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A list of the top 10 global regions where natural or anthropogenic sources emit methane on a continuous, "persistent" basis was recently in Atmospheric Chemistry and Â鶹ÒùÔºics.

The study analyzed data and measured emissions from hundreds of potential sources of methane based on satellite data.

Data from the Copernicus Sentinel-5P mission was used to study and estimate methane emissions at 217 potential locations, as shown on the map above.

The paper focused on sources that emit methane gradually over time, in contrast to "super-emitters"—typically oil and gas operations, coal mines or poorly managed landfills—which release disproportionately large amounts of methane but not on a continuous basis.

Measuring the problem

Sentinel-5P, the result of a close collaboration between ESA, the European Commission, the Netherlands Space Office and industry, carries the state-of-the-art Tropomi instrument, which is used to map trace gases including methane.

The study is based on a new methane concentration dataset and an algorithm developed by the University of Bremen as part of the ESA Climate Change Initiative Greenhouse Gas Project, as well as the ESA Earth System Science Hub projects, Methane CAMP and SMART-CH4.

According to Claus Zehner, ESA's Mission Manager for Sentinel-5P, "Sentinel-5P is currently the only satellite that provides the feasibility to detect methane sources on a global scale and on a daily basis."

Researchers analyzed concentrations of methane (parts per billion) for 2018–2021. A location was classified as a potential persistent emitter if levels of methane were consistently higher than the surrounding area.

One of the paper's authors, Michael Buchwitz, Senior Scientist at the University of Bremen, explained, "The aim was not to identify specific events, where methane is only released for a short period of time. Instead, the aim was to identify sources that emit almost continuously during the four years that were analyzed. This includes natural sources such as wetlands, but also coal mining areas or large oil and gas fields."

Natural emitters

Wetlands are the most important natural sources of methane as microbes found in wetland soil emit high levels of the gas. The two natural sources indicated in the study's top 10 are both wetlands: the Sudd wetlands in southern Sudan and the Iberá wetlands in Argentina.

The Sudd wetlands are a well-known methane source. Increased methane concentrations were detected across the Sudd region in 2020 and have been attributed to heavier rainfall and increased water flow from the White Nile. The region spans 500 km north to south and 200 km east to west, covering some 57,000 sq km, although it can double in size during rainy season.

The Iberá wetlands, in the Corrientes province of Argentina, is about half the size of Sudd and is an important freshwater source in South America. It is listed as the third biggest potential persistent methane source in the study.

Anthropogenic sources

The study also identified potential persistent methane emissions related to human activity. The biggest anthropogenic source was from the oil and gas fields on the west coast of Turkmenistan.

Several oil and gas persistent emission sites were identified in North America, including the Permian Basin, which is America's highest producing oil field, spanning the border between Texas and New Mexico.

The top 10 persistent emitting sources included three coal fields in Shanxi province in China, as well as Kuznetsk, one of the largest coal mining areas in Russia.

The study also looked at other anthropogenic sources, which include landfills, wastewater, digestive gas from ruminant animals such as cattle, sheep and goats, as well as manure, rice and energy buildings.

Why is methane important?

Methane is the second most important greenhouse gas after carbon dioxide and is naturally present in the air we breathe. But its increasing concentration in the atmosphere is an important factor in global warming.

Until 1850, levels were recorded at between 680 and 790 parts per billion, or ppb, according to data from NOAA Global Monitoring Laboratory. In the past decade, methane levels in Earth's atmosphere have reached almost three times the levels in 1850 to more than 1900 ppb. High-emitting and persistent methane sources make up a large share of global methane emissions and the Global Methane Budget 2024 shows there has been a significant rise in anthropogenic methane emissions in the past two decades.

Methane has a more powerful warming effect than carbon dioxide, although it has a much shorter duration in the atmosphere before it decomposes. Over a 20-year timescale, each kilogram of methane emitted has a global warming potential more than 80 times more potent than carbon dioxide. Reducing methane emissions is therefore an important strategy for tackling the causes of global warming.