Global warming is real, and it is changing the climate.

Collectively, the weight of human beings and their activities are changing the face of Earth. The lights of cities can be seen from orbit; large areas that were once forests, wetlands, and grasslands have been transformed into agricultural land; and the gases produced by vehicles and other machines are slowly altering the planet’s atmosphere, by adding chemicals that strengthen the atmosphere’s ability to trap heat energy. By the end of the 20th century, greenhouse gas emissions from human activities had become so great that they had begun to influence temperature and precipitation patterns, and scientists and other experts began to worry how these changes would affect natural ecosystems, the reliability of crop production, and our future way of life.

A vigorous debate continues over the extent and seriousness of rising surface temperatures, the effects of past and future warming on human life, and the need for action to reduce future warming and deal with its consequences. Discussions and deliberations aside, there is significant evidence that climates around the world are changing, and we humans are playing important roles in these changes. This section provides an overview of the scientific background and public policy debate related to global warming.

Between 1970 and 2019, atmospheric carbon concentrations have risen by more than 86 parts per million (ppm) to ~412 ppm.

The Keeling Curve, April 5, 2019. Scripps Institution of Oceanography, UC San Diego.

Know the Problems

No environmental problem in recent years has received more attention than that of global warming. Evidence continues to mount showing that carbon dioxide and other greenhouse gases produced largely by human activities are building up in our atmosphere and influencing temperature and precipitation patterns around the world. Although climate change has continued throughout Earth’s history, during this current phase, human beings and their activities are playing an ever-increasing role in the process. Read more about global warming and its influence on climate.

Global Warming Q&A

The Earth Is Heating Up


14 °C

The global mean air temperature between 1951 and 1980
was 14 °C (57 °F).

Since 1901

0.7–0.9 °C

The average rate of change of
global average surface temperature
per century

Since 1975

1.5–1.8 °C

The average rate of change of
global average surface temperature
has nearly doubled.

Source. NASA Earth Observatory and State of the Climate in 2017. Special Supplement to the Bulletin of the American Meteorological Society Vol. 99, No. 8, August 2018.

Know the Causes

The main causes of global warming revolve around the combustion of fossil fuels. Oil, coal, and other fossil fuels are burned to power our vehicles and produce electricity for our homes and industries. Although human beings have found other ways to generate power, fossil-fuel combustion, generally speaking, has been a relatively cheap and easy way to do it thus far. Learn more about the fuels, movements, and activities that have contributed to global warming.

Know the Solutions

Global warming is a solvable environmental problem, because solutions rest with how human beings will produce electricity and other forms of power in the future. Renewable energy sources such as wind, solar, and nuclear power have become increasingly reliable, and they do not give off carbon dioxide and other greenhouse gases. If enough people, governments, and places of business around the world choose renewables over fossil fuels, the worst effects of global warming can be avoided. Learn more about the different forms of renewable energy and other solutions to the problem of global warming.

Take Action Against Global Warming

There is no planet B.

Do your part to change our course in history. Learn more about how you can work to solve Earth’s environmental challenges in your home and in your community.