UN Secretary-General Ban Ki-moon said on Tuesday action on climate change has become ‘unstoppable’, and he expressed hopes 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 by governments last year, ratified in record time and formally adopted by more than 100 nations including the United States.

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.

Ban said that 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 quick, 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 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,’ he said.

Ban said that companies including 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 that 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.