The use of coal in the U.S. has fallen by 44 percent in the last decade, with 2018 consumption projected to be 437 million short tons lower than the 2007 peak, according to the EIA.

The drop is largely due to the decline in the coal power market spurred by cheap natural gas.

Utility companies, by the end of 2017, had retired 529 of the 1,470 coal-fired generators operating in 2007. Many of those retirements were for old, less efficient units. The EIA notes that a federal rule to reduce mercury and air toxics in 2015 drove many of those retirements as utilities chose to close older units rather than invest in compliance with the new standards.

Mercury is released into the air from burning coal. Exposure can cause neurological disorders as well as respiratory problems.

The Trump administration proposed a rollback of the mercury standards just last week. Most utilities say they have already absorbed the cost of the new mercury standards or made retirement decisions.