(Bloomberg) -- A satellite detected clouds of the super-potent greenhouse gas methane coming from China’s main coal-producing region, drawing attention to a lesser-known global warming consequence of the country’s reliance on the dirtiest fossil fuel. 

The emissions likely came from multiple mines in China’s northeastern Shanxi province, which produces more than 10% of the world’s coal. One plume spotted on Dec. 21 had an estimated emissions rate of 68 metric tons of methane an hour, while another seen on Dec. 4 probably had a rate of 53 tons an hour, according to geoanalytics firm Kayrros SAS.

If both releases lasted an hour, together they would have had the same short-term climate warming impact as the annual emissions from about 6,000 U.K. cars. They were the second and third worst cases of methane pollution identified by satellite in China last year that Kayrros attributed to the nation’s coal sector.Unlike leaks and releases from natural gas and oil operations,  methane emissions from coal mines tend to be steady and continuous. That’s because workers vent mine gas from underground shafts as a safety precaution — getting rid of flammable gas to reduce the risk of explosions. In regions like Shanxi, where there are hundreds of emissions sources located close to each other, its more difficult to detect and quantify emissions compared with oil and gas ultra-emitters in remote areas. 

Like many other countries, including the U.S. and Canada, China doesn’t always require companies to report when they release methane. Shanxi’s Department of Ecology and Environmental and a spokesperson for the provincial government didn't respond to requests for comment. The Ministry of Ecology and Environment, which regulates provincial and regional emissions, and the National Development and Reform Commission, which oversees energy companies, didn’t reply to questions.Methane can be captured as it seeps from underground mines and sold or used to generate power. If it’s released without being combusted, the potent greenhouse gas traps 84 times more heat in its first 20 years in the atmosphere than carbon dioxide.

Learn more about the planet-warming power of methane:

Scientists are only just beginning to use satellite data to estimate how much methane is coming from coal-mining operations around the world. In November, Dutch researchers said their analysis of coal mines in Australia’s Bowen Basin suggested that there may be “large underreporting of methane emissions in the national inventory.”China is the world’s largest producer and consumer of coal, and the sector is the nation’s biggest opportunity to cut methane emissions, according to a United Nations assessment. There are signs that Beijing plans to tackle the issue more aggressively. The country’s latest five-year plan includes its first-ever pledge to reduce methane.

While China declined to join an international effort to curb methane led by the U.S. and EU, it has said it’s working on a plan to contain emissions. The global methane pledge is non-binding and doesn’t assign specific reductions to countries. President Xi Jinping has also said the country reduce coal use starting in 2026, on its way to a broader goal of reaching peak greenhouse gas emissions by the end of the decade and carbon neutrality by 2060.

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