GHGs

Greenhouse gases (GHGs) are gases in Earth’s atmosphere that absorb infrared radiation and trap heat, contributing to the greenhouse effect that keeps the planet warmer than it would be otherwise. They originate from natural processes and human activities, and their concentrations have risen markedly since the industrial era, increasing the warming influence of the atmosphere.

The major GHGs include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), tropospheric ozone (O3), and a group of fluorinated gases such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). Water vapor is also a greenhouse gas, but its concentration is controlled largely by temperature and feedbacks rather than direct emissions.

Each gas has a different atmospheric lifetime and radiative efficiency. CO2 persists for centuries to millennia and is the largest contributor to long‑term anthropogenic forcing. CH4 is far more effective at absorbing heat per molecule than CO2 but remains in the atmosphere for about a decade. N2O lasts about a century and is influenced by soil, manure, and industrial processes. The fluorinated gases have a wide range of lifetimes, from several years to thousands of years, and collectively can produce strong warming per molecule.

Measurement and reporting of GHGs are conducted through global monitoring networks and inventories that express emissions in CO2‑equivalent terms using metrics like the Global Warming Potential. International agreements, including the Kyoto Protocol and the Paris Agreement, aim to reduce anthropogenic GHG emissions through decarbonization, efficiency gains, methane mitigation, and carbon capture and removal initiatives.