Of all Donald Trump’s Cabinet picks, it’s hard to find anyone who’s been more overtly hostile toward the agency he’s about to lead than Scott Pruitt has been toward the Environmental Protection Agency.

Pruitt made no secret of this; during his tenure as Oklahoma’s attorney general, his bio page called him “a leading advocate against the EPA’s activist agenda.” Over the last six years, Pruitt has filed lawsuit after (mostly unsuccessful) lawsuit to halt EPA rules on mercury pollution from coal plants, thwart EPA plans to clean up the Chesapeake Bay, block President Obama’s efforts to tackle climate change — and much, much more.

Pruitt’s record is so stark that nearly 800 former EPA employees signed a letter opposing his confirmation. They criticized Pruitt’s cozy ties with Oklahoma’s oil and gas industry, his opposition to the federal government regulating air pollution that crosses state lines, his history of downplaying global warming. “Mr. Pruitt’s record,” the letter states, “raises serious questions about whose interests he has served to date and whether he agrees with the longstanding tenets of U.S. environmental law.”

But none of this was enough to derail Pruitt’s nomination. Trump wanted an EPA head who would roll back Obama’s climate policies. And the modern-day GOP is in sync with Pruitt’s views on environmental regulation — namely, that the feds should do less of it. Pruitt also enjoyed widespread support among industry groups and conservatives, who have been running ads in his favor for months.

So, on Friday afternoon, the Senate confirmed Pruitt, with support from 50 Republicans (Susan Collins was the lone “no”) plus two Democrats (Joe Manchin and Heidi Heitkamp). Democrats tried to delay the vote until after Oklahoma released Pruitt’s email correspondence with the fossil fuel industry, but they were unsuccessful.

The big question now is how far Pruitt will actually go to reshape the nation’s environmental policies. It’s possible he’ll face intractable obstacles in trying to shrink the EPA’s reach over the next few years, hemmed in by various legal constraints and pushback from career staff. But it’s also possible that he’ll roll back the EPA’s climate policies and make it much, much tougher for both the United States and the world to tackle global warming for years to come. If the latter comes to pass, Pruitt could end up being one of Donald Trump’s most consequential Cabinet picks.

Pruitt will have a lot of power to change the EPA — but also faces serious obstacles

The EPA, an $8 billion agency with 15,000 employees, is tasked with enforcing laws on everything from air pollution to chemical safety. It’s guided by major statutes like the Clean Air Act and Clean Water Act, which often require the agency to update its regulations regularly to reflect new science on pollution and public health.

The EPA’s political leadership has some latitude in deciding whether these rules should be stronger or weaker, but they have to work within the confines of those statutes. Under President George W. Bush, the EPA tried to issue relatively lax rules on smog and mercury pollution. But green groups sued, and those efforts got slapped down in court. The Obama administration later issued much more stringent smog and mercury rules, as well as ratcheting up dozens of other regulations, particularly on coal plants.

The EPA is also now the key US agency dealing with climate change. In 2007, the Supreme Court ruled that the EPA had authority to regulate greenhouse gases under the Clean Air Act if it determined they pose a threat to public health or welfare. Obama’s EPA determined they do pose a threat, and went about enacting a flurry of climate policies: stricter fuel economy standards for cars and trucks; limits on CO2 from new and existing power plants; regulations on methane leaks from oil drilling.

Pruitt clearly thinks Obama’s EPA went too far on these fronts, arguing at his Senate confirmation hearing that the agency “became dissatisfied with the tools Congress had given it … and bootstrapped its own powers and tools through rulemaking.”

Over the past six years, the courts have usually disagreed, rejecting many of Pruitt’s lawsuits and upholding EPA actions. But as EPA administrator, Pruitt will now have much greater leeway to set policy. Here are a few broad actions he can take:

Rewrite and weaken some of Obama’s EPA rules. Rewriting existing EPA regulations is a tricky, multiyear process that requires going through formal rulemaking procedures. But Pruitt could, for instance, revamp Obama’s Clean Power Plan to require far less extensive CO2 cuts from power plants. He could redo the EPA’s “Waters of the US” rule so that the Clean Water Act applied to fewer streams and wetlands. Because rewriting rules is so time-intensive, “there’s limited bandwidth here,” says Jeffrey Holmstead, a top EPA official in the George W. Bush administration. “But if I had to guess, I’d guess they get a couple of these big changes done.”

Rewriting existing EPA regulations is a tricky, multiyear process that requires going through formal rulemaking procedures. But Pruitt could, for instance, revamp Obama’s Clean Power Plan to require far less extensive CO2 cuts from power plants. He could redo the EPA’s “Waters of the US” rule so that the Clean Water Act applied to fewer streams and wetlands. Because rewriting rules is so time-intensive, “there’s limited bandwidth here,” says Jeffrey Holmstead, a top EPA official in the George W. Bush administration. “But if I had to guess, I’d guess they get a couple of these big changes done.” Delay the development of new rules. Under the Clean Air Act, the EPA is eventually supposed to regulate other sources of greenhouse gas emissions beyond cars and power plants — including refineries, chemical plants, and so on. Pruitt could delay the introduction of additional climate rules indefinitely.

Under the Clean Air Act, the EPA is eventually supposed to regulate other sources of greenhouse gas emissions beyond cars and power plants — including refineries, chemical plants, and so on. Pruitt could delay the introduction of additional climate rules indefinitely. Scale back enforcement of existing regulations. As attorney general of Oklahoma, Pruitt disbanded the state’s Environmental Enforcement Unit. At the EPA, he could direct the agency to be less aggressive about investigating companies for pollution violations, bringing fewer cases to the Department of Justice.

As attorney general of Oklahoma, Pruitt disbanded the state’s Environmental Enforcement Unit. At the EPA, he could direct the agency to be less aggressive about investigating companies for pollution violations, bringing fewer cases to the Department of Justice. Give more deference to the states. Many US pollution rules are developed by the EPA but implemented by state agencies — the EPA approves state implementation plans and steps in if they’re not being assertive enough. Pruitt has long insisted he’d like the EPA to be more deferential to state agencies, an approach he calls “cooperative federalism.” (Critics of this approach worry that state agencies are often overly lenient on industry, and that states struggle to deal with pollution that crosses state lines.)

Many US pollution rules are developed by the EPA but implemented by state agencies — the EPA approves state implementation plans and steps in if they’re not being assertive enough. Pruitt has long insisted he’d like the EPA to be more deferential to state agencies, an approach he calls “cooperative federalism.” (Critics of this approach worry that state agencies are often overly lenient on industry, and that states struggle to deal with pollution that crosses state lines.) Change the way the EPA uses science. The EPA’s scientific advisory boards are tasked with synthesizing the latest science on pollution and public health so that regulations can be updated regularly, as the law requires. The Bush administration tended to stock these advisory boards with more industry-friendly voices — and sometimes ignored their recommendations altogether. This will be something to watch in Pruitt’s EPA.

The EPA’s scientific advisory boards are tasked with synthesizing the latest science on pollution and public health so that regulations can be updated regularly, as the law requires. The Bush administration tended to stock these advisory boards with more industry-friendly voices — and sometimes ignored their recommendations altogether. This will be something to watch in Pruitt’s EPA. Push to shrink the EPA’s budget. Pruitt will also help shape the Trump administration’s budget requests to Congress, and he could ask to shrink parts of the agency. Republican lawmakers have signaled they’d be happy to oblige. Budget cuts could further hamstring the agency’s ability to enforce regulations and develop new rules. (Congress has already been whittling down the EPA’s budget since 2011, and prosecutions for environmental crimes have fallen by half during that time.)

Now, there are limits to how far Pruitt can go. If his EPA starts missing statutory deadlines, or sidesteps rule-making procedures, or issues rules wildly out of step with what the Clean Air Act requires, he’ll be stopped in court. America’s environmental laws are unique in offering ample opportunity for outside groups to sue, and green groups like the Sierra Club and Natural Resources Defense Council are deft in using this to their advantage — they blocked dozens of Bush and Reagan-era deregulatory moves.

So, for instance, it’s unlikely that Pruitt could tear up the EPA’s Endangerment Finding, the 2009 analysis establishing that greenhouse gases were a threat and therefore need to be regulated, without Congress. “That has a voluminous scientific foundation behind it,” said Jody Freeman, a Harvard law professor and former Obama climate adviser. “The Trump administration couldn’t just come in and say, ‘Nope, no more endangerment!’ There’s almost no chance that would be upheld [in court].”

But Pruitt is familiar with environmental laws and is likely to pick his battles carefully, says Holmstead. And green groups won’t be able stop everything he might want to do — like pulling back on environmental enforcement at oil and gas facilities (something Obama’s EPA prioritized). “It’s extremely difficult to challenge an agency on enforcement decisions,” says Emily Hammond, a law professor at George Washington University. “Courts tend to treat that like prosecutorial discretion.”

Pruitt’s most sweeping impact could be on climate change policy

If you want to see how Pruitt’s tenure at the EPA might play out, you should read this New York Times piece from 1989, written at the end of Ronald Reagan’s presidency. Like Trump, Reagan came to office hoping to dismantle the EPA and make life easier for industry. Environmentalists feared the worst, as they do with Pruitt now.

Things didn’t exactly work that way. As Philip Shabecoff wrote in his Times look-back, the end result after eight years was a “stalemate.” To the disappointment of many conservatives, Reagan didn’t radically reshape the EPA, in part because his political appointees made some serious missteps, in part because they were beaten back in court. The agency was left “more or less intact.”

Yet Reagan’s appointees still had a real impact: “Environmental and conservation agencies were starved for money, the agencies were politicized and their staffs were demoralized, critics say. Worst of all, they say, the Government deliberately delayed attacking long-term problems like global warming linked to pollution, acid rain, toxic waste, air pollution and the contamination of underground water supplies.”

A similar four- or eight-year delay today could prove even more fateful — thanks to the growing urgency around global warming. After years of dithering on climate policy, the world now has precious little time to slash emissions and avoid what world leaders consider a dangerous 2°C or even 3°C rise in global average temperatures.

During the Obama years, the US and the rest of the world were starting to make slow, fragile process on addressing this issue. The Obama administration set a goal of cutting US emissions at least 26 percent below 2005 levels by 2020 and hoped that various EPA rules — including the Clean Power Plan and limits on methane leaks — would get us there. These rules helped underpin the Paris climate agreement, under which all countries agreed to tackle their own emissions and ratchet up ambitions over time.

Trump and Pruitt, of course, want to roll back many of those EPA rules. Obama’s version of the Clean Power Plan (which is currently being challenged in court) would’ve prodded many states to shift from coal to cleaner gas and renewables. Pruitt’s version might merely require coal plants to slightly improve their heat-rate efficiency, leading to far fewer emission cuts. Similarly, Pruitt has suggested he might block California’s request to strengthen its clean car rules under the Clean Air Act — rules that have had a big impact on the US electric car market. And so on.

It’s hard to predict exactly how much these actions will matter. One possibility is that they won’t. Perhaps states will continue to shift away from coal and invest in renewables anyway, partly for economic reasons and partly because they know carbon cuts will be inevitable someday. (Emily Holden of E&E News has a great interview with an Arkansas regulator who notes that utilities are planning CO2 cuts because they expect the next president after Trump will push for stricter climate rules.) Perhaps electric cars will continue to catch on, as battery prices drop.

But it’s also quite plausible that Pruitt’s tenure at EPA could derail momentum on decarbonization in a way that will have major, long-term repercussions. Perhaps he works with Congress to strip away the EPA’s authority over greenhouse gases once and for all, so that no future president can act. Perhaps the US fails so miserably to hit its emissions targets that other countries start winding back their own climate ambitions, leading to a hotter planet overall.

There are so many different factors at play, and the future is uncertain. But it’s hardly inconceivable that decades from now, as the planet keeps warming, we could look back and see picking Scott Pruitt as one of Trump’s more momentous decisions.

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