Global warming is a term for the long-term increase in average Earth surface temperatures caused by human activities. This warming is mainly due to the release of greenhouse gases such as carbon dioxide, methane, and nitrous oxide into the atmosphere. While Earth has experienced gradual warming and cooling episodes throughout its history, scientists have determined that the current increase in temperatures is unlike any other naturally triggered phenomenon and is largely caused by human activity.

When carbon dioxide and other greenhouse gases accumulate in the atmosphere, they absorb and trap heat from the Sun. As a result, Earth’s temperature rises. In addition, a warmer planet holds more water vapor, which amplifies the effects of greenhouse gases by adding extra heat to the climate system.

Warmer temperatures also reduce snow and ice in polar regions, which can disrupt the flow of the jet stream. This, in turn, can produce more extreme weather events such as hurricanes and flash floods. A warmer planet also increases rainfall, as the air can hold more moisture; this can lead to flooding and severe droughts.

Scientists use a variety of methods to study climate change, including thermometer records and other instruments. For periods before accurate thermometers were available, scientists can reconstruct temperatures from “proxies” in nature such as tree rings and ice cores. These records show that, since 1850, Earth’s surface temperature has risen on average by about 0.07 degrees Celsius or (0.13 degrees Fahrenheit) per decade. The rate of increase has increased since 1980, with recent decades being warmer than any previous decade on record.