100 and 110 degrees Fahrenheit in cities such as Chicago, Washington, D.C. and Atlanta.

Researchers analyzed nearly 30 years of observational temperature and precipitation data and used computer models to simulate changes in atmospheric circulation that could be used to predict variations in summer-to-summer temperatures.

The predictions were made assuming that carbon dioxide emissions continued to increase about 2 percent a year, known as the “business as usual” model. The findings, detailed in the April 2007 issue of the American Meteorological Society’s Journal of Climate, were too recent to be factored into the latest Intergovernmental Panel on Climate Change report.

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The same volcanic eruptions that sundered Greenland from Western Europe and created Iceland also triggered intense global warming 55 million years ago, scientists say.

“There has been evidence in the marine record of this period of global warming, and evidence in the geologic record of the eruptions at roughly the same time,” said study team member Robert Duncan, an oceanic scientist at Oregon State University, “but until now there has been no direct link between the two.”

During the Paleocene-Eocene Thermal Maximum (PETM), massive amounts of greenhouse gases were injected into the oceans and atmosphere, causing global sea surface temperatures to rise by up to 10 degrees Fahrenheit.

The event changed global rainfall patterns, broiled and acidified the oceans, and killed up to 50 percent of the world’s deep-sea organisms. The warm climate also opened up new migration routes for horses and other mammals into North America and might have even fueled early primate evolution.

The PETM took roughly 100,000 years to peak, and it was another 100,000 years or so before the climate recovered. What triggered the PETM has been a topic of intense speculation by scientists. Theories have ranged from the extensive burning of peat and coal deposits to an impact by a carbon-rich comet.

Matching ash

In the new study, detailed in the April 27 issue of the journal Science, the researchers linked the PETM to volcanic eruptions occurring from 55 to 61 million years ago. Back then, Greenland was still fused to Europe as part of one vast supercontinent, and the Northern Atlantic Ocean did not exist yet.

The team matched the chemical composition and deposition date of ash layers in East Greenland amassed during the peak of the eruptions with ash found in marine sediments in the Atlantic Ocean.

The scientists speculate magma and hot outgassing from the North Atlantic volcanism heated decaying organic material rich in carbon deposited in low-lying basins.

“The hot magma worked its way up through the crust and invaded these basins, essentially cooking all this stuff and liberating a lot more greenhouse gases than was actually coming from the magma itself,” Duncan explained.

Only a trigger

But the volcanism was only a trigger. All the greenhouse gas emitted by the eruptions and the ensuing cooking of organic matter would still not have been enough to cause the changes in climate and ocean chemistry seen during the PETM.

Other scientists have proposed the North Atlantic volcanism might have warmed the oceans enough to liberate methane trapped in icy sediments—called “methane hydrate”—on the ocean floor.

“Volcanism could have served as a trigger to start the system moving toward warmer temperatures,” said James Zachos, a paleo-oceanographer at University of California, Santa Cruz. “Then the ocean passes some threshold for hydrate stability, and the hydrate starts to decompose.”

Zachos, who was not involved in the new study, called the findings the most compelling evidence yet for explaining the PETM.

Volcanic activity similar to that implicated in the PETM still occurs in regions like Yellowstone National Park and the Galápagos and the Hawaiian Islands.

“These hotspots are part of the everyday world,” Duncan told LiveScience. “It’s just that we don’t have volcanic events as catastrophic as what [occurred] in the North Atlantic on a continual basis. Thank God too, because it would be a very different world.”

Today's global warming

Research on the PETM not only sheds light on Earth’s ancient climate, but also provides clues about the potential long-term consequences of our current global warming.

The PETM is “one of the few examples in the natural record where we get changes in chemistry and temperature that are approaching what we’re seeing today,” Duncan said.

The United Nations recently released an authoritative report that concluded human activity could cause atmospheric temperatures to rise up to 11 degrees Fahrenheit by the close of the century.

Our species might achieve in 100 years what took 100,000 years to happen naturally. And if the PETM is any indication, Duncan said, it will also take our planet about that long to recover.

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In the next two centuries, global warming could cause the days to grow slightly shorter on Earth, a new study finds.

Another effect of warming, however, might actually lengthen the day.

As ocean water gets warmer due to climate, seawater expands thereby raising sea levels and  changing the ocean’s circulation and even exerting more pressure on the ocean floor below in some areas, explained Jochem Marotzke of the Max Planck Institute in Germany.

These pressure changes won’t be uniform across the globe, because global warming will cause the ocean to warm more in some places than in others.

But over time, the differences will redistribute Earth’s ocean water, pushing it away from deep waters and onto shallower coastal shelf areas, primarily toward the North Pole.

Marotzke and colleagues, whose new study is detailed in the March 28 issue of the journal Geophysical Research Letters, used ocean conditions predicted in the latest report of the Intergovernmental Panel on Climate Change to model how ocean pressure would change as sea level rises.

Like the physics behind a figure skater pulling in her arms to cause a  faster spin, the pressure transfer would shift the ocean’s mass toward Earth’s axis of rotation,Marotzke said. As the mass shifted, the Earth would spin around faster, shortening the length of the day by about 0.12 milliseconds (about 1/500th of the blink of an eye) by the year 2200.

“Which, of course, is completely unnoticeable in everyday life,” Marotzke said, so the change in day won’t affect humans. The connection between global warming and length of the day was interesting because it was so unexpected, he said.

It's not clear, however, whether you might actually have less time or more time to ponder all this.

Other research suggests a warmer atmosphere would create stronger winds and actually slow the Earth down, causing the planet to spin slightly more slowly and therefore lengthening the day.

Other factors such as the drift of the Moon away from the Earth, weather and perhaps changes in Earth’s interior also imperceptibly change the speed of the planet’s rotation.

An MIT meteorologist said three years ago that he would bet money that global average temperatures would cool back down in 20 years. The quote triggered a flurry of Internet dialogues and prompted scientists to challenge each other to make bets on climate-change issues.

One scientist took the wagering meteorologist, Richard Lindzen, up on his bet, but the deal fell apart over a disagreement about odds.

Now, an online gambling service is giving the public a chance to do what scientists have been doing among themselves for years. The service, BetUS.com, announced it will give members a chance to wager on various global warming-related issues.

But scientists warn the odds are designed to part suckers from their cash.

Pop culture gaming

BetUS.com spokesman Reed Richards said the company will personally back numerous bets, or “propositions,” posted on the website related to global warming.  “It’s part of a campaign we’ve been doing for the past two and a half years called ‘pop culture gaming,’” Richards said. “You can wager on things in the headlines.”

One bet gives members 1-to-5 odds that scientists will prove global warming exists beyond any scientific doubt by the end of this year. Another gives 100-to-1 odds that polar bears will be extinct by 2010. (A complete list of all the global-warming related bets is listed at the end of this article.)

Richards said “thousands” of people have already placed money on the company’s global-warming bets, with $10 being the average wager.

A dozen analysts combed through scientific studies on global warming to create the odds, Richards said.

“This is where the advantage is to the player,” Richards said in a telephone interview. “Unlike sports, where there are set formulas and statistics and numbers, these are variables that we can’t anticipate.”

A risky wager

Climate scientists disagree that the public has the upper hand. Gavin Schmidt, a climate modeler at NASA’s Goddard Institute for Space Studies (GISS) in New York, said the bets are “designed to part fools from their money.”

For example, one of the bets the website offers is 150-to-1 odds that the oceans will rise six inches on average worldwide by the end of the year. “It’s more like a billion to one,” Schmidt told LiveScience. “Anyone who puts money on that would be an idiot.”

Another bet for the taking has odds of 100-to-1 that Manhattan will be under water by 2012. “Do they have any idea how high the peak of Manhattan is?” Schmidt said. (The highest natural point in Manhattan is 265 feet above sea level)

James Annan, a climate scientist at the Frontier Research Center for Global Change in Japan, said many of the bets are “silly” and mostly of the “Elvis will be found alive and living on the Moon” type.

However, there is one bet Annan said he might consider. BetUS.com is offering odds of 300-to-1 that humans will find a way to reverse global warming so efficiently that global freezing becomes a factor by 2020.

“This is really more technological and political speculation than climate science,” Annan said. For example, scientists could achieve this chilling effect by injecting enough sun-blocking dust into the atmosphere or placing a large sunshade in space.

 “300-to-1 might make this worth considering, I suppose,” Annan said.

Scientists do it

While new to most of us, betting on global warming is old hat to some scientists.

In 2005, Annan offered to take Lindzen, the MIT meteorologist, up on his bet that global temperatures in 20 years will be cooler than they are now. However, no wager was ever settled on because Lindzen wanted odds of 50-to-1 in his favor. This meant that for a $10,000 bet, Annan would have to pay Lindzen the entire sum if temperatures dropped, but receive only $200 if they rose.

“Richard Lindzen’s words say that there is about a 50 percent chance of [global] cooling,” Annan wrote about the bet. “His wallet thinks it is a 2 percent shot. Which do you believe?”

Soon after, however, Galina Mashnich and Vladimir Bashkirtsev, two Russian solar physicists who argue global temperatures are driven by changes in the Sun’s activity, agreed to Annan’s bet.

The two camps have agreed to compare global temperatures between 1998 and 2003 with those between 2012 and 2017. The loser will pay up in 2018.

Since 2005, Annan said he has offered to make bets with other global warming skeptics. “There have been a few nibbles since but nothing substantial has turned up,” Annan said in an email interview.

Few climate scientists seem willing to bet against the effects of global warming. “A couple of colleagues have offers on the table, but there are no takers on the other side,” he added.

A measure of truth

Schmidt said betting on global warming is a good measure of a global warming nay-sayer’s conviction.

“Most people who claim to be contrarians and say the planet is going to cool, none of them will put their money where their mouth is,” he said. “It’s been a very good way of showing that a lot of the noise that you hear from the wackier elements is in fact just noise and actually is not based on anything.”

Schmidt described one bet he personally negotiated with a Canadian paleo-climatologist one night over a dinner that included wine.

“I said it will warm more than 0.1 degree [Celsius] in the next decade. He said it would warm less than that,” Schmidt said. “But then in the morning, when he may have sobered up, and I tried to get a confirmation that was the bet that we had, I heard no more.”

Global Warming Related Bets Offered by BetUS.com (see notes below regarding * and #):

• It's proven that global warming exists beyond any scientific doubt before Dec. 31, 2007 Yes - 1/5* #
• It's proven that humans caused global warming beyond any scientific doubt before Dec. 31, 2007 Yes - 2/1*#
• The ocean will rise six inches by the end of the year (worldwide as an average) Yes - 150/1
• Polar Bears will become extinct by 2010 Yes - 100/1
• A car that runs solely on water will hit the market by 2008 (must be a stock car produced for mass consumption) Yes - 150/1
• Antarctica will become livable for humans by 2015 (must be able to sustain crops in order for wager to win) Yes - 500/1
• Humans will find a way to reverse global warming so efficiently that global freezing becomes a factor by 2020 Yes - 300/1
• Manhattan will be under water before 12/31/11 Yes - 100/1
• Florida will be under water before 12/31/11 Yes - 10/1     
• Cape Cod is submerged by 2015 Yes - 150/1
• Cape Hatteras is submerged by 2015 Yes - 300/1
• Cape Canaveral is submerged by 2015 Yes - 100/1
• Cape Henry is submerged by 2015 Yes - 200/1
• Cape May is submerged by 2015 Yes - 200/1

*To qualify as proven, "the government would have to announce in a statement that the study is without flaw and also conclude it is real without any scientific doubt," BetUS.com spokesman Reed Richards said.

# Of these bets, James Annan said: “Under the definition of ‘the government says so,’ then we seem to be pretty much there, since the [U.S.] government has endorsed the IPCC report. ‘Beyond any scientific doubt’ is poorly worded though. I don’t expect anyone in any official position to use that exact form.”

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NEW YORK (AP) -- New York City produces nearly 1 percent of the nation's greenhouse gas emissions -- an amount that puts it on par with Ireland or Portugal -- according to a city study.

The study, released Tuesday, was ordered by Mayor Michael Bloomberg to assess the city's progress in reducing its greenhouse gas emissions by 30 percent by 2030. It was conducted by the mayor's Office of Long-term Planning and Sustainability.

"You have to have a real baseline or we're just talking past each other as to what works and what doesn't work -- we won't ever know whether we really made a difference,'' Bloomberg said.

The study found that the buildings, subways, buses, cars and decomposition of waste in America's most populous city produced a net emission of 58.3 million metric tons of greenhouse gases in 2005. The report said the city's emissions "are currently as much as those of Ireland or Portugal.''

The U.S. total was 7.26 billion metric tons for that year.

Greenhouse gases, including carbon dioxide, methane and other gases, essentially trap energy from the sun, which warms the Earth's surface and lower atmosphere. Many scientists believe human activity that increases those gases is contributing to global warming.

The Intergovernmental Panel on Climate Change, a United Nations network of 2,000 scientists, warned last week of possible catastrophic risks such as floods, disease, food shortages, species extinction and human suffering throughout the world.

The city has 2.7 percent of the country's population -- 8.2 million of 300 million -- and the average New York City resident contributes less than a third of the emissions generated by a typical American. This is largely due to the popularity of the city's mass transit system, which cuts down on car emissions, officials said.

The operation of the city's hundreds of thousands of buildings -- which consume electricity, natural gas, fuel oil and steam -- contribute 79 percent of the city's emissions total.

The study found that the city's focus on environmentally friendly initiatives -- including alternative fuel vehicles, energy efficient traffic lights and green buildings -- appears to have helped stabilize emissions rates in recent years.

"Each one of these things really does make a difference, and they add up,'' Bloomberg said.

Still, emissions were found to have increased by more than 8 percent between 1995 and 2005, the study found.

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Injecting carbon dioxide into wet, porous rocks deep underground may be a good way to reduce emissions of this major greenhouse gas because the rocks trap the gas better than previously thought, a new study claims.

For many years, scientists have looked into pumping carbon dioxide deep underground, where it could be stored for thousands of years, to reduce levels emitted from power plants. But many environmental groups oppose this process, known as carbon sequestration, because of the possibility that carbon dioxide could leak out.

Earlier this month, scientists who authored the latest Intergovernmental Panel on Climate Change report, which predicted the dire consequences and inevitable global warming, called for governments to take immediate action to curb carbon dioxide and other greenhouse gases that have contributed to climate change.

One of many methods

Scientists have explored numerous methods for reducing greenhouse gas emissions, including injecting sulfur into the air and placing a satellite shield around the Earth. Billionaire Richard Branson announced last Friday that he would give $25 million to any scientist who could come up with technology that would extract greenhouse gases from the atmosphere.

MIT researcher Ruben Juanes, author of the new study, says these methods need not compete with one another.

"Rather than comparing carbon sequestration with other alternatives," Juanes told LiveScience. "What I would say is that all of them at this point should be looked into and should be investigated seriously to really assess their full potential."

Underground storage

Scientists think that carbon dioxide could potentially be stored in three types of underground locations: depleted oil and gas fields, unminable coal seams and briny aquifers. For all these methods, a "geologic cap," usually a layer of largely impermeable rock, above the target area is needed to prevent leaks.

Saltwater aquifers are particularly attractive because they are ubiquitous underground, even far away from oceans, and offer more storage volume, but environmental groups are particularly nervous about leaks of carbon dioxide sequestered in aquifers because the buoyancy of the gas causes it to rise in the water.

These worries are unwarranted, according to the new study published in a recent issue of the journal Water Resources Research.

When carbon dioxide is injected into the porous rock saturated with salt water, it forms a plume and starts to rise through the rock. Because the rock minerals have an affinity for water, the water will coat the crevices and pore walls of the rock in a thin film, just as raindrops might spread out and form a film when they land on your skin.

When injection stops, the water closes up at the bottom of the plume, essentially turning it into a long bubble, Juanes said. The water films in the rock pores swell, eventually touching and closing off the carbon dioxide's escape.

"The plume of CO₂ that was sort of a continuous blob is now being chopped of into small blobs," Juanes explained. "And because these blobs are small, they don't have enough buoyancy to continue [their] vertical assent. So these blobs just remain there in the porous medium, trapped."

A viable option?

But whether sequestration is a viable means of curbing plant emissions remains to be seen; cost is an important factor in implementing the strategy because carbon dioxide has to be separated from a power plant's gas stream and compressed before it can be injected into the ground.

"There has to be some economic incentive or some regulatory structure to make that happen," Juanes said.

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WASHINGTON (AP)—Later this week in Paris, climate scientists will issue a dire forecast for the planet that warns of slowly rising sea levels and higher temperatures. But that may be the sugarcoated version.

Early and changeable drafts of their upcoming authoritative report on climate change foresee smaller sea level rises than were projected in 2001 in the last report. Many top U.S. scientists reject these rosier numbers. Those calculations don't include the recent, and dramatic, melt-off of big ice sheets in two crucial locations:

They "don't take into account the gorillas—Greenland and Antarctica,'' said Ohio State University earth sciences professor Lonnie Thompson, a polar ice specialist. "I think there are unpleasant surprises as we move into the 21st century.''

Michael MacCracken, who until 2001 coordinated the official U.S. government reviews of the international climate report on global warming, has fired off a letter of protest over the omission.

The melting ice sheets in Greenland and Antarctica are a fairly recent development that has taken scientists by surprise. They don't know how to predict its effects in their computer models. But many fear it will mean the world's coastlines are swamped much earlier than most predict.

Others believe the ice melt is temporary and won't play such a dramatic role.

That debate may be the central one as scientists and bureaucrats from around the world gather in Paris to finish the first of four major global warming reports by the Intergovernmental Panel on Climate Change. The panel was created by the United Nations in 1988.

After four days of secret word-by-word editing, the final report will be issued Friday.

The early versions of the report predict that by 2100 the sea level will rise anywhere between 5 and 23 inches. That's far lower than the 20 to 55 inches forecast by 2100 in a study published in the peer-review journal Science this month. Other climate experts, including NASA's James Hansen, predict sea level rise that can be measured by feet more than inches.

The report is also expected to include some kind of proviso that says things could be much worse if ice sheets continue to melt.

The prediction being considered this week by the IPCC is "obviously not the full story because ice sheet decay is something we cannot model right now, but we know it's happening,'' said Stefan Rahmstorf, a climate panel lead author from Germany who made the larger prediction of up to 55 inches of sea level rise. "A document like that tends to underestimate the risk,'' he said.

"This will dominate their discussion because there's so much contentiousness about it,'' said Bob Corell, chairman of the Arctic Climate Impact Assessment, a multinational research effort. "If the IPCC comes out with significantly less than one meter (about 39 inches of sea level rise), there will be people in the science community saying we don't think that's a fair reflection of what we know.''

In the past, the climate change panel didn't figure there would be large melt of ice in west Antarctica and Greenland this century and didn't factor it into the predictions. Those forecasts were based only on the sea level rise from melting glaciers (which are different from ice sheets) and the physical expansion of water as it warms.

But in 2002, Antarctica's 1,255-square-mile Larsen B ice shelf broke off and disappeared in just 35 days. And recent NASA data shows that Greenland is losing 53 cubic miles of ice each year—twice the rate it was losing in 1996.

Even so, there are questions about how permanent the melting in Greenland and especially Antarctica are, said panel lead author Kevin Trenberth, chief of climate analysis at the National Center for Atmospheric Research in Colorado.

While he said the melting ice sheets "raise a warning flag,'' Trenberth said he wonders if "some of this might just be temporary.''

University of Alabama at Huntsville professor John Christy said Greenland didn't melt much within the past thousand years when it was warmer than now. Christy, a reviewer of the panel work, is a prominent so-called skeptic. He acknowledges that global warming is real and man-made, but he believes it is not as worrisome as advertised.

Those scientists who say sea level will rise even more are battling a consensus-building structure that routinely issues scientifically cautious global warming reports, scientists say. The IPCC reports have to be unanimous, approved by 154 governments—including the United States and oil-rich countries such as Saudi Arabia—and already published peer-reviewed research done before mid-2006.

Rahmstorf, a physics and oceanography professor at Potsdam University in Germany, says, "In a way, it is one of the strengths of the IPCC to be very conservative and cautious and not overstate any climate change risk.''

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Hot Topic

Goldilocks and the Greenhouse What makes Earth habitable?

This LiveScience original video explores the science of global warming and explains how, for now, conditions here are just right.

The Controversy

• Global Warming or Just Hot Air? A Dozen Different Views
• Baffled Scientists Say Less Sunlight Reaching Earth
• Scientists Clueless over Sun's Effect on Earth
• Greenhouse Gas Hits Record High
• Key Argument for Global Warming Critics Evaporates

The Effects

• Seas Rise
• More Wildfires
• Deserts to Grow
• Greenland Melts
• Mountains Grow
• Ground Collapses
• Glaciers Disappear
• Allergies Get Worse
• Summer Gets Longer
• Animal DNA Changing
• Animals Change Behavior
• Rivers Melt Sooner in Spring
• Increased Plant Production
• Hurricanes Get Stronger
• Some Trees Benefit
• Lakes Disappear

The Possibilities

• More Rain but Less Water
• Ice-Free Arctic Summers
• Overwhelmed Storm Drains
• Worst Mass Extinction Ever
• A Chilled Planet

Strange Solutions

• Inject Sulfur into Air to Battle Global Warming
• Space Ring to Shade Earth
• Longer Airline Flights