Main sources of emissionsThe primary GHG emitted through human activities is CO2, which accounts for roughly 75 percent of GHG emissions. In 2020, global CO2 emissions totaled 35 Gt – a reduction of five percent compared with the previous year due to the impacts of COVID-19. The power industry accounted for 37 percent of CO2 emissions that year, making it the single largest source of CO2 emissions. The main reason for this is that most of the world’s power production comes from coal - the most carbon-intensive fossil fuel. Despite a COVID-19-related reduction, global coal emissions were still 14 GtCO2 in 2020. The second-largest source of CO2 is the transportation sector, which was responsible for 20 percent of emissions in 2020. Of this share, 41 percent came from passenger car emissions.
While the burning of fossil fuels is the primary source of CO2, land use activities such as deforestation and clearing land for agricultural purposes also releases large amounts of CO2 into the atmosphere.