UN chief warns new US leader Donald Trump any move to pull out of historic climate deal would be unacceptable.

UN Secretary-General Ban Ki-moon said action on climate change has become “unstoppable” and he expressed hopes that US President-elect Donald Trump will 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 agreement to limit greenhouse gas emissions, Ban said on Tuesday that US companies, states, and cities were all pushing to limit global warming.

“What was once unthinkable has become unstoppable,” he told a news conference on the Paris agreement, reached by governments last year, ratified in record time, and formally adopted by more than 100 nations, including the United States.

Trump has called human-induced climate change a hoax and pledged to cancel the Paris deal.

French President Francois Hollande said inaction would be “disastrous for future generations, and it would be dangerous for peace”.

“The United States, the largest economic power in the world, the second largest greenhouse gas emitter, must respect the commitments it has undertaken,” Hollande said to applause. The agreement was “irreversible”, he added.

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

Donald Trump, climate finance, and ‘catastrophe’

Ban said he hoped that Trump, elected last Tuesday, would drop his view.

“I am sure he will make a quick, wise decision,” Ban said, adding that climate change was having severe impacts from the Arctic to Antarctica.

He noted that this year is on track to be the warmest year since records began in the 19th century.

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

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

He said Trump – as a “very successful business person” – would understand that market forces were already acting to push the world economy towards cleaner energies, away from fossil fuels.

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.