Climate.gov: Are humans causing or contributing to global warming?

Yes, by increasing the abundance of greenhouse gases in the atmosphere, human activities are amplifying Earth’s natural greenhouse effect.

• Virtually all climate scientists agree that this increase in heat-trapping gases is the main reason for the 1.8°F (1.0°C) rise in global average temperature since the late nineteenth century.
• Carbon dioxide, methane, nitrous oxide, ozone, and various chlorofluorocarbons are all human-emitted heat-trapping gases.
• Among these, carbon dioxide is of greatest concern to scientists because it exerts a larger overall warming influence than the other gases combined.