U.S. coal consumption in 2018 is expected to hit the lowest level in 39 years, the U.S. Energy Information Administration (EIA) said on Tuesday.

According to the EIA, the total U.S. coal consumption in 2018 would fall to 691 million short tons (1 short ton is about 0.9 metric ton), a 4 percent decline from 2017 and the lowest level since 1979.

U.S. coal consumption has been falling since its peak in 2007, and 2018 coal consumption is expected to be 44 percent lower than the 2007 level, according to the EIA.

The EIA said declines in coal use in the electric power sector, the nation's largest consumer of coal, have contributed to the decrease the most. From 2007 to 2017, almost 36 percent of coal-fired generators had retired. And more coal-fired plants are expected to retire in 2018, which will further reduce coal consumption.

The EIA expected power sector coal consumption to fall 4 percent in 2018 and 8 percent in 2019.

Increased competition from natural gas and renewable sources has also reduced coal's market share and facilitated coal retirements. Natural gas prices have stayed relatively low since U.S. domestic natural gas production began to grow in 2007.

Moreover, environmental concerns have played a role in coal retirements.