A greenhouse gas (GHG) is a gas that traps heat in the atmosphere. The primary greenhouse gases in Earth's atmosphere are water vapour (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). Human activities are the primary driver of the increase of carbon dioxide and methane in the atmosphere.
Anthropogenic activities have increased the atmospheric concentration of carbon dioxide by almost 50% since the 1750s. In 2021 the average concentration stood at 419 parts per million (or 0.419 grams per litre of air), an increase from 280 parts per million in the 1750s.
The vast majority of human emitted carbon dioxide comes from the combustion of fossil fuels like coal, oil and natural gas. Cement manufacturing, fertiliser production and deforestation also play a significant role.