"Global warming" redirects here. For other uses, see Climate change

Greenhouse gases
Main articles: Greenhouse gas, Greenhouse gas emissions, Greenhouse effect, and Carbon dioxide in Earth's atmosphere
CO₂ concentrations over the last 800,000 years as measured from ice cores^{[69][70][71][72]} (blue/green) and directly^[73] (black)
Greenhouse gases are transparent to sunlight, and thus allow it to pass through the atmosphere to heat the Earth's surface. The Earth radiates it as heat, and greenhouse gases absorb a portion of it. This absorption slows the rate at which heat escapes into space, trapping heat near the Earth's surface and warming it over time.^[74] Before the Industrial Revolution, naturally-occurring amounts of greenhouse gases caused the air near the surface to be about 33 °C warmer than it would have been in their absence.^[75][76] While water vapour (≈50%) and clouds (≈25%) are the biggest contributors to the greenhouse effect, they increase as a function of temperature and are therefore feedbacks. On the other hand, concentrations of gases such as CO₂ (≈20%), tropospheric ozone,^[77] CFCs and nitrous oxide are not temperature-dependent, and are therefore external forcings.^[78]
Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas),^[79] has increased the amount of greenhouse gases in the atmosphere, resulting in a radiative imbalance. In 2019, the concentrations of CO₂ and methane had increased by about 48% and 160%, respectively, since 1750.^[80] These CO₂ levels are higher than they have been at any time during the last 2 million years. Concentrations of methane are far higher than they were over the last 800,000 years.^[81]
The Global Carbon Project shows how additions to CO₂ since 1880 have been caused by different sources ramping up one after another.
Global anthropogenic greenhouse gas emissions in 2019 were equivalent to 59 billion tonnes of CO₂. Of these emissions, 75% was CO₂, 18% was methane, 4% was nitrous oxide, and 2% was fluorinated gases.^[82] CO₂ emissions primarily come from burning fossil fuels to provide energy for transport, manufacturing, heating, and electricity.^[4] Additional CO₂ emissions come from deforestation and industrial processes, which include the CO₂ released by the chemical reactions for making cement, steel, aluminum, and fertiliser.^[83] Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction.^[84] Nitrous oxide emissions largely come from the microbial decomposition of fertiliser.^[85]
Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant carbon sink for CO₂. Land-surface sink processes, such as carbon fixation in the soil and photosynthesis, remove about 29% of annual global CO₂ emissions.^[86] The ocean also serves as a significant carbon sink via a two-step process. First, CO₂ dissolves in the surface water. Afterwards, the ocean's overturning circulation distributes it deep into the ocean's interior, where it accumulates over time as part of the carbon cycle. Over the last two decades, the world's oceans have absorbed 20 to 30% of emitted CO₂.^[87]