Tusk warned Trump on Twitter against such a move as he prepared to host an EU-China summit on Friday.
Tusk warned Trump on Twitter against such a move as he prepared to host an EU-China summit Friday designed to fill the void on climate if the US withdraws from the landmark 2015 pact.
"@realDonaldTrump please don't change the (political) climate for the worse," Tusk said after Trump tweeted he would make his final decision at 1900 GMT.
Tusk will join Jean-Claude Juncker, president of the executive European Commission, in meeting Chinese Prime Minister Li Keqiang at the summit on Friday.
Li pledged to "steadfastly" implement the Paris pact as he held talks with German Chancellor Angela Merkel before travelling later Thursday to Brussels for informal talks.
The European Union and Chinese leaders will throw their full weight behind implementing all aspects of the Paris agreement, regardless of US participation, according to a draft statement expected to be published Friday.
The United States is the world's second biggest carbon emitter, after China.
The US administration under Trump -- who once called climate change a Chinese "hoax" -- has resisted intense pressure from US partners to respect the global accord.
America's international allies and Trump's domestic opponents lashed out Wednesday at media reports that he had made up his mind to pull Washington out of the agreement to curb carbon emissions.
Trump said he'd been "hearing from a lot of people, both ways. Both ways."
The summit in Brussels could mark a dramatic shift in global politics, with the EU taking over from the United States in working with China to fight climate change.