PNNL

The Science

Coal mines are one of the largest sources of methane emissions from human activities. As the world produces more coal, coal mines get deeper every year, and methane emissions grow with the increasing mining depths. Mine operators also abandon old coal mines, and the coal strata in these abandoned mines still emit methane into the atmosphere.

A study, led by researchers at the U.S. Department of Energy’s Pacific Northwest National Laboratory, included a detailed modeling of future methane emissions from active and abandoned mines. Based on a detailed analysis of current and past mine emissions, increasing mine depth, and other factors, the researchers concluded that future methane emissions from these mines will likely be significantly higher than previous studies have found.

The Impact

The current study estimates methane emissions from underground and surface coal production while accounting for the increase in mining depth using several new and compiled data sets. It is also the first attempt to estimate global methane emissions from abandoned coal mines through 2100 under different coal production scenarios. This study estimates that total methane emissions from coal mining are higher than previous studies report.

More importantly, the study results indicate that emissions from the growing population of abandoned mines increase faster than those from operating mines. Abandoned mine methane emissions continue through the century, even with aggressive mitigation actions. More accurate projections of future emissions from coal mines can provide a better understanding of the economic potential of methane as an energy resource. The results of this study can also be used in emission models to more accurately account for fugitive emissions from coal mines.

Summary

This study was born out of discussions of emissions and mine depth during Global Methane Initiative’s Coal Subcommittee meetings. PNNL worked with U.S. Environmental Protection Agency specialists and mining experts to collect data about the gas content of different coal ranks from several continents and analyze measurement data about coal production, mine depth, and methane emissions from key coal-producing countries. The team also conducted a thorough literature review and presented the preliminary results at several international forums.

Using coal production data from six integrated assessment models, this study indicates that by 2100 methane emissions from active underground mines could increase by a factor of 4, while emissions from abandoned mines could increase by a factor of 8. Even if aggressive mitigation actions are taken, methane emissions still continue from abandoned mines. The study concludes that future methane emissions will likely be significantly higher than those reported in previous studies, methane resources at abandoned mines will grow regardless of future coal production, and our research data sets may provide insights for improving future emissions inventories.

Contacts

Meredydd Evans
Team Lead, Human-Earth Systems Science: Decisions
m.evans@pnnl.gov

Nazar Kholod
Scientist, Human-Earth Systems Science: Decisions
nazar.kholod@pnnl.gov

Funding

This study is funded by the U.S. Environmental Protection Agency and the Global Methane Initiative (agreement DW-89-92403301-4).