According to multiple news reports, President Donald Trump will sign an executive order on Tuesday telling the Environmental Protection Agency to begin rolling back a variety of Obama-era policies on climate change in an effort to aid the coal and oil industries.

“The executive order,” Trump’s EPA Administrator Scott Pruitt told ABC on Sunday, “will address the past administration's efforts to kill jobs across this country through the Clean Power Plan.” (Note that the evidence that climate regulations have significantly affected overall employment is awfully thin.)

While we don’t have the full text of the order yet, both Bloomberg and the Washington Post report that it will direct Pruitt to begin rewriting Obama-era rules that regulate carbon dioxide from both new and existing power plants. The latter, known as the Clean Power Plan, aimed to reduce CO2 emissions from the electricity sector some 32 percent below 2005 levels by 2030.

Pruitt can’t just repeal these rules by fiat. He has to go through the formal rulemaking process, which entails proposing entirely new rules to replace Obama’s versions, posting them for public comment, responding to all those public comments, and then defending his new rules in court. He’ll have to make sure any new rule complies with the Clean Air Act — which, thanks to a 2007 Supreme Court ruling and a 2009 EPA endangerment finding, now requires the EPA to regulate carbon dioxide. The whole process could take years, and he might face setbacks in court.

In an earlier post, I described some ways Pruitt might try to rewrite the Clean Power Plan. One possible option is to make it far less expansive, so that it merely requires incremental efficiency upgrades at existing coal plants rather than pushing for deeper reductions, as Obama’s rule did. But again, Pruitt will have to make the rule legally defensible, and he’s certain to be challenged by green groups, which are very skilled at this kind of litigation.

Trump’s order will also reportedly insist on other changes, such as revamping the White House’s estimate of the social cost of carbon — a measure of the damage caused by climate change that’s incorporated into agency cost-benefit analyses of new pollution regulations. The order will also likely lift a moratorium on leasing new coal from public lands that the Interior Department put in place under Obama while it reviewed its leasing policies. And it will push to repeal rules on methane leaks from oil and gas drilling on public lands.

The order is not expected to say anything about whether the US will stay in or pull out of the Paris climate deal, and it won’t ask Pruitt to try to rescind the EPA’s fundamental authority to regulate greenhouse gases as a threat to public health and welfare. (That authority would be very difficult to repeal, given that the scientific evidence that greenhouse gases cause damage through climate change is very strong.)

We’ll have much more on this executive order when it comes out, but for now it’s enough to say that this is just a first salvo in the new administration’s multi-year war on climate policy — a war with an outcome that’s still very much uncertain.

Further reading

— A look at why Trump is unlikely to bring back all the coal-mining jobs that have vanished — even if he does repeal the Clean Power Plan.

— This interview with Harvard’s Jody Freeman delves into all the obstacles Trump and Pruitt may face in trying to repeal EPA regulations.

— Two big ways Trump could try to undo Obama’s Clean Power Plan.