Trump had previously been mostly mute on details of his energy policy, but had been skeptical of climate change and the Paris agreement. Environmental advocates and Clinton have criticized his stance for underplaying the economic and social risks of climate change.
Clinton, among other proposals, has said she wants to reduce U.S. dependence on coal and limit hydraulic fracturing, or fracking. Those actions would follow the Obama administration's policies, which include regulating emissions from coal-fired power plants and increasing renewable energy use.
Most scientists acknowledge the role of fossil fuel use in climate change.
Coal's importance as an energy source has diminished amid cheap natural gas prices and slowing demand abroad. In his comments to reporters Thursday, Trump contended that regulations have contributed to the industry's struggles as well as market forces.
"All I can do is free up coal," Trump said. "Market forces are something I don't want to get involved with."
David Sandalow, a former U.S. undersecretary of energy, told CNBC's "Power Lunch" on Thursday that simultaneously saving the coal industry and boosting natural gas production could be difficult.
"[Trump] said he's going to put coal workers back to work but hasn't told us how. And at the same time, he said he's going to increase hydraulic fracturing, which is the main reason that prices have gone down for natural gas and that's what put coal miners out of work," said Sandalow, who is now the inaugural fellow at the Columbia University Center on Global Energy Policy.
Trump's positions are further complicated by a recent Politico report that shows his organization cited global warming as justification to build a coastal structure to prevent erosion at a golf course in Ireland.
— Reuters contributed to this report.