Across the US, a major, uncontrolled leak of a potent greenhouse gas is going unregulated and largely unnoticed.<p>Climate Home News analysis of government data has identified roughly 300 active and 200 abandoned coal mines, which are the source of almost one-tenth of US methane pollution.<p>Methane has 34 times the long-term warming effect of carbon dioxide and accounts for 10% of US greenhouse gas emissions. Its emissions from the oil and gas industry and the efforts of the Trump administration to roll back regulations on them have been widely publicised.<p>Meanwhile, US coal mines released 60.5 MMTCO2e of methane in 2016, with roughly the same warming impact as 13 million cars. Efforts to control the problem are being hampered despite those with the technical expertise claiming a whole industry could be built on capturing these emissions and turning them into electricity.