The man who claimed that global warming and climate change is a hoax perpetrated by the Chinese will be president in a few months, and that’s extremely bad news for environmental activists. Donald Trump has promised to cancel the historic Paris Agreement, which put in place numerous goals for the world’s nations to reduce carbon emissions and therefore keep the temperature of the Earth from continuing to rise.

With Trump’s election, world leaders are beginning to fear that the effort to deal with global warming could be hobbled, or even derailed all together, as without the United States’ participation, the effort would be futile.

“I hope that his rhetoric doesn’t match his actions,” senior climate change specialist Rasmus Lauridsen, at European Investment Bank, told CNN. “I’ve read an analysis saying that people take what he says seriously, but not him seriously. Maybe we should do the opposite and disregard what he says.”

Trump has attacked the Clean Power Plan, something that President Obama championed to change the energy industry in the United States. Critics of the plan call it a “war on coal,” and it will go before the Supreme Court next year.

“The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive,” Trump tweeted back on Nov. 6, 2012.

He later claimed he had never said so during a debate with Clinton, and yet he never bothered to delete the tweet to cover his tracks. Later, he called the tweet a “joke.”