Global warming is a gradual increase in Earth’s surface temperatures caused by humans and their activities. It’s a result of the greenhouse effect, in which certain gases in the atmosphere trap heat and slow its release back into space. The major greenhouse gases include carbon dioxide, methane, nitrous oxide and chlorofluorocarbons. The concentrations of these gases have increased over the last century. This warming has affected many of Earth’s ecosystems, and the changes are expected to worsen unless we reduce our emissions.
Scientists have tracked global surface temperatures since 1850, when accurate records began. They use a variety of methods and evidence to study climate changes, including thermometers, satellite data and ocean observations. They also look at “paleoclimatic” data from natural sources such as tree rings, pollen grains and ice cores.
Although the Sun plays a role in climate change, scientists have determined that human activity is responsible for the current warming trend. The most common reason for this is the increasing levels of greenhouse gases in the atmosphere, especially carbon dioxide. Humans produce greenhouse gases through a variety of activities, but the main sources are burning fossil fuels (oil, gas and coal) and land clearing.
Climate change is happening faster than most living things can adapt. For example, changes in the length of the growing season are affecting the seasonal activities of plants and animals. In addition, the loss of Arctic sea ice is affecting marine species that depend on it for food and shelter, such as polar bears and walrus. The ongoing rise in global surface temperatures is also causing sea level to rise and bringing more severe weather events.