MARRAKESH, Morocco — UN Secretary-General Ban Ki-moon said on Tuesday action on climate change has become “unstoppable” and predicted that US President-elect Donald Trump would drop plans to quit a global accord aimed at weaning the world off fossil fuels.

At a meeting of almost 200 nations in Morocco to work out ways to implement the 2015 Paris agreement to limit greenhouse gas emissions, Ban said US companies, states and cities were all pushing to limit global warming.

“What was once unthinkable has become unstoppable,” he told a news conference of the Paris Agreement, agreed to by governments last year, and which formally entered into force on Nov. 4 after a record quick ratification.

Ban said Trump, as a “very successful businessperson,” would understand that market forces were already driving the world economy toward cleaner energies such as wind and solar power, as they become cheaper, and away from fossil fuels.

The Paris accord, aiming to phase out net greenhouse gas emissions this century, was a breakthrough after more than two decades of deadlock, driven by increased scientific certainty that man-made emissions drive heat waves, floods and rising sea levels.

Ban said he hoped that Republican Trump, elected last Tuesday, would drop his view that man-made climate change is a hoax and his pledge to cancel the Paris Agreement.

“I am sure he will make a … wise decision,” Ban said, saying that climate change was having severe impacts from the Arctic to Antarctica. He noted this year is on track to be the warmest since records began in the 19th century.

“I hope he will really hear and understand the seriousness and urgency of addressing climate change. As president of the United States I hope he understands this, listens and evaluates his campaign remarks,” he said.

Ban said that companies including General Mills and Kellogg, states such as California and cities such as Nashville and Las Vegas were working to cut their greenhouse gas emissions.

Ban, who will step down at the end of the year after a decade in charge of the United Nations, has made action on climate change a core issue of his time in office.

Trump’s victory has overshadowed the Nov. 7-18 Marrakesh meeting, which had opened with congratulations after the entry into force of the agreement on Nov. 4. It now has formal backing from 110 nations including the United States.

Trump has said he will boost the US coal, oil and shale industries, abandoning President Barack Obama’s plan to cut greenhouse gas emissions by 26 to 28 percent below 2005 levels by 2025.

His victory has lifted shares in coal producers, while knocking renewable energies.

Shares in coal producer Peabody, in bankruptcy proceedings, have surged 63 percent since the election, and shares in Arch Coal in the United States were up 19 percent.

By contrast, the S&P Global Clean Energy Index has fallen to around its lowest level since June. Shares in Denmark’s Vestas, the world’s biggest wind turbine maker, are down 6 percent from the US election day on Nov. 8.

A source on his transition team said Trump is seeking ways of withdrawing from a global agreement to limit climate change within a year, bypassing a theoretical four-year wait.

But nations as diverse as China, Saudi Arabia and small island states at risk from rising sea levels have reaffirmed support for the Paris Agreement since Trump’s victory and expressed hopes that Trump will change track once in office.

A US withdrawal could dent other nations’ willingness to work with Trump on other issues he cares about, such as immigration, trade or terrorism.

“Climate change has moved from a silo issue to a core issue of diplomacy. Others will continue to see it this way,” said David Waskow, of the Washington-based World Resources Institute think tank.

He said a Trump withdrawal would also cast doubt over Washington’s role in other international groups, such as the Group of Seven or the Group of 20, where global warming is often a topic.

Even major oil companies are pledging to act.

On Nov. 4, some of the world’s biggest oil companies, including Saudi Aramco and Royal Dutch Shell, pledged to invest $1 billion to develop climate-friendly technologies under the Paris Agreement.