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Atmospheric methane and climate change

Methane is an important greenhouse gas, responsible for around 30% of the rise in global temperatures since the industrial revolution.

Methane has a global warming potential (GWP) of 29.8 ± 11 compared to CO (potential of 1) over a 100-year period, and 82.5 ± 25.8 over a 20-year period. This means that, for example, a leak of one tonne of methane is equivalent to emitting 82.5 tonnes of carbon dioxide. Burning methane and producing carbon dioxide also reduces the greenhouse gas impact compared to simply venting methane to the atmosphere.

As methane is gradually converted into carbon dioxide (and water) in the atmosphere, these values include the climate forcing from the carbon dioxide produced from methane over these timescales.

Annual global methane emissions are currently approximately 580 Mt, 40% of which is from natural sources and the remaining 60% originating from human activity, known as anthropogenic emissions. The largest anthropogenic source is agriculture, responsible for around one quarter of emissions, closely followed by the energy sector, which includes emissions from coal, oil, natural gas and biofuels.

Historic methane concentrations in the world's atmosphere have ranged between 300 and 400 nmol/mol during glacial periods commonly known as ice ages, and between 600 and 700 nmol/mol during the warm interglacial periods. A 2012 NASA website said the oceans were a potential important source of Arctic methane, but more recent studies associate increasing methane levels as caused by human activity.

Global monitoring of atmospheric methane concentrations began in the 1980s. The Earth's atmospheric methane concentration has increased 160% since preindustrial levels in the mid-18th century. In 2013, atmospheric methane accounted for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases. Between 2011 and 2019 the annual average increase of methane in the atmosphere was 1866 ppb. From 2015 to 2019 sharp rises in levels of atmospheric methane were recorded.

In 2019, the atmospheric methane concentration was higher than at any time in the last 800,000 years. As stated in the AR6 of the IPCC, "Since 1750, increases in CO (47%) and CH (156%) concentrations far exceed, and increases in N O (23%) are similar to, the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years (very high confidence)".

In February 2020, it was reported that fugitive emissions and gas venting from the fossil fuel industry may have been significantly underestimated. The largest annual increase occurred in 2021 with the overwhelming percentage caused by human activity.

Climate change can increase atmospheric methane levels by increasing methane production in natural ecosystems, forming a climate change feedback. Another explanation for the rise in methane emissions could be a slowdown of the chemical reaction that removes methane from the atmosphere.

Over 100 countries have signed the Global Methane Pledge, launched in 2021, promising to cut their methane emissions by 30% by 2030. This could avoid 0.2˚C of warming globally by 2050, although there have been calls for higher commitments in order to reach this target. The International Energy Agency 's 2022 report states "the most cost-effective opportunities for methane abatement are in the energy sector, especially in oil and gas operations".