Chinese President Xi Jinping (center) shakes hands with President Obama and U.N. Secretary General Ban Ki-moon during a joint ratification of the Paris climate change agreement in Hangzhou, China, on September 3, 2016. (Pool/Reuters)

He called global warming a Chinese conspiracy and suggested a “big fat dose” of it might make frosty days more pleasant. Now the pending arrival of a climate denier to the White House has left scientists and treaty backers around the globe scrambling to reassess the path ahead to save the Earth.

Trump’s rise, they fear, will elevate to the highest halls of power a school of thought considered largely fringe in most other corners of the globe: that human activity may not be behind the planet’s warming. Following his surprise victory, a cloud of anxiety has settled over international observers and negotiators meeting at a United Nations conference in Morocco — where they are trying to hash out details of the Paris Agreement struck last year in which over 190 countries including the United States agreed to cut carbon emissions.

Global leaders see the deal as key to combating potentially planet-ruining impacts, including rising seas that submerge coastal cities or fierce changes in weather patterns that could threaten global food supplies. But Trump has vowed to back out of the treaty — as well as to nix other green initiatives pushed by President Obama.

The center of the U.S. pledge is an ambitious promise to reduce the country’s greenhouse-gas emissions by 26 to 28 percent below 2005 levels by 2025. Not only has Trump threatened to step back from the Paris Agreement and the domestic Clean Power Plan, which would drive much of those reductions, but he also wants to fire up domestic coal, oil and gas industries in a manner that might trigger an emissions increase.

That prospect is setting off alarm bells among officials and climate-change experts from Beijing to Berlin.

“I think he will be able to delay implementation in the U.S. if he chooses, and I think the rest of the world has to make a decision whether it will slow down or speed up because of this,” said Christoph Bals, policy director at Germanwatch and an observer at the U.N. conference in Morocco. “This will be the debate we will have in the next couple of months. I hope that most countries will decide to move on, because there are very serious consequences.”

As with other of his most polarizing campaign pledges, it remains unclear whether Trump will follow through with his threat. But his selection of Myron Ebell, a well-known climate contrarian, to lead his Environmental Protection Agency transition team suggests Trump may mean business. So far, individuals close to or orchestrating Trump’s energy and climate policy appear to have close ties to the fossil-fuel industry and climate-skeptic movement.

A U.S. withdrawal from the treaty, some argue, eventually could lead other reluctant nations, particularly in the developing world, to rethink their commitments. That would be especially true if the United States backs out of a part of the plan involving financial aid to help poorer countries make the transition to cleaner fuels and adapt to climate change.

“Many developing-country pledges are conditional on financial support, and if the U.S. refuses to provide its fair share of the funding, the financial resources needed for developing countries to reduce their emissions will not materialize, and many conditional pledges will not be realized,” said Robert Watson, a prominent climate scientist at the University of East Anglia who previously chaired the United Nations’ Intergovernmental Panel on Climate Change and who called a Trump presidency a “potential disaster” for the climate.

One country where the United States’ stance, if it retreats from the Paris process, could cause difficulties is India, which is quickly hurtling toward becoming a global energy giant like China.

Andrew Light, the former senior climate negotiator at the State Department who led bilateral engagement with India before the Paris meeting and is now a professor at George Mason University, said India is unlikely to pull back from its ongoing domestic energy revamp regardless of what Trump does. But a U.S. pullout could complicate talks by reopening already settled debates, such as how much of the burden developed nations should shoulder.

India might “revert back to a claim that developed countries caused this problem in the first place and they’re the ones who should solve it,” Light said.

From Morocco, Alden Meyer, director of strategy for the Union of Concerned Scientists, described a new sense of unease at the U.N. conference. But so far, no nation has indicated its will to walk away if the United States does so, he said.

If Trump takes a divergent path, however, remaining nations would quickly need to redraft plans to limit the damage. A pullout, he warned, also could flood into other areas of global diplomacy, leaving Washington with a diminished voice on security, trade and other issues.

“Frankly,” he said, the other countries at the Morocco conference “think the U.S. would be somewhat stupid to be not engaged in this process.”

Several factors may help limit the damage, even if Trump’s America bails. One saving grace, observers said, is China’s increasingly strong commitment to curbing emissions, in part to address a dramatic pollution crisis at home. A week before the U.S. elections, China’s chief negotiator on climate change, Xie Zhenhua, sharply criticized Trump’s position. “I believe a wise political leader should take policy stances that conform with global trends,” he said.

Said Laurence Blandford, director of international policy analysis at the Center for Clean Air Policy, “This is a big opportunity for the Chinese to take leadership and ownership of climate direction, and they may just do that.” If the United States does pull out of the treaty, he said, “progress would continue but perhaps not as fast as before.”

Also helping is that renewable energies such as solar and wind power are becoming dramatically less expensive, to the point where they are competitive with fossil fuels. That means market forces could propel them forward in the United States with or without federal backing.

In addition, Blandford said, international outreach to U.S. states could partially offset the impact of a federal withdrawal from the treaty.

“California is not going to stop what it’s doing on climate change, even if Trump does,” Blandford said.

Yet breaking away from the agreement would be no easy task. It came into legal force shortly before the U.S. election, and once a party has joined it, the agreement’s text states that a nation cannot withdraw for four years. That would seem, on its face, to rule out Trump simply exiting the accord.

However, Trump could guide a response in which the United States withdraws in all but name, pulling the country out of meetings or simply refusing to meet domestic emissions targets. If the Trump administration does not live up to that, the main penalty would be little more than censure and criticism from other countries.

Trump energy adviser Rep. Kevin Cramer (R-N.D.) also has suggested that the Trump administration might submit the agreement to the Senate for ratification — a vote on which would probably fail.

Stephanie Kirchner in Berlin contributed to this report.