The amount of methane emissions released into the atmosphere due to coal mining is likely much higher than previously calculated, according to research presented at the annual meeting of the American Geophysical Union recently.
The study estimates that methane emissions from coal mines are approximately 50 per cent higher than previously estimated.
The research was conducted by a team at the U.S. Department of Energy’s Pacific Northwest National Laboratory (PNNL), the U.S. Environmental Protection Agency and others.
The higher estimate is due mainly to two factors: methane that continues to be emitted from thousands of abandoned mines and the higher methane content in coal seams that are ever deeper, according to chief author Nazar Kholod of PNNL.
The results have important implications for Earth’s climate because methane is approximately 25 times more powerful than carbon dioxide when it comes to warming the planet over a long period.
In addition to coal mining, other major sources of methane emissions globally include wetlands, agriculture, and oil and gas facilities.
The study is the first to attempt to account for methane escaping from abandoned mines. The reason is straightforward, Kholod said: Good data sets are hard to come by.
His paper drew largely on data from the United States and Ukraine, countries where data about coal mine status and methane is fully available.
In the United States in 2015, about one-third of abandoned mines were flooded. Ukraine reported that all its mines abandoned that year were flooded.
The team estimated that in 2010, 103 billion cubic metres of methane were released from working underground and surface mines and an additional 22 billion cubic metres from abandoned mines.
That total of 125 billion cubic metres for 2010 is 50 per cent higher than the estimate of 83 billion cubic metres for that year by the Community Emissions Data System, a highly regarded system developed by PNNL researchers and collaborators used for analysing historical emissions data.
While the results are based on actual measurements from coal mines around the world, the scientists suggest further studies that consider more measurements from coal mines, including abandoned mines, would be helpful.
The study analysed future methane emissions from coal mines under a range of scenarios. If efforts to address climate change resemble what they have been, the researchers estimate that methane emissions as a result of coal mining will increase dramatically by the end of the century: Nearly eight times what they are today from abandoned mines and four times what they are from working mines.
But Nazar notes that there is uncertainty about future coal production. If coal production decreases, then emissions from working mines would decrease.
However, in all scenarios, methane emissions from abandoned mines are expected to grow more quickly than those from established mines. The team cites deeper mines, more abandoned mines, and a greater percentage of surface mines from which methane escapes more freely as reasons why.
Those increases are significantly higher than what current climate models call for – for instance, 83 per cent higher in 2050 than suggested by the widely used Global Change Analysis Model developed by PNNL.
The study estimates that if strong climate mitigation strategies are put in place, then by the end of this century the amount of methane escaping from abandoned mines would be about the same as 2020.
Under the same conditions, the amount of methane escaping from working mines would be cut in half.
“If you stop producing coal, that doesn’t mean that methane will stop being emitted from coal mines,” said Kholod. “We can’t just take coal out of the equation.”
JGCRI scientist Meredydd Evans is also an author of the paper. Other authors include Raymond Pilcher of Raven Ridge Resources of Grand Junction, Colo.; Volha Roshchanka and Felicia Ruiz of the EPA; and Michael Coté and Ron Collings of Ruby Canyon Engineering of Grand Junction, Colo.
The research was funded by the EPA and the Global Methane Initiative.