China, the EU and India, which along with the US make up the four biggest emitters of carbon dioxide, have restated their commitment to the 2015 Paris Agreement on climate change.
Top EU official Donald Tusk said at a summit with China that Brussels and Beijing would step up co-operation.
Mr Trump announced the US was leaving for economic reasons, saying the deal would cost American jobs.
Secretary of State Rex Tillerson said the US would still curb emissions.
Amid widespread international condemnation of the US decision, Russian President Vladimir Putin said he would “not judge” Mr Trump.
The Paris agreement commits the US and 194 other countries to keeping rising global temperatures “well below” 2C above pre-industrial levels and “endeavour to limit” them even more, to 1.5C.
The UN World Meteorological Organisation said on Friday that, in the worst scenario, the US pullout could add 0.3C to global temperatures by the end of the century.
What do the EU and China say?
European Council President Donald Tusk said after meeting Chinese Premier Li Keqiang that the two powers took their responsibilities seriously.
“Today, China and Europe have demonstrated solidarity with future generations and responsibility for the whole planet,” he told reporters at a joint news conference.