The global fight against climate change will suffer a blow from Donald Trump’s victory in the U.S. presidential election, threatening the industries working to clean up pollution from fossil fuel.

The next president has questioned the science of climate change, vowed to withdraw from the Paris agreement on global warming and pledged to stimulate production of coal, the dirtiest fossil fuel. Green campaigners and policymakers, some of whom are gathered this week in Morocco for talks on implementing the Paris deal, sounded the alarm over the upheaval they expect when Trump takes office in January.

“The presidency of Donald Trump relegates the West as we knew it to the realm of the past,” Reinhard Butikofer and Monica Frassoni, co-chairs of the European Green Party, said in a statement. “If Donald Trump pursues the foreign policies that he announced during his campaign, this will severely undermine trans-Atlantic relations, the international rule of law and world peace.”

Under President Barack Obama, the U.S. rescued a two-decade-old process the United Nations promoted to rein in pollution damaging the climate, forging the Paris deal last year. Along with China and more than 190 other countries, the accord set out a framework for all nations to cut emissions. Trump has said he will cancel that work.

“This is a very bad outcome,” Tom Steyer, founder of San Francisco-based advocacy group NextGen Climate Action, said in a phone interview Wednesday. “The Paris accord was a historic attempt to move forward as a globe to deal with a global problem, with American leadership. If he follows through on his campaign statements, that would be a devastating mistake.”