MARRAKECH, Morocco -- The election of a U.S. president who has called global warming a “hoax” alarmed environmentalists and climate scientists Wednesday and raised questions about whether America, once again, would pull out of an international climate deal.

Many said it’s now up to the rest of the world to lead efforts to rein in greenhouse gas emissions, while others held out hope that Donald Trump would change his stance and honor U.S. commitments under last year’s landmark Paris Agreement.

“Now that the election campaign has passed and the realities of leadership settle in, I expect he will realize that climate change is a threat to his people and to whole countries which share seas with the U.S., including my own,” said Marshall Islands President Hilda Heine.

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Small island nations which fear they will be swallowed by rising seas are among the biggest supporters of the Paris deal and other international efforts to curb emissions, mainly from fossil fuels.

More than 100 countries, including the U.S., have formally joined the agreement, which seeks to reduce emissions and help vulnerable countries adapt to rising seas, intensifying heat waves, the spreading of deserts and other climate changes.

“I’m sure that the rest of the world will continue to work on it,” Moroccan chief negotiator Aziz Mekouar said at U.N. climate talks in Marrakech.

Many environmentalists and scientists weren’t so sure.

“The Paris Agreement and any U.S. leadership in international climate progress is dead,” said Dana Fisher, director of the Program for Society and the Environment at the University of Maryland. However, the transition toward cleaner energy is so entrenched in the U.S. it would continue without federal money, she added.

The U.S. under the Bush administration declined to join the previous climate deal, the 1997 Kyoto Protocol, which greatly reduced its impact on global emissions. But President Barack Obama made climate change a priority and was instrumental in making the Paris Agreement come together.

Trump pledged in May to “cancel” the Paris deal.

In a signal of how he plans to approach the issue as president, Trump has selected a skeptic of climate change to lead his Environmental Protection Agency transition team.

Myron Ebell of the Competitive Enterprise Institute’s (CEI) is also viewed by many as a top candidate to become the next head of the EPA. Ebell’s research focuses on questioning what he calls “global warming alarmism” and opposing energy rationing policies, according to his biography on CEI’s website.

On the campaign trail, Trump called for stripping regulations to allow unfettered production of fossil fuels — a key source of emissions — and rescinding the Clean Power Plan, an Obama administration strategy to fight climate change.

In May, Trump told an oil and gas conference in North Dakota he would “save the coal industry” and stop all payments of U.S. tax dollars to global warming programs.

“Trump will try and slam the brakes on climate action, which means we need to throw all of our weight on the accelerator,” said May Boeve, leader of the 350.org environmental group.

The pro-fossil fuels American Energy Alliance said Trump’s victory presents a chance to reset “harmful energy policies” in the United States.

“He has laid out an energy plan that puts the needs of American families and workers first,” the group’s president, Thomas Pyle, said.

While shell-shocked American climate activists in Marrakech cried and embraced, U.S. negotiators declined to speak to reporters about the election’s outcome.

However, before the two-week conference, U.S. officials said they expect other countries to stay the course irrespective of what Washington decides, because they see it is in their national interests.

Li Shuo, a climate policy expert at Greenpeace in China, said his nation — the world’s top polluter — would continue to work on climate change “out of its own very genuine concern on air pollution, water pollution and food security.”

The withdrawal process would take four years — an entire presidential term — under the terms of the agreement. However, Trump could also decide to simply ignore the Obama administration’s Paris pledge to reduce U.S. emissions by 26-28 percent from 2005 levels by 2025. The pledges are self-determined, and there is no punishment for countries that miss their targets.

Alden Meyer of the Union of Concerned Scientists, a veteran U.S. observer of the climate talks, said he hopes Trump will adopt a more “responsible” view in office.

“Even he does not have the power to amend and change the laws of physics, to stop the impacts of climate change, to stop the rising sea levels,” Meyer said.

Several analyses have shown that the world is not on track to keep the global temperature rise below 2 degrees C (3.6 degrees F) compared with preindustrial times, the goal of the Paris Agreement. Temperatures have already gone up by half that amount.

Many climate scientists who feel countries aren’t doing enough to reduce emissions were dismayed by the Trump’s victory.

“Can the world do climate stewardship without the U.S.? It has to,” said Jason Box, a glacier expert at the Geological Survey of Denmark and Greenland.

Among the minority of researchers who disagree that global warming is a major threat, Trump’s win sparked hopes that a new administration would somehow change the way science looks at the issue.

“Expect some long-awaited, rigorous examination of the theory/models,” John Christy, of the University of Alabama, Huntsville, wrote in an email. “The danger just isn’t there.”