In the final days of the Obama administration, scholars and journalists took stock of all that he had done to combat the dangerous rise of climate change. Barack Obama, they pronounced, had built up a surprisingly vast array of climate-concerned rules and guidelines across the government. He had turned the many policy-making tools of the many federal agencies toward preparing for this one imminent disaster.

Well, that was then.

On Tuesday, President Donald Trump will sign an executive order that will demolish his predecessor’s attempts to slow the pace of climate change. It is an omnibus directive that strikes across the federal government, reversing major rules that aim to restrict greenhouse-gas emissions while simultaneously instructing departments to ignore or downplay the risks of climate change in their decision-making.

It is exactly as bad as environmental advocates feared—with one exception. The order does not mention whether the United States should remain in the Paris Agreement, the international pact to address climate change ratified in 2015. Withdrawal from the treaty, a campaign promise of Trump’s, still divides his White House. (Reportedly, Jared Kushner and Ivanka Trump are partial to staying in the agreement.)

Yet unless there are major advances in technology, it will be difficult for the United States to meet its commitments under Paris without using rules similar to the current regulations.

As details of the order leaked to the public, nearly every environmental or climate-centric group castigated it as a costly step backward. Andrew Steer, the president and CEO of the World Resources Institute, said that the administration was “taking a sledgehammer to U.S. climate action.”

An administration official, speaking anonymously to reporters on Monday so as to preview the order, described it in softer terms, as something between a strategic reset and an adolescent rite-of-passage. “When it comes to climate change, we want to take our course and do it in our own form and fashion,” the official said.

There is a lot going on in the order: Months of rumored environmental action have been distilled into this document. Its policy goals can be separated into two categories. First, some policies require rule-making processes that Trump can only set in motion and point toward certain goals. The second group of policies are just executive directives reserved to the president. Trump can issue them by himself, just as Obama did, and they will enter force immediately.

The largest shift in U.S. climate policy contained in the order falls into the first category. President Trump will command the EPA to review and rewrite the Clean Power Plan, the signature climate policy of the Obama administration.

The Clean Power Plan sought to replace coal-fired power plants with natural-gas, solar, wind, and hydroelectric plants; the EPA and outside studies estimated that it would save more than 1 billion tons of carbon-dioxide emissions by 2030. The EPA also predicted that the plan would reap more than $55 billion in public-health benefits per year by 2030. The electricity sector is responsible for about 30 percent of U.S. carbon emissions.

To the Trump administration and its allies, the Clean Power Plan constituted the advance front of Obama’s “war on coal.” (Most energy economists say that the coal business is collapsing not because of recent regulations, but because domestic fracking has made natural gas cheap and plentiful.) Some Constitutional law scholars, including Laurence Tribe of Harvard University, argued that aspects of Obama’s rule amounted to executive overreach.

Trump cannot reverse the Clean Power Plan immediately, but he can tell the EPA what goals to pursue. The EPA must then revisit the science and policy justifying that rule and go through the arduous process of drafting a new one. (It took the Obama administration more than six years to issue the first version of the rule.) And throughout all that time, the Clean Power Plan will likely stay out of effect: It has been on pause since the Supreme Court stayed it in February 2016.

Other, smaller changes fall under this same category. Most of them apply to how the federal government manages the huge expanses of land that it owns west of the Mississippi River. Trump will order the Department of the Interior to reconsider rules restricting methane emissions from oil and gas sites. The Bureau of Land Management will also rewrite its rule regulating the use of fracking.

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The second-largest shift in U.S. policy will have far more immediate implications. Trump will decree that agencies across the federal government no longer have to account for climate change when reporting on the environmental impact of an action or project.

As part of this change, he will command the U.S. government to revise its “social cost of carbon,” an actuarial estimate of the societal damage wrought by every additional ton of carbon dioxide emitted into the atmosphere. The social cost of carbon is used to estimate when climate-mitigating policies are a good investment.

Right now, the U.S. government’s social cost of carbon is priced at about $37 per ton. By forcing it to account only for carbon’s social cost to the United States, and by changing how it calculates future inflation, advocates fear that a new social cost figure could dwindle to the single digits. By contrast, a team at Stanford University and the University of California Berkeley have argued since the Obama era that the “real” social cost of carbon should be $220 per ton.

Both of these changes can go into effect immediately. They will accompany a slew of other rapid policy shifts. Trump will lift Obama’s moratorium on new coal leases, allowing the federal government to sell the mining rights to untapped coal seams in Wyoming and Idaho. His order will also formally withdraw six Obama-era memoranda about climate change, including one that instructed federal agencies to begin planning for the deleterious effects of climate change.

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“None of the ornaments on their Christmas tree are surprising,” said Frank Rambo, the leader of the clean energy and air program at the Southern Environmental Law Center. Most leaders knew that these changes were on the way since November 9. Yet to see them all in one place was stirring—years of work, suddenly repealed or under threat.

Legal resistance will meet any attempt to roll back EPA climate regulations. The Supreme Court ruled almost a decade ago that the agency can regulate greenhouse gases under the Clean Air Act; two years later, the EPA announced that carbon dioxide poses a harm to the public. If the agency abandons basic climate science in order to weaken its rules, environmental groups will spring to litigate.

Rambo also said that the specific wording of the order—which will not be released until late Tuesday—would determine its legal authority. “Sometimes an executive order can sound very far reaching, but there’s some little caveat in there that makes it just another piece of paper,” he told me.

Trump’s supporters and policy writers were more effusive. “This is a great start, and it accomplishes most of the work at the EPA,” said Myron Ebell, who ran the EPA transition for the Trump administration but who has now returned to directing environmental policy at the Competitive Enterprise Institute. Ebell has long cast doubt on the mainstream consensus around climate change.

He said the remaining question was whether the EPA would withdraw the endangerment finding, the decision that carbon dioxide poses a threat to human health. “My feeling is the litigation to try to block the withdrawal of the power-plant rules could tell us really useful input on how to withdraw from Paris and pull out of the endangerment finding,” he told me.

The Trump administration says the order will bring about energy independence for the country and constitute regulatory relief for coal miners.

Neither of these arguments are backed up by fact, though. In the power sector, the United States has long been a net exporter of coal. Last year, it began to net-export natural gas as well. (America does depend on foreign petroleum—but the White House rolled back gasoline fuel-efficiency rules earlier this month.)

Meanwhile, The New York Times reports that the rule could extend the working life of some coal-fired power plants for up to a decade, but that many mining jobs still might vanish due to increased mechanization. Richard Murray, the founder and CEO of the coal giant Murray Energy, told Trump last week that he shouldn’t expect to see most coal jobs return.

“I suggested that he temper his expectations. Those are my exact words,” Murray told The Guardian. “He can’t bring them back.”

Ebell said the goal of the rule is to “prevent turning the heartland states into copies of the California economy. California, and to some extent New York and New England, have been the leaders in pursing energy-rationing policies in the name of climate.”

By energy-rationing, Ebell meant the replacement of existing coal plants with natural-gas facilities and renewables. “It forces the closure of the least expensive form of electricity,” he told me, meaning coal. “Most utilties would have decided to keep their coal power plants going had it not been for this looming regulatory regime.”

Since the advent of fracking, natural gas has been consistently cheaper than coal. Natural-gas plants also need fewer workers. “Because of the competitive price of natural gas and the declining price of renewables, continuing to drive carbon out makes sense for us,” Lynn Good, the chief executive of Duke Energy, told The Wall Street Journal on Monday.

Prominent environmental leaders from the Obama era condemned the announcement. “This is not just dangerous; it’s embarrassing to us and our businesses on a global scale to be dismissing opportunities for new technologies, economic growth, and U.S. leadership,” said Gina McCarthy, the EPA administrator during Obama’s second term, in a statement.

International leaders also spoke about the order. “I don’t know anyone who wants to breathe dirty air, who wants to worry about their water source, or who wants to leave a dangerous world to their children,” said Christiana Figueres, the former UN diplomat who led the Paris climate talks, in a statement. “And because we are all united by these common desires, I am optimistic that Paris will endure, with world leadership remaining resilient in its commitments to Paris.”