Last year saw U.S. coal-fired generating capacity drop by an estimated 13.7 gigawatts (GW), and the first five days of 2020 suggested the fuel’s fortunes will only continue to shrink. By Jan. 5, 2020, two of the four generating units at Montana’s Colstrip Power Plant burned through the last of their coal supplies and ceased operations. This process is expected to play itself out at a number of U.S. coal plants this year, as King Coal cedes its crown to natural gas and renewables.

As of early January, research firm S&P Global Market Intelligence estimated planned 2020 coal plant closures could total 9 GW. This figure could merely be a starting point, and the Colstrip plants serve as a good example why. The two units, with a combined capacity of 614 MW, were expected to close by 2022; however, co-owners Talen Energy and Puget Sound Energy announced in July that the units would close sooner because of rising coal prices. So, it’s obvious that estimates this early in the year may understate actual closures.

The cost of environmental retrofits for a largely aging coal fleet is certainly part of the equation behind the fuel’s falling fortunes. There’s also the fact that natural gas, wind and solar are simply cheaper, even without factoring in those improvements. The Montana Consumer Counsel, a state consumer-advocacy agency, estimated customers paid $73.85 per MW-hour for power from Colstrip Unit 4 in 2017, compared to $31 or less for power from a nearby wind farm.

Similar economic arguments played out in 2019, which saw a number of particularly large coal plants cease operations. These included the three units of the Navajo Generating Station, Page, Ariz., totaling 2,250 MW; two units at the Bruce Mansfield Generating station, Beaver County, Pa., (1,660 MW); and two units at the Consesville Generating Station, Coshocton County, Ohio, (750 MW).

In total, a January report from the Rhodium Group estimates coal generation fell by 18% last year, which is more than 2018’s total. This drop is simply another data point in a trend that has been built over the last decade. U.S. coal generation peaked in 2007, according to the U.S. Energy Information Administration, totaling 313 GW. By 2018, it fell to a low last seen in 1975. That year, the U.S. gross domestic product was $1.6 trillion, according to the World Bank. It reached $21.4 in 2019, according to the World Bank, which emphasized how much less significant coal generation has become to the U.S. economy.

There are environmental benefits to the plant shutdowns. Rhodium Group researchers say last year’s plant closures are responsible for a 10% reduction in greenhouse gas emissions related to power generation—even with natural gas making up some of that lost generating capacity. That helped drive down total U.S. emissions by 2.1%. In fact, the power sector, which accounts for 27% of net emissions, leads other industries in its decarbonization efforts.

As electricity production becomes greener, pressure could mount to switch users to electrification and away from fossil fuels. Transportation exceeds power generation in emissions production and is becoming an easy target for a move away from petroleum products such as gasoline, diesel and jet fuel. Similarly, building-related emissions grew by 2.2% last year, according to Rhodium Group, which could push incentives for electrified heating and cooling equipment.

President Donald Trump has pledged to remove the United States from Paris Climate Accord on climate change by the end of this year, but a number of states and municipalities are holding firm to its provisions. This means pressure will remain high on many utilities to reduce coal production further.

Of course, coal plants are also employers, so these closures have real economic implications for workers and their communities. The two shuttered Colstrip units employed about 100 workers, according to the Billings Gazette. The newspaper calls the plant and adjacent mining operation the anchor for the surrounding community and region. The Navajo Generating Station and its adjacent coal mine employed 750 people, almost all Native American, before both operations began shutting down in 2016.

Operations continue at Colstrip’s units 3 and 4, but their future—like that of many other still-operating coal facilities—is in question. Two of the plants’ four utility owners plan to drop their ownership stake by 2025. Based in Washington and Oregon, these companies face state laws banning coal power after that date. NorthWestern Energy, which serves Montana and South Dakota, is seeking to boost its ownership stake in at least Unit 4 and keep it running through 2042. But recent history indicates that any forecasts stretching out more than two decades should be taken with a grain of salt—or, perhaps more appropriately, a lump of coal.