British billionaire Richard Branson on Thursday called President Donald Trump very "naive" to withdraw from the Paris climate accord, saying he failed to recognize that clean energy is cheaper than coal and oil and is going to create "massively more jobs."

The business magnate, climate activist and philanthropist also questioned Trump's decision to put "America First" since there are no barriers when it comes to climate and water in the oceans.

Speaking on World Oceans Day, Branson said many supporters of the Paris agreement "cried" when Trump announced that the United States will pull out of the Paris agreement to limit carbon emissions that are warming the planet.

"We wanted the United States of America to not talk selfishly but to talk about being part of this world which doesn't have walls, and help us get out there and save it," he said.

The founder and head of the Virgin Group belongs to a group of global leaders called OceanElders that promotes the protection of the world's seas. He spoke at a press event and in an interview later with The Associated Press on the sidelines of the first U.N. conference on oceans.

Branson said he's optimistic that the momentum from the conference will lead to sustained action to meet U.N. goals of cleaning up the oceans and ending overfishing by 2030.

"There are 10,000 people here who want to make a difference, and they want to see species in the oceans protected as much as the species in Africa and other places," he said. "I really think we can do it."

Branson said there are also a lot of world leaders that want to leave legacies when they step down and "if they can leave a big marine reserve, or something in their name, that's very positive." Former U.S. presidents Barack Obama and George W. Bush established marine reserves, and so did former British Prime Minister David Cameron, he said.

Branson cited last October's historic agreement by 24 countries and the European Union to create the world's largest marine protected area in the Ross Sea next to Antarctica. The U.S., Russia and China are part of the agreement which covers an area about twice the size of Texas.

Branson said "our big worry at the moment is whether Trump will try to reverse it."

He said the U.S. leader has asked to look at possibly reversing agreements on some protected areas, "and that would be a disaster."

"We just have to hope he's got other things on his mind right now and he doesn't do that," he said.

If he had the chance to meet Trump, Branson said he would tell the president that they are now both grandfathers. And he would say to him: "History will be kind to us if we do something for our grandchildren, and history will not forgive us if we neglect our grandchildren."

"Neglecting them would mean not looking after the environment, not looking after the oceans, not looking after the species on earth, and being selfish," Branson said.