All the while, the coal industry has been replacing workers with machines and explosives. Energy and labor specialists say that no one — including Mr. Trump — can bring them all back.
“People think of coal mining as some 1890s, colorful, populous frontier activity, but it’s much better to think of it as a high-tech industry with far fewer miners and more engineers and coders,” said Mark Muro, senior fellow at the Brookings Institution’s Metropolitan Policy Program.
“The regulatory changes are entirely outweighed by these technological changes, not to mention the price of natural gas or renewables,” Mr. Muro said. “Even if you brought back demand for coal, you wouldn’t bring back the same number of workers.”
Estimating the employment gains and losses from moves to regulate greenhouse emissions has become a political exercise.
The U.S. Chamber of Commerce, which has opposed against carbon regulations, warned that former President Barack Obama’s signature Clean Power Plan would lead to an average loss of more than 200,000 American jobs each year through 2030 — a wildly overstated projection, energy and labor specialists say.
The Obama-era plan, the effort Mr. Trump has vowed to dismantle, would have closed hundreds of coal-fired power plants, frozen construction of new plants and replaced them with vast new wind and solar farms. Mr. Obama had pledged as part of the Paris climate pact that the United States would cut its emissions about 26 percent from 2005 levels by 2025, and carrying out the Clean Power Plan was essential to meeting that target.
Environmental groups have given bold estimates of their own, arguing that jobs related to clean energy and energy efficiency would increase under the plan — by as many as 274,000 through 2020, according to the Natural Resources Defense Council.
The Environmental Protection Agency, meanwhile, estimated that the plan would lead to a gain of as many as 80,000 jobs by 2020.
None of those estimates have even begun to be tested. The power plan from the Obama administration had not been put into effect because it had been blocked by the Supreme Court.
Part of the difficulty in forecasting the employment fallout is the many variables involved: prices of coal and gas, the projected growth and cost of renewable energy, and jobs generated by energy efficiencies.
Even coal executives remain muted in their optimism about the Clean Power Plan rollback, which they say is nowhere near enough to return coal to its dominant perch atop power markets and put tens of thousands of coal miners to work.
Then there is the technology.
Caterpillar’s autonomous trucks are already being used at mines in Western Australia. “An autonomous truck doesn’t need to stop for lunch breaks or shift changes,” Caterpillar said in a promotional page on its website. And it is proceeding with semiautonomous drills, including a system that lets one worker control three drills at once.
A shift from underground coal mines to surface mines — which involves opening mountains with controlled explosions, then using automated heavy machinery to mine the coal — has also led to a decline in mining jobs.
In 1980, the industry employed about 242,000 people. By 2015, that figure had plunged 60 percent, to fewer than 100,000, even as coal production edged up 8 percent. Helped by automation, worker productivity more than tripled over the same period, according to data from the federal Energy Information Administration and the Brookings Institution.
And a recent study by the International Institute for Sustainable Development and the Columbia Center on Sustainable Investment predicted that automation was likely to replace 40 to 80 percent of workers at mines.
Automation makes mines more “safe, efficient and productive,” said Corrie Scott, a Caterpillar spokeswoman. “While mines would not need as many drivers, they will need more people who use and understand the latest technology,” she said.
“However way you spin it, gas and renewables are going to continue to replace coal,” said Nicolas Maennling, senior economics and policy researcher at Columbia University and an author of the automation study.
“And in order to stay competitive, coal will have to increase automation,” he said. “What Mr. Trump does will make little difference.”