International governments have made a power play against Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE by ratifying an international climate deal earlier than expected, effectively preventing him from “canceling” the deal as he has promised to do.

The European Union’s Tuesday decision to join the Paris climate deal will push the deal over the threshold for ratification; it will formally take effect in 30 days.

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That means Trump, should he be elected president in November, could not “cancel” or renegotiate the terms of the agreement.

President Obama committed the United States to reduce its emissions by 26 percent to 28 percent by 2025 as part of the deal. The agreement is nonbinding, so Trump would be free to ignore it if he wins the White House.

Some say Trump’s rhetoric about the deal helped speed up ratification.

Most officials expected the climate deal, negotiated in December in Paris, to take effect no earlier than next year. A similar international climate accord, the Kyoto Protocol, wasn’t ratified for five years.

But the specter of a Trump presidency appears to have spurred the deal along.

“His threat stimulated this rapid series of ratifications — China, the USA, Europe, and many others,” Robert Stavins, the director of the Harvard Project on Climate Agreements, wrote in an email.

John Coequyt, the global climate policy director at the Sierra Club, said foreign leaders likely moved quickly to join the deal to close off any future debate over the need for international climate action.

“They want to be on the right side of the issue, and I believe that Trump showed the world that that isn’t a foregone conclusion,” Coequyt said, noting a summer study concluding that Trump would be the only head of state in the world to doubt the science behind climate change.

“I think having that idea out there, that the world still is debating this in some way, I think puts pressure on countries to act quickly, to solidify the process and continue to move forward.”

Once the deal takes effect, the United States cannot back out of the plan — or force changes to it — for at least four years.

Trump has opposed the Paris deal since before the United Nations meeting on the matter in December.

Once negotiators struck the agreement, the Republican presidential nominee ramped up his criticism. First he said he would renegotiate the agreement to get a more favorable deal for the United States. Then he told the energy industry in a May speech that he would “cancel” it if he were elected.

International officials pushed back.

In May, Patricia Espinosa, the U.N.’s new climate chief, said it wouldn’t be “feasible” for Trump to change the terms of the pact. And the possibility of a Trump presidency reverberated among international climate negotiators, with Obama’s international climate envoy this spring saying he had to reassure other countries the U.S. could meet its commitments under the deal despite domestic politics.

Before the U.S. joined the agreement in September, Obama’s top climate change adviser, Brian Deese, said the dynamics of a change in presidential administration is “certainly a discussion we have.”

“The history of these agreements is: Once they’re in place and once the United States has not only supported and signed the agreement, but has formally joined the agreement, that we stay in the agreement that we commit to,” Deese told reporters in early September.

“We’re quite confident that the United States will continue to be a part of the agreement going forward.”

Still, Trump could ignore the goals that Obama has set — and some conservatives expect he would do just that.

William Yeatman, a senior fellow at the conservative Competitive Enterprise Institute, said Trump could also insist the Senate needs to ratify the deal and send it to lawmakers, who would likely vote it down.

Environmental groups, though, predict that Trump would find there are limits to how much of the climate push he can stop.

Coequyt predicted world leaders would use diplomacy to pressure countries that don’t join the deal into taking action on climate anyway. Stavins predicted that several environment-related measures, like fuel standards for cars or regional climate efforts, would remain on the books.

“Yes, he could slow down action on climate change, but not as dramatically as he may think he could.”

But Trump would have the power to shape American policy in other ways, including by nominating a ninth justice to the Supreme Court.

The high court is likely to decide the fate of Obama’s biggest climate change regulation, likely in its next term.

If the court struck down the rule, the U.S. might have a hard time meeting its commitments under the Paris deal.

“If you control the presidency, then you can exert a huge amount of power,” Yeatman said. “You can basically not implement your commitments, and you’re not going to suffer anything on the world stage.”