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.
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Denise Chow was the assistant managing editor at Live Science before moving to NBC News as a science reporter, where she focuses on general science and climate change. Before joining the Live Science team in 2013, she spent two years as a staff writer for Space.com, writing about rocket launches and covering NASA's final three space shuttle missions. A Canadian transplant, Denise has a bachelor's degree from the University of Toronto, and a master's degree in journalism from New York University.