"America made a commitment and, as an American, if the government's not going to do it, we all have responsibility", he told CBS's "Face the Nation".
The former NY mayor and philanthropist's pledge fills a "significant funding gap" that follows US President Donald Trump's intention to withdraw from the Paris Agreement and proposed budget cuts for worldwide programmes, including climate projects.
Asked if he thought the nonbinding nature of the Paris deal was a problem, in terms of other countries not sticking to its aims for reducing greenhouse gas emissions and other targets aimed at reducing the effect of climate change, Bloomberg said: "Look, it's risky to keep doing what we're doing".
As part of the agreement, the U.S. had pledged $3bn to the Green Climate Fund, set up by the United Nations to help countries deal with the effects of global warming.
"Our foundation will uphold our promise to cover any cuts to United Nations climate funding by the federal government - and the American people will uphold our end of the Paris Agreement, with or without Washington", Bloomberg said in a statement. "Therefore, sure, I'm going to send them a check for those monies that America had promised into the company like they got it from the national government".
Even though the treaty is non-binding and some countries have not lived up to its terms, Bloomberg said that if some countries were doing their part, it was still a good deal.
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"He should change his mind [on the Paris climate agreement] and say look there really is a problem here", said Bloomberg.
"He's been known to change his mind, that is true", he said. He said Trump should understand that America is part of the problem as well as the solution and should chip in and help the planet avert a disaster.
In January, Trump said the USA could "conceivably" return to the deal if it treated America more fairly.
The money is used to fund the UN's work in supporting developing countries adapt to the impacts of climate change; promote climate action across society, and address institutional needs in areas such as IT and communications.
Trump staunchly opposes the agreement and his administration has rolled back a number of environmental regulations.
"That's not his job", Bloomberg said. That to debunk science and walk away from it is just ridiculous.