Climate Change: Causes, Evidence, and Effects

Learn the causes, evidence, and effects of climate change, including how human activities are driving global warming.

What is the difference between global warming and climate change?

Global warming generally refers to the long-term increase in global average temperature as a result of human activity. Climate change is a broader term that covers changes in multiple parts of the climate system, including temperature, precipitation, and wind patterns. Global warming is one type of climate change, but not all climate change is global warming.

How do scientists know Earth is warming?

Scientists know Earth is warming because temperature records from thousands of weather stations worldwide, along with independent lines of evidence, all show the same trend. Earth's average surface temperature has risen by about 1.8 degrees Fahrenheit since 1880, with the rate of warming more than doubling since 1981. Additional evidence includes melting glaciers, rising sea levels, earlier plant blooming, and changing animal migration patterns.

Are humans causing climate change?

Yes, human activities are the main cause of recent global warming. The burning of fossil fuels adds about 9.5 billion metric tons of carbon to the atmosphere each year, while deforestation and other land cover changes add another 1.5 billion metric tons. The rapid increase in atmospheric carbon dioxide and its isotopic fingerprint point to fossil fuels, not natural sources like volcanoes or forest fires.

How much carbon dioxide is in the atmosphere today?

Carbon dioxide in the atmosphere increased from about 280 parts per million in 1800 to 410 parts per million in 2019. Since 1750, humans have increased the abundance of carbon dioxide in the atmosphere by nearly 50 percent. A net 5 billion metric tons of human-produced carbon remain in the atmosphere each year, raising global average carbon dioxide concentrations by about 2.3 parts per million annually.

What are the effects of climate change?

Climate change is causing extreme heat, protracted drought, increased flooding, more intense storms, and rising sea levels. It is also altering natural cycles, such as causing birds to migrate earlier and plants to bloom earlier in the spring. The impacts are not distributed equally, as people of color and economically disadvantaged communities bear a much larger burden.

How much could Earth warm by the end of this century?

With significant reductions in greenhouse gas emissions, global temperature rise this century could be limited to 3.6 degrees Fahrenheit or less. Without major reductions, the increase in annual average global temperatures relative to pre-industrial times could reach 9 degrees Fahrenheit or more by the end of this century. Experts say keeping warming below 2.7 degrees Fahrenheit compared to pre-industrial temperatures would lower the risk of serious negative impacts.

Is there scientific consensus on climate change?

Yes, virtually all climate scientists agree that the increase in heat-trapping gases is the main reason for the rise in global average temperature since the late nineteenth century. Leading U.S. science agencies and organizations, including NASA, the National Academies of Sciences, Engineering, and Medicine, the American Meteorological Society, and the American Geophysical Union, have recognized global warming as a problem that threatens human and natural systems.

What is the greenhouse effect?

The greenhouse effect is the way certain atmospheric gases trap heat near Earth's surface, making the planet warm enough to support life. Human activity, especially the unchecked burning of fossil fuels over the past 150 years, has drastically increased the presence of greenhouse gases, most notably carbon dioxide. This has amplified Earth's natural greenhouse effect and pushed global temperatures to levels higher than at any other point in human history.

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