Climate change is the long-term, widespread and dangerous increase in Earth’s average temperature caused by human activities such as burning fossil fuels, unequal energy use, land-use changes, and pollution. Over a century of these activities has produced a large imbalance of energy in Earth’s atmosphere, trapping heat and warming the planet. The resulting temperature changes are already visible in the melting of global ice sheets, rising sea level, more frequent and intense heatwaves, and changing weather patterns.
The Sun supplies Earth with solar energy, some of which is reflected back into space and the rest absorbed by the surface and atmosphere. The atmosphere then re-radiates some of the energy back into space, some of it as heat (longwave or infrared radiation). The balance between incoming and outgoing energy is what drives the climate system. Small disturbances in this balance can have a big impact on the climate system.
Human activities are the biggest source of greenhouse gases, particularly carbon dioxide, that contribute to climate change. Among the most important sources of CO2 emissions are road vehicles, airplanes, ships and trains, and coal plants. Most of these vehicles run on fossil fuels such as petroleum, natural gas, and oil.
In the United States, communities with the fewest resources will experience climate change impacts first and hardest. They will be less able to protect themselves from food insecurity, water shortages, or extreme weather and will have a harder time recovering from climate-related disasters like hurricanes and wildfires. Some communities will be displaced because of sea level rise and other changes such as declining crop yields and heat-related health problems.