Methane emissions

Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% of methane released globally was from human activities, while natural sources contributed about 40%. Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits.
Since the Industrial Revolution, concentrations of methane in the atmosphere have more than doubled, and about 20 percent of the warming the planet has experienced can be attributed to the gas. About one-third of anthropogenic emissions are from gas release during the extraction and delivery of fossil fuels; mostly due to gas venting and gas leaks from both active fossil fuel infrastructure and orphan wells. Russia is the world's top methane emitter from oil and gas. The International Energy Agency highlights that abandoned coal mines and oil and gas wells have become significant sources of methane emissions. If considered a country, these emissions would rank as the fourth-largest globally, surpassing those of Iran. The IEA estimates that addressing over 8 million abandoned onshore oil and gas sites would cost about $100 billion.
Animal agriculture is a similarly large source, primarily because of enteric fermentation by ruminant livestock such as cattle and sheep. According to the Global Methane Assessment published in 2021, methane emissions from livestock are the largest sources of agricultural emissions worldwide A single cow can make up to 99 kg of methane gas per year. Ruminant livestock can produce 250 to 500 L of methane per day.
Human consumer waste flows, especially those passing through landfills and wastewater treatment, have grown to become a third major category. Plant agriculture, including both food and biomass production, constitutes a fourth group, with rice production being the largest single contributor.
The world's wetlands contribute about three-quarters of the enduring natural sources of methane. Seepages from near-surface hydrocarbon and clathrate hydrate deposits, volcanic releases, wildfires, and termite emissions account for much of the remainder. Contributions from the surviving wild populations of ruminant mammals are vastly overwhelmed by those of cattle, humans, and other livestock animals.
The Economist recommended setting methane emissions targets as a reduction in methane emissions would allow for more time to tackle the more challenging carbon emissions".

Atmospheric concentration and warming influence

The atmospheric methane concentration is increasing and exceeded 1860 parts per billion in 2019, equal to two-and-a-half times the pre-industrial level. The methane itself causes direct radiative forcing that is second only to that of carbon dioxide. Due to interactions with oxygen compounds stimulated by sunlight, CH₄ can also increase the atmospheric presence of shorter-lived ozone and water vapour, themselves potent warming gases: atmospheric researchers call this amplification of methane's near-term warming influence indirect radiative forcing. When such interactions occur, longer-lived and less-potent CO₂ is also produced. Including both the direct and indirect forcings, the increase in atmospheric methane is responsible for about one-third of near-term global heating.
Though methane causes far more heat to be trapped than the same mass of carbon dioxide, less than half of the emitted CH₄ remains in the atmosphere after a decade. On average, carbon dioxide warms for much longer, assuming no change in rates of carbon sequestration. The global warming potential is a way of comparing the warming due to other gases to that from carbon dioxide, over a given time period. Methane's GWP₂₀ of 85 means that a ton of CH₄ emitted into the atmosphere creates approximately 85 times the atmospheric warming as a ton of CO₂ over a period of 20 years. On a 100-year timescale, methane's GWP₁₀₀ is in the range of 28–34.
Methane emissions are important as reducing them can buy time to tackle carbon emissions.

Overview of emission sources

Biogenic methane is actively produced by microorganisms in a process called methanogenesis. Under certain conditions, the process mix responsible for a sample of methane may be deduced from the ratio of the isotopes of carbon, and through analysis methods similar to carbon dating.

Anthropogenic

, emission volumes from some sources remain more uncertain than others; due in part to localized emission spikes not captured by the limited global measurement capability. The time required for a methane emission to become well-mixed throughout earth's troposphere is about 1–2 years.
Satellite data indicate over 80% of the growth of methane emissions during 2010–2019 are tropical terrestrial emissions.
There is accumulating research and data showing that oil and gas industry methane emissions – or from fossil fuel extraction, distribution and use – are much larger than thought.

Natural

Natural sources have always been a part of the methane cycle. Wetland emissions have been declining due to draining for agricultural and building areas.

Methanogenesis

Most ecological emissions of methane relate directly to methanogens generating methane in warm, moist soils as well as in the digestive tracts of certain animals. Methanogens are methane producing microorganisms. In order to produce energy, they use an anaerobic process called methanogenesis. This process is used in lieu of aerobic, or with oxygen, processes because methanogens are unable to metabolise in the presence of even small concentrations of oxygen. When acetate is broken down in methanogenesis, the result is the release of methane into the surrounding environment.
Methanogenesis, the scientific term for methane production, occurs primarily in anaerobic conditions because of the lack of availability of other oxidants. In these conditions, microscopic organisms called archaea use acetate and hydrogen to break down essential resources in a process called fermentation.
Acetoclastic methanogenesis – certain archaea cleave acetate produced during anaerobic fermentation to yield methane and carbon dioxide.
Hydrogenotrophic methanogenesis – archaea oxidize hydrogen with carbon dioxide to yield methane and water.
While acetoclastic methanogenesis and hydrogenotrophic methanogenesis are the two major source reactions for atmospheric methane, other minor biological methane source reactions also occur. For example, it has been discovered that leaf surface wax exposed to UV radiation in the presence of oxygen is an aerobic source of methane.

Natural methane cycles

Its concentration is higher in the Northern Hemisphere since most sources are located on land and the Northern Hemisphere has more land mass. The concentrations vary seasonally, with, for example, a minimum in the northern tropics during April−May mainly due to removal by the hydroxyl radical.
For example, plants that produce methane can emit as much as two to four times more methane during the day than during the night. This is directly related to the fact that plants tend to rely on solar energy to enact chemical processes.

Wetlands

In wetlands, where the rate of methane production is high, plants help methane travel into the atmosphere—acting like inverted lightning rods as they direct the gas up through the soil and into the air. They are also suspected to produce methane themselves, but because the plants would have to use aerobic conditions to produce methane, the process itself is still unidentified, according to a 2014 Biogeochemistry article.
A 1994 article on methane emissions from northern wetlands said that since the 1800s, atmospheric methane concentrations increased annually at a rate of about 0.9%.

Human-caused methane emissions

The AR6 of the IPCC said, "It is unequivocal that the increases in atmospheric carbon dioxide, methane, and nitrous oxide since the pre-industrial period are overwhelmingly caused by human activities." Atmospheric methane accounted for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases.
According to the 2021 assessment by the Climate and Clean Air Coalition and the United Nations Environment Programme over 50% of global methane emissions are caused by human activities in fossil fuels, waste, and agriculture. The oil and gas industry accounts for 23%, and coal mining for 12%. Twenty percent of global anthropogenic emissions stem from landfills and wastewater. Manure and enteric fermentation represent 32%, and rice cultivation represents 8%.
The most clearly identified rise in atmospheric methane as a result of human activity occurred in the 1700s during the industrial revolution. During the 20th centurymainly because of the use of fossil fuelsconcentration of methane in the atmosphere increased, then stabilized briefly in the 1990s, only to begin to increase again in 2007. After 2014, the increase accelerated and by 2017, reached 1,850 parts per billion.
Increases in methane levels due to modern human activities arise from a number of specific sources including industrial activity; from extraction of oil and natural gas from underground reserves; transportation via pipeline of oil and natural gas; and thawing permafrost in Arctic regions, due to global warming which is caused by human use of fossil fuels.
The primary component of natural gas is methane, which is emitted to the atmosphere in every stage of natural gas "production, processing, storage, transmission, and distribution".

Emissions due to oil and gas extraction

A 2005 Wuppertal Institute for Climate, Environment and Energy article identified pipelines that transport natural gas as a source of methane emissions. The article cited the example of Trans-Siberian natural gas pipeline system to western and Central Europe from the Yamburg and Urengoy exist gas fields in Russia with a methane concentration of 97%. In accordance with the IPCC and other natural gas emissions control groups, measurements had to be taken throughout the pipeline to measure methane emissions from technological discharges and leaks at the pipeline fittings and vents. Although the majority of the natural gas leaks were carbon dioxide, a significant amount of methane was also being consistently released from the pipeline as a result of leaks and breakdowns. In 2001, natural gas emissions from the pipeline and natural gas transportation system accounted for 1% of the natural gas produced. Between 2001 and 2005, this was reduced to 0.7%, the 2001 value was significantly less than that of 1996.
A 2012 Climatic Change article and 2014 publication by a team of scientists led by Robert W. Howarth said that there was strong evidence that "shale gas has a larger GHG footprint than conventional gas, considered over any time scale. The GHG footprint of shale gas also exceeds that of oil or coal when considered at decadal time scales." Howarth called for policy changes to regulate methane emissions resulting from hydraulic fracturing and shale gas development.
A 2013 study by a team of researchers led by Scot M. Miller, said that U.S. greenhouse gas reduction policies in 2013 were based on what appeared to be significant underestimates of anthropogenic methane emissions. The article said, that "greenhouse gas emissions from agriculture and fossil fuel extraction and processing"oil and/or natural gaswere "likely a factor of two or greater than cited in existing studies." By 2001, following a detailed study anthropogenic sources on climate change, IPCC researchers found that there was "stronger evidence that most of the observed warming observed over the last 50 years attributable to human activities." Since the Industrial Revolution humans have had a major impact on concentrations of atmospheric methane, increasing atmospheric concentrations roughly 250%. According to the 2021 IPCC report, 30–50% of the current rise in temperatures is caused by emissions of methane, and reducing methane is a fast way of climate change mitigation. An alliance of 107 countries, including Brazil, the EU and the U.S., have joined the pact known as the Global Methane Pledge, committing to a collective goal of reducing global methane emissions by at least 30% from 2020 levels by 2030.
The European Union adopted methane regulations in 2024. The law requires oil and gas developers to monitor, measure, and report methane emissions. Producers must stop flaring unused natural gas and use satellite imagery to detect leaks.