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


Climate change is real and humans are causing it.

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.”


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.


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.

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