Climate change refers to changes in Earth’s long-term average temperature resulting from human activities. These include burning fossil fuels, deforestation, wetland loss, and other human-caused greenhouse gas emissions. Other factors, such as natural variations in solar radiation and some weather phenomena, also affect the climate system.
Earth has warmed since the 1950s because of these human activities. Greenhouse gases—carbon dioxide, methane, nitrous oxide, and several human-made gases containing fluorine and chlorine—increase the amount of heat trapped in Earth’s atmosphere, much like glass in a greenhouse keeps plants warm. The greenhouse effect is occurring at a rate unprecedented in recorded history.
Human-caused warming is already harming people and ecosystems worldwide. Rising temperatures will increase deaths and illnesses from hot days and reduce deaths from cold ones, and lower crop yields. It will worsen droughts and water shortages, increase insect outbreaks, cause wildfires to grow larger and more severe, and intensify flooding.
Climate change also raises energy costs and may slow economic growth, especially in poorer countries that have less ability to adapt. Investments to adapt to climate change may boost GDP in the year they are made, but they may crowd out investments that would have been more productive in the absence of climate change. Losses to productive capital will decrease the amount of money available for new investments, which will slow economic growth over time. Moreover, investments to replace lost or damaged capital will be offset by lower productivity in buildings and equipment that are more costly to operate in warmer or wetter conditions.