Michael Bloomberg, the billionaire former mayor of New York, says he will write a $US4.5 million ($5.8 million) cheque to cover this year’s US financial commitment to the Paris Climate Agreement.
President Donald Trump last year pulled the United States out of the pact, making it the only country opposed to it.
Mr Bloomberg, in a CBS interview on Sunday, said he hopes by next year Mr Trump will have changed his mind.
He said he will continue to provide money for the pact if the US does not rejoin the agreement, according to a news release from Bloomberg Philanthropies, the charity he founded.
“Our foundation will uphold our promise to cover any cuts to UN climate funding by the federal government,” Mr Bloomberg said in the statement.
Mr Trump announced on June 1 last year that he would withdraw the US from the Paris climate agreement, but also left the door open to negotiate a better deal for US businesses and workers.
“We are getting out, but we will start to negotiate and we will see if we can make a deal that’s fair,” he said at the time.
Trump’s decision only began the process of withdrawing, a move that will not be completed until 2020.
The US President was not among more than 100 world leaders invited to Paris for a climate summit in December.
The Trump administration has rolled back a number of environmental regulations since he took office.