What is the primary greenhouse gas released from the burning of fossil fuels?

The primary greenhouse gas released from the burning of fossil fuels is carbon dioxide. Coal, oil, and natural gas contain carbon that was stored underground for millions of years. When these fuels burn, their carbon combines with oxygen, producing carbon dioxide (CO₂), which accumulates in the atmosphere and traps outgoing heat.

Fossil-fuel combustion occurs in power plants, vehicles, factories, aircraft, and buildings. Carbon dioxide is also released when forests or other carbon-rich materials burn, but fossil fuels are a major human source because they transfer long-buried carbon into the active carbon cycle.

Carbon dioxide is not the most powerful greenhouse gas molecule by molecule, but it is emitted in such large quantities and remains influential for a long time. Methane and nitrous oxide also matter, yet they are not the primary gas produced by burning fossil fuels. A common mix-up is confusing the main greenhouse gas with the most abundant human-caused emission by mass: the answer to this question is CO₂.