With the world watching nervously, the feuding among the president’s aides further exposed the fault lines of a chaotic decision-making process that has swirled around Mr. Trump since he took office.
Signs have been increasing for weeks that Mr. Trump was heading toward pulling out of the Paris agreement, apparently believing that a continued United States presence in the accord would harm the economy; hinder job creation in regions like Appalachia and the West, where his most ardent supporters live; and undermine his “America first” message.
At home, he faced urgent pleas from corporate leaders, including Tim Cook, the chief executive of Apple, who told Mr. Trump on Tuesday that pulling out was wrong for business, the economy and the environment. Elon Musk, the chief executive of Tesla, threatened to resign from two White House advisory boards if the president withdrew from the Paris agreement.
In Europe last week, Mr. Trump waved aside a barrage of private lobbying by other heads of state to keep the United States in the agreement.
A frustrated Jean-Claude Juncker, the president of the European Union, said he opposed “behaving as vassals of the Americans” and assailed Mr. Trump for failing to even understand the mechanics of a withdrawal, which he said could take three or four years to fulfill.
“This notion — ‘I am Trump. I am American. America first, so I’m going to get out of it.’ — that is not going to happen,” Mr. Juncker said. “We tried to make that clear to Mr. Trump in clear, German principle clauses in Taormina, but it would appear that he did not understand.”
He added, “Not everything in international agreements is fake news.”
Mr. Trump has shown a willingness to shift direction up until the moment of a public announcement. He met on Wednesday with Secretary of State Rex W. Tillerson, who has advocated that the United States remain a part of the Paris accord. Other advisers pressing Mr. Trump to remain were furiously making their case.
In the past, such appeals have worked. In April, Mr. Trump was set to announce a withdrawal from the North American Free Trade Agreement, but at the last minute changed his mind after intense discussions with advisers and calls from the leaders of Canada and Mexico. Last week, a senior administration official said Mr. Trump would use a speech in Brussels to explicitly endorse NATO’s Article 5 mutual defense provision, which states that an attack on one NATO member is an attack on all. He did not.
The exit of the United States, the world’s largest economy and second-largest greenhouse gas polluter, would not dissolve the 195-nation pact, which was legally ratified last year, but it could set off a cascade of events that would have profound effects on the planet. Other countries that reluctantly joined the agreement could now withdraw or soften their commitments to cutting planet-warming pollution.
“The actions of the United States are bound to have a ripple effect in other emerging economies that are just getting serious about climate change, such as India, the Philippines, Malaysia and Indonesia,” said Michael Oppenheimer, a professor of geosciences and international affairs at Princeton, and a member of the Intergovernmental Panel on Climate Change, a United Nations group that produces scientific reports aimed at informing global policy makers.
Once the fallout settles, he added, “it is now far more likely that we will breach the danger limit of 3.6 degrees” — the average atmospheric temperature increase above which a future of extreme conditions is considered irrevocable.
The aim of the Paris agreement was to lower planet-warming emissions enough to avoid that threshold.
“We will see more extreme heat, damaging storms, coastal flooding and risks to food security,” Professor Oppenheimer said. “And that’s not the kind of world we want to live in.”
Foreign policy experts said the move could damage the United States’ credibility and weaken Mr. Trump’s efforts to negotiate issues far beyond climate change, like trade and terrorism.
“From a foreign policy perspective, it’s a colossal mistake — an abdication of American leadership,” said R. Nicholas Burns, a retired career diplomat and an under secretary of state for President George W. Bush.
“The success of our foreign policy — in trade, military, any other kind of negotiation — depends on our credibility,” Mr. Burns said. “I can’t think of anything more destructive to our credibility than this.”
But Mr. Trump’s supporters, particularly coal-state Republicans, have cheered the move, celebrating it as a fulfillment of a signature campaign promise. Speaking to a crowd of oil rig workers last May, Mr. Trump vowed to “cancel” the agreement, and Stephen K. Bannon, Mr. Trump’s chief strategist, has pushed the president to withdraw from the accord as part of an economic nationalism that has so far included pulling out of the Trans-Pacific Partnership, a multilateral trade pact, and vowing to renegotiate the North American Free Trade Agreement.
Coal miners and coal company executives in states such as Kentucky and West Virginia have pushed for Mr. Trump to reverse all of President Barack Obama’s climate change policies, many of which are aimed at reducing the use of coal, considered the largest contributor to climate change.
In a May 23 letter to Mr. Trump from Attorney General Patrick Morrisey of West Virginia and nine other state attorneys general, Mr. Morrisey wrote, “Withdrawing from the Paris agreement is an important and necessary step toward reversing the harmful energy policies and unlawful overreach of the Obama era.” He added, “The Paris agreement is a symbol of the Obama administration’s ‘Washington knows best’ approach to governing.”
Although the administration has been debating its position on the Paris agreement for months, the sentiment for leaving appears to have the upper hand over the views of Mr. Tillerson and Ivanka Trump, the president’s daughter and close adviser.
Other countries have vowed to continue to carry out the terms of the Paris agreement, even without the United States.
President Xi Jinping of China, the world’s largest greenhouse gas polluter, has promised that his country will move ahead with steps to curb climate change, regardless of what happens in the United States.
During a telephone call in early May with President Emmanuel Macron of France, according to the Chinese Foreign Ministry, Mr. Xi told the newly elected French leader that China and France “should protect the achievements of global governance, including the Paris agreement.”
But the accord’s architects say the absence of the United States will inevitably weaken its chances of being enforced. For example, the United States has played a central role in pushing provisions that require robust and transparent oversight of how emissions are monitored, verified and reported.
Without the United States, there is likely to be far less pressure on major polluting countries and industries to accurately report their emissions. There have been major questions raised about the accuracy of China’s emissions reporting, in particular.
“We need to know: What are your emissions? Where are your emissions?” said Todd D. Stern, the lead climate negotiator during the Obama administration. “There needs to be transparent reporting on countries’ greenhouse gas emissions. If the U.S. is not part of that negotiation, that’s a loss for the world.”