Here's what his ambassador to the United Nations says: "President Trump believes the climate is changing".
As President Trump pulls out of an accord crafted in Paris, New York's former mayor landed there with a message to a jolted world.
It even drew criticism from some Republicans, as small demonstrations erupted in NY and Washington.
Over the last decade, the USA military and intelligence officials have developed a broad agreement about the security threats that climate change presents, in part by threatening to cause natural disasters in densely populated coastal areas, damage American military bases worldwide and open up new natural resources to global competition. "Americans will honor and fulfill the Paris Agreement by leading from the bottom up - and there isn't anything Washington can do to stop us", Bloomberg said.
According to Brown's office, California has the sixth largest economy in the world and California, New York and Washington together represent about 68 million people - almost one-in-five Americans - and at least 10 percent of greenhouse gas emissions in the United States.
Mexican ministers said the world had a "moral imperative" to live up to the Paris commitments, while Brazil's foreign ministry said it was concerned and disappointed by Washington's move. "He knows that the USA has to be responsible with it, and that's what we're going to do".
"We have used that island for every significant military operation in Southwest Asia", said Titley, who now teaches at Pennsylvania State University.
The former NY mayor said work would continue to reduce emissions.
"We will now start the process of increasing our goals to lower emissions even further and faster, because bluntly. we're going to have to shoulder more of the burden now", he said.
"It would be a way of telling not just the United Nations, but cities and other regions around the world, this is what New York City or New York State plan to do", Gundlach said.
"What's really happening here is the president may have unwittingly added dynamism to the same actors that have always been the ones that are delivering the reductions to actually do more on their own", he told AFP.
California, New York and Washington, which have formed their own alliance, represent more than one-fifth of USA gross domestic product and account for at least 10 per cent of greenhouse gas emissions in the United States, their governors said.
They are hoping more governors will join them.
Reacting to USA decision, PM Modi, who is in Russian Federation for the St Petersburg International Economic Forum, said, "Paris or no Paris, our commitment to preserving the climate is for the sake of future generations".
The United Nations said America's exit from Paris was a "major disappointment", with a spokesman for Secretary-General Antonio Guterres urging the U.S. to remain a "leader on environmental issues".