Trump, who has labeled climate change a "hoax," made good on a campaign promise to "cancel" the Paris agreement and Obama-era regulations that he said were decimating industries and killing jobs. The president cast his decision as a "reassertion of America's sovereignty," arguing that the climate pact as negotiated under President Barack Obama was grossly unfair to the U.S. workers he had vowed to protect with his populist "America First" platform.
"I was elected to represent the citizens of Pittsburgh, not Paris," Trump proclaimed in a forceful, lengthy and at times rambling speech from the Rose Garden of the White House. He added, "As of today, the United States will cease all implementation of the nonbinding Paris accord and the draconian financial and economic burdens the agreement imposes on our country."
The United States joins only two countries — Nicaragua and Syria — in opposing a climate agreement reached by all other nations in 2015. A signature diplomatic achievement for Obama, the Paris accord was celebrated at the time as a universal response to the global warming crisis.
The U.S. withdrawal from the Paris agreement cannot actually be finalized until near the end of Trump's term because of the accord's legal structure and language.
With the world's second-largest emitter of greenhouse gases walking away from the pact, scientists said it would be nearly impossible for the world to realize its agreed goal of limiting global warming to below a 2-degree Celsius (3.6-degree Fahrenheit) rise above preindustrial temperatures.
Still, many U.S. states and private companies announced Thursday that despite Trump's decision, they would continue their own existing policies, such as restricting greenhouse gas emissions, as well as pursue new ones to demonstrate urgency in addressing the climate threat.
Citing a litany of statistics disputed by environmentalists, Trump argued Thursday that the pact would hurt domestic manufacturing and other industries and would put the United States at a "permanent disadvantage" with China, India and other rising powers. Staying in the accord, he said, would cost the United States as many as 2.7 million jobs by 2025 and as much as $3 trillion in lost gross domestic product.
"We're going to have the cleanest air," Trump said. "We're going to have the cleanest water. We will be environmentally friendly. But we're not going to put our businesses out of work. We're not going to lose our jobs."
In a gesture to those who had encouraged him to remain in the accord, Trump said he was open to negotiating a new climate deal that, in his assessment, would be more fair to U.S. interests.
"We're getting out," he added, "but we will start to negotiate and we will see if we can make a deal that's fair. If we can, that's great. And if we can't, that's fine."
The leaders of France, Germany and Italy issued a joint statement voicing "regret" about Trump's move, promising to redouble their efforts to implement the Paris agreement and asserting that it cannot be renegotiated.
"We deem the momentum generated in Paris in December 2015 irreversible and we firmly believe that the Paris Agreement cannot be renegotiated, since it is a vital instrument for our planet, societies and economies," read the statement from French President Emmanuel Macron, German Chancellor Angela Merkel and Italian Prime Minister Paolo Gentiloni.
Trump spoke by phone with Merkel and Macron, as well as Canadian Prime Minister Justin Trudeau and British Prime Minister Theresa May — who led a chorus of world leaders urging Trump to keep the United States in the Paris agreement.
"He is making a mistake for the future of his country and his people and a mistake for the future of the planet," Macron said.
Erik Solheim, executive director of the United Nations Environment Program, said in an interview that "the biggest losers will be the American people."
"It's obviously regrettable," he said. "The world needs American leadership. However, the impact is less than most people would believe, because China, India and Europe will provide leadership."
Central to Trump's rationale was his feeling that the United States had been taken advantage of. Trump argued the Paris accord was so unfavorable to U.S. interests that other countries were laughing at America.
"The rest of the world applauded when we signed the Paris agreement," Trump said. "They went wild. They were so happy. For the simple reason that it put our country, the United States of America, which we all love, at a very, very big economic disadvantage."
The president, who recently returned from his maiden foreign trip, added, "We don't want other leaders and other countries laughing at us anymore — and they won't be."
Obama strongly defended the Paris agreement as a measure to "protect the world we leave to our children." In a statement released Thursday, he said the pact was the product of "steady, principled American leadership on the world stage," pointing out that it had broad support from the private sector.
"I believe the United States of America should be at the front of the pack," Obama said. "But even in the absence of American leadership; even as this administration joins a small handful of nations that reject the future; I'm confident that our states, cities, and businesses will step up and do even more to lead the way, and help protect for future generations the one planet we've got."
A divide in Trump's camp
The atmosphere in the Rose Garden was celebratory, with a military band performing "Summertime" and other jazz hits as Cabinet members, White House staffers, conservative activists and other Trump supporters took their seats in the garden under a bright sun.
The scene was a reflection of the deep divide within the Trump administration over Paris. The president took much of the spring to make up his mind amid an intense campaign by both sides to influence his decision.
Secretary of State Rex Tillerson and Ivanka Trump, the president's daughter and adviser, are among those who urged him to stay in the deal, arguing it would be beneficial to the United States to remain part of negotiations and meetings surrounding the agreement as a matter of leverage and influence. Neither attended Thursday's ceremony.
White House chief strategist Stephen K. Bannon and Environmental Protection Agency Administrator Scott Pruitt pushed for a withdrawal. When Trump announced that he would pull out, there was a burst of applause and some whoops from the assembled crowd in the Rose Garden — and Bannon held his hands up in the air, clapping enthusiastically.
Introducing Trump, Vice President Pence said the climate decision was an example of the president putting what he sees as the interests of the United States above all else.
"Our president is choosing to put American jobs and American consumers first," Pence said. "Our president is choosing to put American energy and American industry first. And by his action today, President Trump is choosing to put the forgotten men and women first."
More than 190 nations agreed to the accord in December 2015 in Paris, and 147 have since formally ratified or otherwise joined it, including the United States — representing more than 80 percent of the world's greenhouse gas emissions.
It's also heavily backed by U.S. and global corporations, including oil giants Royal Dutch Shell, ExxonMobil and BP. Large corporations, especially those operating in international markets, have had years to get used to the idea of reductions on carbon emissions, and they have been adapting their businesses accordingly for some time.
Withdrawing the United States from the agreement could take years because of the accord's legal structure and language, but such a move would weaken its goals almost immediately. The United States is the world's second-largest greenhouse gas emitter and would otherwise have accounted for 21 percent of the total emissions reductions achieved by the accord through 2030.
'Reckless and indefensible'
Condemnations of Trump's decision were immediate and strongly worded. Former vice president Al Gore, who won a Nobel Peace Prize for his work raising awareness about global warming and personally tried to persuade Trump, said the president's decision was "reckless and indefensible."
"It undermines America's standing in the world and threatens to damage humanity's ability to solve the climate crisis in time," Gore said in a statement.
Jeff Immelt, the chief executive of General Electric, tweeted: "Disappointed with today's decision on the Paris Agreement. Climate change is real. Industry must now lead and not depend on government."
Tesla chief executive Elon Musk and Disney chief executive Robert Iger both announced Thursday that they were leaving Trump's business advisory council over his decision to withdraw from the Paris deal.
In Europe, a top German politician slammed Trump's decision, mocking him for his brusque brush-aside of a Balkan leader last week at a NATO meeting in Brussels. "You can withdraw from a climate agreement but not from climate change, Mr. Trump," Social Democratic leader Martin Schulz wrote on Twitter. "Reality isn't just another statesman you shove away."
But on Capitol Hill, Republican leaders praised Trump's move. Senate Majority Leader Mitch McConnell (R-Ky.) said in a statement, "I applaud President Trump and his administration for dealing yet another significant blow to the Obama Administration's assault on domestic energy production and jobs."
House Speaker Paul D. Ryan (R-Wis.) said, "The Paris climate agreement was simply a raw deal for America . . . I commend President Trump for fulfilling his commitment to the American people and withdrawing from this bad deal."
There was some Republican dissent, however. Sen. Susan Collins (R-Maine) tweeted: "Climate change requires a global approach. I'm disappointed in the President's decision."
Brady Dennis, Juliet Eilperin and Chris Mooney in Washington, Michael Birnbaum in Brussels and James McAuley in Paris contributed to this report.