CO2 emissions are the release of carbon dioxide gas into the atmosphere. They are a major contributor to climate change, as the gas traps heat in the atmosphere and contributes to the greenhouse effect. CO2 emissions come from a variety of sources, including the burning of fossil fuels (such as coal, oil, and natural gas) for energy, industrial processes, transportation, and deforestation. A reduction in emissions is widely recognized as the best way to avoid climate change’s worst impacts.