In Decatur, Ill., far from the coal mines of Appalachia, Caterpillar engineers are working on the future of mining: mammoth haul trucks that drive themselves. The trucks have no drivers, not even remote operators. Instead, the 850,000-pound vehicles rely on self-driving technology, the latest in an increasingly autonomous line of trucks and drills that are removing some of the human element from digging for coal. When President Trump moved on Tuesday to dismantle the Obama administrations climate change efforts, he promised it would bring coal-mining jobs back to America. But the jobs he alluded to hardy miners in mazelike tunnels with picks and shovels have steadily become vestiges of the past. Pressured by cheap and abundant natural gas, coal is in a precipitous decline, now making up just a third of electricity generation in the United States. Renewables are fast becoming competitive with coal on price. Electricity sales are trending downward, and coal exports are falling. 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 its 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 Institutions 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.