Which gas is the main human-caused greenhouse gas by emissions?

Carbon dioxide is the main human-caused greenhouse gas by emissions.

Carbon dioxide absorbs infrared radiation emitted by Earth’s surface, helping retain heat in the lower atmosphere. Human activities, especially burning coal, oil, and natural gas, cement production, and land-use change, add carbon dioxide to the atmosphere faster than natural systems can remove it.

Water vapor is the most abundant greenhouse gas in the atmosphere, but it mainly acts as a feedback rather than the initial long-lived forcing from human activity. Methane and nitrous oxide are also important greenhouse gases. Carbon dioxide is especially significant because it persists in the climate system and is emitted in very large quantities.