Coal miners wave signs as Donald Trump speaks during a campaign rally in Charleston, W.Va., on May 5. (Steve Helber/Associated Press)

IT IS hard to say exactly what impact President-elect Donald Trump might have on the fight to slow human-caused climate change — for two reasons. 

First is that Mr. Trump has not been particularly clear on his views, though he leaves little reason for hope. He has at times sounded like a wholesale climate denier and conspiracy theorist, such as when he claimed global warming is a hoax. At other times he has taken a slightly more conciliatory tone. The last word the country has had from the next president was widely interpreted as falling into the latter category; he told the New York Times that “there is some connectivity” between human action and the warming of the planet and that he is keeping “an open mind” on the matter. 

The reaction to Mr. Trump’s latest statement was almost certainly too optimistic: Mr. Trump also claimed that “I’m not sure anybody is ever going to really know” what the facts on climate change are, though the scientific community has dedicated decades of study to the issue and is near-unanimous in its concern. Mr. Trump also promised to cancel “job-killing” energy regulations in a post-election YouTube video, and his incoming chief of staff, Reince Priebus, assured Fox News viewers that his “default position” is that “most of it is a bunch of bunk.” All that suggests Mr. Trump is unlikely to treat global warming as the threat it is and that he will favor fossil fuel interests when he is in the White House.

How that translates into policy changes, however, is also unpredictable — and offers slightly more reason for hope. Reversing federal rules takes time and sustained effort, and courts do not always allow regulatory changes. Congress could help Mr. Trump gut environmental protections, but the Senate, with its narrow Republican majority, may balk.  The George W. Bush administration was pretty favorable to fossil fuels, but, for all its effort, it failed to change many enduring environmental programs. 

The United States is still on track to lower its emissions in a way that could maintain some of its credibility on the international stage, in part because utilities have substituted cheap natural gas, which Mr. Trump favors, for coal. That trend, along with a continuation of federal renewables subsidies already written into law and the progress of various state-level efforts, will put downward pressure on the country’s carbon emissions. These factors are not nearly enough to transition off dirty energy in the long run, but they do mean that even if Mr. Trump foolishly defies the warnings of experts, there may be ways to limit the damage over the next four years. 

Given that Mr. Trump does not want to undermine the success of natural gas, that he cannot control the actions of states and cities, and that he will not eliminate every pro-renewables policy on the federal level, the next administration should ask itself why it would pull out of the Paris agreement, an international climate deal that took decades to strike. Doing so would relieve pressure on China, India and other big emitters to contain their emissions. If the United States is going to constrain its carbon footprint, anyway, why let other countries off the hook?