Former New York Mayor Michael Bloomberg says he will pay $ 4.5 million (£ 3.2 million) to cover the US past financial commitment to the Paris Climate Agreement.
He said he was due to the president's responsibility to improve the environment Donald Trump's decision to withdraw from the deal.
The withdrawal was announced in June last year, triggering international condemnation.
It will make the US virtually the only country that is not part of the Paris Agreement.
The Paris Agreement commits the US and 1
"America is committed and, as an American, if the government does not, then we all have a responsibility," Bloomberg said on CBS.
"I can do that. So, yes, I'll send them a check on the funds that America has promised the organization, as if they had it from the federal government."
His charity offered Bloomber g philanthropies $ 15 million to cover a separate shortage of climate change over the past year.
It said the money would go to the United Nations Framework Convention on Climate Change (UNFCCC).
In January, President Trump said the US could be "imaginable" if it treated America more equitably.
"It's an agreement that I have no problem, but I had a problem with the agreement they signed (the Obama administration)," he told reporters.  Mr Bloomberg said he hopes Mr. Trump will reconsider his position on the deal by next year.
"It is known that he changes his mind, that's true," he said. "America is a big part of the solution and we should go in and help the world stop a potential disaster."
What is in the Paris Climate Agreement?
The agreement brings together all the nations of the world in a single agreement on climate change for the first time in history
A consensus among nearly 200 countries on the need to reduce greenhouse gas emissions is seen by many observers as an achievement and referred to as "historical".  In addition to limiting global temperatures, it includes limiting the amount of greenhouse gases emitted by human activities and requiring rich nations to help poorer nations through "climate finance."