Atmospheric methane

Atmospheric methane is the methane present in Earth's atmosphere. The concentration of atmospheric methane is increasing due to methane emissions, and is causing climate change. Methane is one of the most potent greenhouse gases.^: 82 Methane's radiative forcing (RF) of climate is direct,^: 2 and it is the second largest contributor to human-caused climate forcing in the historical period.^: 2 Methane is a major source of water vapour in the stratosphere through oxidation; and water vapour adds about 15% to methane's radiative forcing effect. The global warming potential (GWP) for methane is about 84 in terms of its impact over a 20-year timeframe. That means it traps 84 times more heat per mass unit than carbon dioxide (CO₂) and 105 times the effect when accounting for aerosol interactions.

Since the beginning of the Industrial Revolution (around 1750) the atmospheric methane concentration has increased by about 160%, with the increase being overwhelmingly caused by human activity. Since 1750 methane has contributed 3% of GHG emissions in terms of mass but is responsible for approximately 23% of radiative or climate forcing. In 2019, global methane concentrations rose from 722 parts per billion (ppb) in pre-industrial times to 1866 ppb. This is an increase by a factor of 2.6 and the highest value in at least 800,000 years.^: 4

Methane increases the amount of ozone O₃ in the troposphere (4 miles (6.4 km) to 12 miles (19 km) from the Earth's surface) and also in the stratosphere (from the troposphere to 31 miles (50 km) above the Earth's surface). Both water vapour and ozone are GHGs, which in turn adds to climate warming.^: 2