What is climate change, and how is it affecting Earth?

Image of a glacier in Jasper National Park in Canada that has retreated very far.
Human-caused climate change has resulted in record rates of glacial melting. This glacier and the marker of it's edge in 1908 is in Jasper National Park, Canada. (Image credit: Shutterstock)

Climate change is any long-term alteration in average weather patterns, either globally or regionally. Climate change has occurred many times in Earth's history, and for many different reasons. The changes in global temperature and weather patterns seen today, however, are caused by human activity. And they're happening much faster than the natural climate variations of the past. 

Scientists have many ways to track climate over time, all of which make it clear that today's climate change is linked to the emission of greenhouse gases, such as carbon dioxide and methane. These gases trap heat from the sun's rays near Earth's surface, much like the glass walls of a greenhouse keep heat inside. Small changes in the proportions of greenhouse gases in the air can add up to major changes on a global scale. 

On average, the effect of greenhouse gases is to increase global temperatures. This is why climate change is sometimes called global warming. However, most researchers today prefer the term climate change because of the variability of weather and climate across the globe. For example, warming global average temperatures might alter the flow of the jet stream, the major air current affecting North American weather, which could in turn lead to seasonal periods of extreme cold in some areas. 

"It's important for people to realize that there is a lot of variability from place to place on the Earth in terms of the temperature," said Ellen Mosley-Thompson, a paleoclimatologist at the Byrd Polar and Climate Research Center of The Ohio State University. "When we talk about global climate change, we're talking about temperature changes over large areas."

How do scientists know climate change is real?

The effects of global warming are visible. The climate of the past is recorded in ice, sediments, cave formations, coral reefs and even tree rings. Researchers can look at chemical signals — such as the carbon dioxide trapped in bubbles inside glacial ice — to determine what atmospheric conditions were like in the past. They can study microscopic fossilized pollen to learn what vegetation used to thrive in any given area, which in turn can indicate what the climate was like. Scientists can also measure tree rings to get a season-by-season record of temperature and moisture. Ratios of chemical variants of oxygen in corals and stalactites and stalagmites can reveal past precipitation patterns. 

Different types of natural records can reveal different clues about the climate of the past. Ocean sediments don't carry season-by-season or even year-by-year levels of detail, but they can provide blurrier pictures of climate dating back millions of years, Mosley-Thompson told Live Science. (The oldest cores drilled from ocean sediments date back 65 million years, according to The Smithsonian Institution.) Tree records are relatively short but incredibly detailed. And ice can be chock-full of information: Not only do glaciers capture atmospheric gases in the form of air bubbles, they trap dust and other sediments, pollen grain, volcanic ash and more. As the ice gets older and more compressed, the record can become fuzzy, Mosley-Thompson said, but newer ice can provide a year-by-year look at what the climate was doing. 

The most recent changes in the climate — since the beginning of the Industrial Revolution — have also been tracked directly. Record-keeping of things like land temperature began to improve in the late 1800s, and ship captains began to keep a wealth of ocean-based weather data in their logs. The advent of satellite technology in the 1970s provided an explosion of data, covering everything from ice extent at the poles to sea surface temperature to cloud coverage.

Overall, the Earth is warming up because of human-caused climate change. But climate change also causes seasonal periods of extreme cold. (Image credit: Shutterstock)

How is the climate changing?

Taken together, these records show that the modern climate is undergoing a swift departure from the patterns of the past.

Before the Industrial Revolution, there were about 280 carbon dioxide molecules for every million molecules in the atmosphere, or 280 parts per million (ppm). As of 2021, the global average level of CO2 was 419 ppm — more than 100 ppm higher than the level has been in the last 800,000 years, and up 6.5 ppm from 2020, according to the National Oceanic and Atmospheric Administration (NOAA). The last time atmospheric carbon reached today's levels was 3 million years ago, according to NOAA. 

The rate of change in today's atmospheric carbon is also faster than in the past, according to NOAA. The rate of increase was 100 times faster over the past 60 years than any time in the last million years or so — a period that saw eight major climate flip-flops between glacial cycles, in which ice expanded from the poles into the middle latitudes, and interglacial cycles, in which the ice retreated to where it is today. And the rate continues to increase. In the 1960s, atmospheric carbon went up by an average of 0.6 ppm a year. In the 2010s, it rose by an average of 2.3 ppm per year. 

The heat-trapping ability of all that extra carbon has translated to rising global average temperatures. According to NASA's Goddard Institute for Space Studies (GISS), Earth's average temperature has risen by just over 2 degrees Fahrenheit (1 degree Celsius) since 1880, a measurement accurate to within a tenth of a degree Fahrenheit. As with the rate of atmospheric carbon increase, the rate of global temperature increase is also speeding up, according to NASA's Earth Observatory: Two-thirds of the warming that’s taken place since 1880 has occurred since 1975.

What are the impacts of climate change?

This warming has caused changes in Earth ecosystems and environments. Some of the most dramatic changes have occurred in the Arctic, where sea ice is on the decline. Record-breaking ice extent lows have been the new normal since 2002, according to NASA, and studies are finding that even the oldest, multiyear sea ice is thinning rapidly. Summer 2020 was one of the worst years ever for summer sea ice extent, with only one year on record – 2012 – exhibiting a lower ice extent. Scientists now expect the first ice-free Arctic summer sometime between 2040 and 2060

Glaciers are retreating globally, particularly in the middle latitudes, Mosley-Thompson said. Montana's Glacier National Park was home to 150 glaciers in 1850. Today, there are only 25. Mosley-Thompson and her team estimate that the last tropical glaciers will disappear within the next decade.

Melting ice and the expansion of ocean waters due to heat have already contributed to rising sea levels. According to NOAA, the global average sea level has risen 8 to 9 inches (21 to 24 centimeters) since 1880. The rate of rise is increasing, from 0.06 inches (1.4 millimeters) per year in the 20th century to 0.14 inches (3.6 mm) per year from 2006 to 2015. According to NOAA, this sea level rise has translated to a 300% to 900% increase in high-tide flooding in coastal areas of the United States. 

Ocean water absorbs carbon dioxide from the atmosphere, which creates a chemical reaction that causes ocean acidification. The global average pH of ocean surface waters has decreased by 0.11 since the Industrial Revolution began — a 30% increase in acidity — according to NOAA's Pacific Marine Environmental Laboratory. Increasing ocean acidity makes it more difficult for corals to build their carbonate skeletons and for shelled animals such as clams and some types of plankton to survive. 

Climate change is even affecting the timing of spring-like weather. The earliest spring (as defined by plant growth and temperatures) on record in the United States was in March 2012. Climate models now suggest that such early springs could be the norm by 2050. But late freezes will likely still occur, creating conditions in which plants could leaf out early and then be damaged by cold temperatures. Climate models also predict the exacerbation of alarming trends in droughts and wildfires due to warmer temperatures.

Models are a key tool for climate scientists, said Kathie Dello, a state climatologist for North Carolina. There is no way to compare different futures for Earth in the real world, Dello said, but models enable scientists to create virtual versions of the planet to test different scenarios. Though the Earth system is complicated, these computer models have proved capable of predicting future climate trends. A 2020 paper in the journal Geophysical Research Letters found that climate model predictions published between the 1970s and 2010 were accurate when compared with the actual warming that occurred after publication.

Can we reverse climate change?

A growing number of business leaders, government officials and private citizens are concerned about climate change and its implications, and they are proposing steps to halt and reverse the trend.

"While some argue that 'the Earth will heal itself,' the natural processes for removing this human-caused CO2 from the atmosphere work on the timescale of hundreds of thousands to millions of years," Josef Werne, a geochemist and paleoclimatologist at the University of Pittsburgh, said. "So, yes, the Earth will heal itself, but not in time for our cultural institutions to be preserved as they are. Therefore, in our own self-interests, we must act in one way or another to deal with the changes in climate we are causing."

If all human greenhouse gas emissions stopped immediately, Earth would likely still experience more warming, some studies suggest, because carbon dioxide remains in the atmosphere for hundreds of years. There are proposals that could theoretically reverse some of this "locked in" warming by removing carbon dioxide from the atmosphere, such as carbon capture and storage, which involves injecting carbon into underground reservoirs. Advocates argue that carbon capture and storage is technologically feasible, but market forces have prevented widespread adoption. 

Whether or not removing already-emitted carbon from the atmosphere is feasible, preventing future warming requires humans to stop causing the emission of greenhouse gases. The most ambitious effort to forestall warming thus far is the Paris Agreement. This nonbinding international treaty, which came into effect in November 2016, aims to keep warming "well below 2 degrees Celsius [3.6 F] above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius [2.7 F]," according to the United Nations. Each signatory to the treaty agreed to set their own voluntary emissions limits and to make them stricter over time. Climate scientists said that the emissions limits that were outlined in the agreement wouldn't keep warming as low as 1.5 or even 2 degrees C, but that it would be an improvement over the "business-as-usual" scenario in which no changes are made to cut greenhouse gas emissions.

Under the Obama administration, the United States pledged to limit greenhouse emissions to less than 28% of 2005 levels by 2025. However, President Donald Trump announced soon after his election that his administration would not honor the Paris Agreement. The Trump administration began the formal withdrawal process from the agreement in 2019. Upon assuming the presidency in 2021, Joe Biden re-committed the U.S. to the Paris Agreement. A 2021 study found that greenhouse emissions have already "locked in" enough warming such that Earth will warm more than 3.6 F, pushing past the Paris Agreement's goal. However, curbing emissions could still slow the temperature rise to a more manageable rate and reduce the ultimate peak.

Several state and local governments have launched their own efforts to combat climate change. For instance, 24 states and Puerto Rico have joined the U.S. Climate Alliance, pledging to meet goals set in the Paris Agreement regardless of politics at the federal level. 

"The federal government, even when it's operating well, is not the most nimble institution," Dello said. "But states and cities are a little more flexible."

Additional resources

For more on the sources of today's carbon's emissions, see the Live Science reference article on global warming. For a global view of how temperatures have changed over time, visit NASA's Earth Observatory. NOAA also catalogs signs of a warming world, from sea surface temperatures to shrinking Arctic sea ice to increased water vapor in the air. 

The Intergovernmental Panel on Climate Change issues regular reports on the state of climate science. The World Bank also tracks data related to climate change and lists climate mitigation projects around the globe.


Intergovernmental Panel on Climate Change. Sixth Assessment Report. Feb. 28, 2022. https://www.ipcc.ch/assessment-report/ar6/

United States Geological Survey. Climate Change Viewer. Accessed March 22, 2022. https://www.usgs.gov/tools/national-climate-change-viewer-nccv

National Snow and Ice Data Center. Arctic Sea Ice News & Analysis. Accessed March 23, 2022. https://nsidc.org/arcticseaicenews/

This article was originally written by Live Science contributor Stephanie Pappas and has since been updated.   

Stephanie Pappas
Live Science Contributor

Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz. 

  • Dr. J
    admin said:
    Climate change is real and humans are causing it.

    What is climate change, and how is it affecting Earth? : Read more
    Too bad there's NOT ONE hard science study demonstrating that 140 ppm DRY (fictitious state) atmosphere increase in CO2 is causing climate. Keep your speculation to yourself - and nevermind the exponentially more Solar Irradiance reaching the planet vs 1950
  • jason45
    no we are not causing it. the lake vostok ice cores have shown temps rising first, followed by co2. as the ocean warms, less co2 is held. tell iceland who just got hit with 5 feet of snow its warming. during the roman period it was so warm they grew grapes in england. more fake science.
  • Observer
    Science should be open to a reasoned on going discussion.

    Please can you read this post with an open mind ?

    I do not know the answers, I mosty believed the medias various stories until one day years ago I had a very short random conversation with an very kind lady who made a few comments that got me thinking what did I really know ?

    First there is a bigger picture we should all be concerned with - we are all being manipulated and allowing it to happen.

    In its simplest form its product advertising but there is much more.

    We know from history that what we think we know is a given truth is often proved with time misguided and false.

    All the big discussions today and in history focus on first capturing the debate and excluding other opinions by whatever means. Ridicule or censorship are often used

    We see this most clearly in business.

    What happens is business captures the politicians, academics, regulators and media by funding them through donations, advertising spending or regulator financing and business jobs for ex regulators, politicians and others

    Let us be honest this process is not a left or right thing, its a China, Russia, EU and USA thing.

    Its a Bush, Clinton, Obama, Xi, Putin and most others thing.

    Its pay to play and dont rock the boat

    Its the sportification of life. Its just become more so today

    You are in my team or you are dumb and my enemy.

    Its about capturing power not about finding the real answer.

    Winning at all cost

    Lets look outside politics

    Nuclear power is an example of how the debate was captured.

    Not JUST the pro or anti nuclear power


    the TYPE of nuclear power

    Thorium / Sodium based nuclear power was known about since WW2 but was blocked even though it is very safe and cheaper in the long term

    There is about 3x more thorium than uranium

    Plus core melt down basically cannot happen, toxic waste is relatively small and radio-activity does not last as long so decommissioning costs are far less

    The nuclear debate was captured and uranium nuclear power was used.

    There were many reasons but not because it was better or safer or cheaper for us - though it was sold that way and the thorium / sodium alternative was written out and not discussed.

    Basically other parties benefited and made more out of uranium and did not want the thorium alternative developed or researched

    Global Warming

    There are legitimate reasons both to question global warming or to say it is valid.

    Certainly there has been warming up to a point.

    However what does it really mean.

    We know humans are damaging the planet so lets stop doing that and benefit from that process.

    If it helps Global Warming great, and remain open to information as science is never settled

    We can all win regardless of our given prejudices whether correct or not.

    How ?

    Whatever one believes we can certainly agree we need to remove various pollutants from our environment - water, land, food and air.

    So lets address that and also how we can develop

    greener less toxic stable power sources including thorium/sodium nuclear power and
    use fossil fuels in other less polluting ways and processes before it runs out.

    Wind and solar power can be part of the solution but that power cannot be stored, can do damage in other ways and will have decommissioning costs that business will not pay for.

    We need alternatives.

    On Global Warming it has been shown that there have been much warmer times within the last 12,000 years and before so it seems less likely that human generated CO2 is a key driver.

    Livescience has featured articles showing the European Alps were probably ice free around 3,300 BC.

    No one seeks to discuss or explain this and that human based CO2 played no role

    This strongly implies other factors play a far greater role in earths warming and cooling than we currently publicly understand

    See the post below for links to the various articles and the Lorraine Lisiecki discovery of evidence showing a huge warming and cooling effect due to earths 3 different orbital cycles - temperature cycle data shown via core sediment samples around the world

    Other factors NASA sets out that water vapor has a significant green house warming effect but this is not really discussed

    CO2 makes up 0.0416% of the atmospheric volume while water vapor accounts for an average of about 2.5% of the atmospheric mass.

    H2O concentration vary significantly from the coldest portions of the atmosphere to as much as 5% in hot, humid air masses

    So as the earth warmed after the last ice age H2O vapor in the atmosphere grew significantly

    The orbital cycles of the Earth are set out in the livescience post above.

    UC Santa Barbara geologist Lorraine Lisiecki discovered a pattern that connects the regular changes of the Earth's orbital cycle to changes in the Earth's climate. The finding is reported in this week's issue of the scientific journal Nature Geoscience.

    Our axial tilt last reached its maximum value nearly 11,000 years ago, corresponding to the end of our last glacial maximum, with our next minimum approaching in a little under 10,000 years. If natural variations were dominant, we’d expect the next ~20,000 years to favor the growth of ice sheets

    If you want to see how other debates are captured look at the plastics debate - read the post below and watch the youtube documentary.

    I did not know how badly skewed things were until I watched the video and saw how the debate is manipulated in plain sight

    Remember business is doing this in everything we eat, breath, drink, wear and use.

    We know about some past manipulation issues but not about whats being hidden in plain sight now or recently

    Finally on Global Warming please keep an open mind both ways.

    Science is not a religion opinions can and do change 180 degrees over time

    That does not meaning we should pollute the planet or generate CO2 but it does mean we can focus on removing CO2 in a way that also properly removes all the toxins that are rapidly killing us and the planet

    Lastly if you want an alternative perspective please watch the videos by Nobel Prize winning Physicist Professor Ivar Giaeve

    You dont have to agree but he says he had no view on Global Warming and believed the media until he was asked to talk about it as a panel member at a Nobel Laureate Prize event and then did some research which shocked him.

    His actions and perspectives are genuine - that does not mean he is right but it certainly means lets ask for better answers.

    As he says science is not a religion.

    Let us all find a good way forward whereby in looking after others we also look after ourselves and our loved ones

    7mGSVsl-ingView: https://m.youtube.com/watch?v=7mGSVsl-ing

    TCy_UOjEir0:0View: https://m.youtube.com/watch?v=TCy_UOjEir0&t=0s
  • Broadlands
    Observer said:
    That does not meaning we should pollute the planet or generate CO2 but it does mean we can focus on removing CO2 in a way that also properly removes all the toxins that are rapidly killing us and the planet

    Observer...You just implied that CO2 is a pollutant? Focus on removing CO2...and toxins? There are billions being spent on just that. Direct air capture and storage of CO2 under pressure in widespread geological locations. The problem with that solution is it cannot possibly remove enough CO2 to affect the Earth's climate. That technology (even scaled up globally) cannot even remove and safely store just one part-per-million. Never mind those other ppms needed to lower the atmospheric burden to reach a Net-zero goal. A better way forward is to focus our resources on adaptation to whatever the climate decides to do. We will need to do that anyhow.
  • Observer
    I do not absolutely think or know CO2 is a pollutant it is consumed by plants to create growth.

    I do think that it is often linked to other toxins being released with it from power stations cars and industry or mining

    I believe we should stop polluting the planet and what we eat drink and breath while better reseasrch is done on what effects the planets climate.

    Watch Nobel Prize winning Physicist Professor Ivar Giaeve youtube videos above

    Broadlands said:
    A better way forward is to focus our resources on adaptation to whatever the climate decides to do. We will need to do that anyhow.

    Your comments make sense and part of that process is to understand the very long term cyclical nature of the planets climate - including from its 3 long term orbits, the 12 year and longer solar cycles and the ocean currents to name just 3 factors.

    We know for example the african desert was once green and but the climate changed and that Vikings settled in Greenland for around 500 years when the climate was warmer but then had to leave probably as it got too cold for farming

    Let us all move forward to a better understanding of what drives the climate and not make it a religion that cannot be questioned