Reported emissions from the Underground Coal Mines sector decreased from 40.9 million metric tons (MMT) CO₂e in 2011 to 34.2 MMT CO₂e in 2019, a decline of 16.4 percent. Emissions were relatively steady from 2011 and 2015 but began gradually decreasing beginning in 2016. The reported emissions in 2019 continued this downward trend with emissions decreasing by 1.7 MMT CO₂e (4.7 percent) compared to 2018. The declining trend in emissions is attributed to a nationwide decrease in coal production combined with the idling or closure of several large, gassy underground mines. The number of reporters decreased from a high of 131 in 2014 to a low of 67 in 2019.  The decrease in the number of reporters is largely due to the closure of several mines but is also attributed to 2016 amendments in Part 98 allowing underground coal mines to cease reporting for abandoned mines. Prior to 2016, owners and operators were required to continue reporting for up to three years following abandonment. The number of underground coal mines reporting dropped from 125 in 2015 to 95 in 2016 due, in part, to this rule amendment.