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Greenhouse gases (GHGs) are atmospheric constituents that absorb infrared radiation and trap heat, reinforcing the natural greenhouse effect and contributing to climate change. The major anthropogenic GHGs are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases, including HFCs, PFCs, and SF6. Water vapor is the most abundant greenhouse gas, but its concentration is largely controlled by temperature and climate feedbacks rather than direct emissions, so it is treated differently in many inventories.

Human activities increase GHG concentrations by burning fossil fuels (coal, oil, gas) for energy and transport; industrial processes; deforestation and other land-use changes; agricultural practices; and waste management. Natural sources and sinks also influence levels, but the current atmospheric growth is driven predominantly by human activities.

Emissions are typically reported in terms of CO2 equivalents (CO2e), using a metric such as Global Warming Potential (GWP) to compare the climate impact of different gases over a chosen time horizon (commonly 100 years). Atmospheric lifetimes vary: CO2 can persist for centuries, methane about a decade to a few decades, nitrous oxide about a century, and fluorinated gases for varying timescales from years to millennia.

International frameworks, including the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, address GHG reporting and reductions. Mitigation strategies focus on decarbonizing energy supply, improving energy efficiency, expanding renewable energy, deploying methane capture and reuse, changing agricultural practices, protecting and expanding forests, and implementing carbon pricing and refrigerant management.