In short: the agency will no longer be able to regulate carbon pollution or greenhouse gases—though a couple of scenarios might prevent President Trump from getting his way.

In the landmark 2007 case Massachusetts v. EPA, the Supreme Court ruled 5-4 that carbon dioxide and other greenhouse gases qualify as air pollutants under the Clean Air Act and should be controlled if they endanger public health. When Barack Obama became president in 2009, the EPA found that greenhouse gases do, in fact, endanger human health and welfare and thus need to be regulated.

The EPA did not put a cap on all global warming gases, but focused on major sectors, including tailpipe emissions from vehicles, the smokestacks of power plants and emissions from oil and gas extraction. Revoking endangerment eliminates such rules and re-ignites the conservative anti-regulatory campaign that began in the Reagan era. Repealing the endangerment finding won’t happen without fights in court, but if the Trump administration finally wins its bid to end federal climate pollution regulation, states may move to curb emissions and expand efforts like the existing regional greenhouse gas initiative.

Pat Parenteau is an emeritus professor at Vermont Law and Graduate School and was EPA regional counsel under President Ronald Reagan. This interview has been edited for length and clarity.

JENNI DOERING: What are the likely consequences for public health and the climate of the EPA decision to rescind this finding?

PAT PARENTEAU: The consequences cannot be overstated, and they’re negative. By repealing the endangerment finding, you’re knocking out the foundation for all of the federal government’s regulation of carbon pollution and greenhouse gases, whether it’s oil refineries, cement plants—every source you can think of that’s putting this kind of pollution into the atmosphere. This removes the ability of EPA to regulate any of it.

When Trump announced this repeal of the endangerment finding at his press conference, he and EPA Administrator Lee Zeldin were bragging about the fact that this was the largest deregulatory effort in the history of the country. Right along with that—and they didn’t acknowledge this—it’s the most devastating decision by the federal government endangering public health and welfare in the history of the country.

Here are some of the statistics: Eighteen billion tons of pollution will be in the air we breathe and in the atmosphere [by 2055], driving climate change as a result of this decision, if it holds. Fifty-eight thousand additional deaths will occur as a result of this, and those deaths will come from the effects of climate change, like heat waves, floods, fires, drought—but there are also lots of other kinds of illnesses, respiratory illnesses. There will be 37 million more asthma attacks on Americans as a result of this decision.

Those are some of the health effects, but the impacts go well beyond that. They’re going to increase fuel prices by an estimated 25 cents per gallon by 2035, if this holds. That can result in $1.7 trillion impacts on consumers. Again, Trump was bragging about the fact that this decision saves $1 trillion, but that’s just the cost of compliance for industry. It ignores the cost of climate change.

DOERING: Walk us through what the Trump administration EPA has argued in this move to revoke the engagement finding. How are they framing this?

PARENTEAU: They basically are saying the Supreme Court got it wrong in Massachusetts v. EPA. What Zeldin is saying is, when I read the Clean Air Act, I don’t see in it the authority, the clear delegation of authority to do what the Obama administration did and what the Biden administration did. It’s pretty clear the strategy here is to get this case back to the Supreme Court and have it overrule Massachusetts v. EPA and adopt the reading of the statute that Zeldin is arguing instead. And that would have very profound consequences.

DOERING: In the original proposed rule to revoke the endangerment finding, the Trump EPA seemed to be focusing a little bit on climate denial, on denying the science itself, but I understand that they have really walked that back in this more final rule. What about that aspect?

PARENTEAU: They’re basically saying science doesn’t matter because we don’t have the legal authority to do anything about it. It’s, ’Well, it’s too bad if in fact the science is accurate, because we can’t do anything about it.’ So they have totally shifted the focus. Zeldin has, wisely, I would say, decided [he’s] not going to attack the science, which is rock solid. You’re not denying there’s a danger, you’re saying you can’t do anything about it. That’s what he’s doing.

DOERING: How solid are the legal grounds of this action by EPA? To what extent can they simply rescind this landmark finding in a single action?

PARENTEAU: They can’t do it by themselves.

I’ve worked up three scenarios. There are lots of different ways this could go. The first scenario is, it’s not clear that this case can even get to the Supreme Court before the clock runs out on the Trump administration. He’s got less than three years to go. This case will be ripe for litigation. It goes to the United States Court of Appeals for the District of Columbia, what we call the DC Circuit. It’s a very expert court. It’s also a court that isn’t dominated by conservatives. So the question is, can Trump and Zeldin manage to get through the DC Circuit and up to the Supreme Court before they turn into a pumpkin at the end of their term? I think there’s a 50/50 chance it won’t get there in time.

The reason that’s significant is because if the next president, who we can only hope to God shows more of an understanding of the threat of climate change and more of a commitment to do something about it, they could repeal the repeal and reinstate the endangerment finding. You see the incredible significance of the clock right now. If Trump can’t get this to the Supreme Court and win before he’s done, the next president can erase all of this.

DOERING: What’s the second scenario?

PARENTEAU: The second scenario is Trump does get the thing to the Supreme Court before he’s done, but he loses 5-4, the same way George W. Bush lost 5-4 in Massachusetts v. EPA.

This is a head-count exercise. You start with the three so-called liberal justices. It’s pretty clear you do have their votes to uphold Massachusetts v. EPA. The Trump administration is counting on Chief Justice Roberts being in their corner, but the chief justice has said he thinks Massachusetts v. EPA is settled law, so you don’t have his vote going in.

You know you’re going to get Justice Thomas, Justice Alito and probably Justice Gorsuch. You’re probably going to get Justice Kavanaugh, because Kavanaugh has been very critical of EPA regulation under the Clean Air Act in the past. So there’s four votes.

Where does the fifth vote come from? It comes down to Justice Barrett. She’s the swing vote in this case, if it gets there, and I think from a decision that she rendered in a very important Clean Water Act case, she’s going to have trouble seeing that if the science says this is a danger, if the Supreme Court, 19 years ago, said that EPA had the authority to regulate it, I don’t think she’s going to say, overrule it. That’s why I think there’s a 60-40 chance if it gets to the Supreme Court in time, Trump loses.

DOERING: And the third scenario?

PARENTEAU: The third scenario is Trump wins in the Supreme Court—God forbid, in my view, but I have to acknowledge that’s definitely a possibility.

If that happens, then a future president can’t do anything about it. That’s the significance. Once the Supreme Court has ruled, EPA no longer has the authority to regulate greenhouse gases. Only Congress can reinstate that authority. A future president is hamstrung.

DOERING: Just to clarify, has the endangerment finding actually been revoked by this action by EPA, or does that not happen until the legal battles have been settled?

PARENTEAU: Technically, here’s what happens: The rule is published in the Federal Register, and then 60 days later, the repeal of the tailpipe standards takes effect. So we’re still in a two-month window right now, but when that takes effect, it’s automatic.

Here’s what I predict is going to happen in response to that. The attorneys general of California and Massachusetts have already announced, no surprise, they’re going to challenge this, and I predict that the first thing they’re going to do in the Court of Appeals for the District of Columbia is to move for what we call a stay of the rule, which means put a pause on the rule while the case works its way out. I think they have a very strong case to do that.

This decision overturns again 19 years of regulation. It proposes to overturn a Supreme Court decision that’s already on the books. I think the District of Columbia court is going to say a stay of this rule is entirely appropriate. That’s a long-winded answer, but it means that the rule will take effect unless the D.C. Circuit puts a stay on it.

DOERING: It sounds like this is really just the beginning of the process of repealing this finding.

PARENTEAU: I would say so, and that’s why I say I think it’s going to take longer than three years to sort it out.