President Donald Trump announced Thursday that his administration will pull the United States out of the Paris agreement on climate change, making the U.S. one of only three countries in the world that aren't part of the landmark international accord.

"In order to fulfill my solemn duty to protect America and its citizens, the United States will withdraw from the Paris climate accord but begin negotiations to reenter either the Paris accord or an entirely new transaction under terms that are fair to the United States," Trump said from the White House Rose Garden. "We're getting out. And we will start to renegotiate and we'll see if there's a better deal. If we can, great. If we can't, that's fine."

Trump noted that "as someone who cares deeply about our environment, I cannot in good conscience support a deal which punishes the United States."

"The Paris accord is very unfair at the highest level to the United States," he said, adding that he was "elected to represent the citizens of Pittsburgh, not Paris."

Prior to the announcement, the White House sent talking points to supporters, saying the deal would kill jobs.

"The Paris Accord is a BAD deal for Americans, and the President's action today is keeping his campaign promise to put American workers first," the talking points read . "The accord was negotiated poorly by the Obama administration and signed out of desperation. It frontloads costs on the American people to the detriment of our economy."

The announcement begins a lengthy withdrawal procedure that won't culminate until November 2020.

In response to Trump's announcement, former President Barack Obama said in a statement that "in the absence of U.S. leadership ... states, cities and business will step up."

"The nations that remain in the Paris Agreement will be the nations that reap the benefits in jobs and industries created," he said.

Trump clashed with global leaders on the future of the Paris accord last week, upsetting German Chancellor Angela Merkel in particular, who had called the climate talks with the president “largely unsatisfying.”

"The Paris deal isn't just any other deal," Merkel told Deutsche Welle . "It is a key agreement that shapes today's globalization."

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Pope Francis had also strongly encouraged Trump to remain in the Paris agreement during their recent meeting. As news reached the Vatican Wednesday that Trump was unlikely to heed the pope's request, Cardinal Peter Turkson, who led a Vatican delegation that was influential in brokering the Paris agreement in 2015, told The Washington Post the news "for us is something we hoped would not have happened."

"Certain issues should be taken out of the political discussion domain and not be politicized," he said. "The truth is, climate is a global public good and not limited to any country."

Trump’s senior adviser Steve Bannon and EPA chief Scott Pruitt had lobbied the president to exit the accord, according to the Washington Post , while Secretary of State Rex Tillerson and Ivanka Trump had urged Trump not to withdraw.

Trump long delayed his decision to pull out of the Paris accord, previously telling the New York Times shortly after the election that he would keep an “open mind” about the agreement , adding that he believed there was "some connectivity" between human activity and rising global temperatures.

However, in the same meeting, he had also noted that he was concerned about "how much it (would) cost our companies” and “its effect on American competitiveness.”

Some analysts say Trump's fears are unfounded.

"Withdrawing from the Paris agreement is hardly going to create jobs in the U.S.," Cary Coglianese, professor at the University of Pennsylvania and editor of the book "Does Regulation Kill Jobs?" told the AP on Thursday. ''While specific environmental regulations can sometimes lead to job losses, they also can and do lead to job gains — with the result being roughly a wash."

Michael Greenstone, an economist at the University of Chicago, said that while "regulations have costs, they are not the primary driver of employment."

A letter signed by 25 major U.S. firms, including Apple, Google, Facebook, Gap, Microsoft and Unilever, ran as a full-page ad in Washington, D.C. newspapers on Thursday urging Trump to remain in the accord, saying it would be better for the economy to do so.

"By expanding markets for innovative clean technologies, the agreement generates jobs and economic growth," the letter says . "U.S. companies are well positioned to lead in these markets."

With the participation of 195 countries, the Paris agreement was reached in December 2015 and officially took effect in November 2016. Nicaragua and Syria were the only countries in the world to reject the agreement. The accord was the first of its kind addressing global warming to be signed, ratified and put into force. Its intent was to keep the planet from rising above pre-industrial averages to two degrees Celsius or 3.6 degrees Fahrenheit by 2100.

The U.S. had agreed under Obama to reduce emissions to 26 percent to 28 percent of 2005 levels by 2025 — about 1.6 billion tons.

The agreement committed rich and poor countries to take action to curb man-made greenhouse gases, which 97 percent of scientists who actively study climate change affirm “is a significant contributing factor in changing mean global temperatures.” Numerous studies published in peer-reviewed journals have also consistently shown rising global temperatures to be tied to human activity.

Scientists warned that withdrawing from the Paris agreement would be “severe and long-lasting for our planet’s climate.”

Researchers say the Earth is likely to reach more dangerous levels of warming even sooner than predicted with the U.S. pull out.

In fact, the decision may result in emissions of up to 3 billion tons of additional carbon dioxide in the air each year. When it adds up year after year, scientists say that is "enough to melt ice sheets faster, raise seas higher and trigger more extreme weather."

"If we lag, the noose tightens," Princeton University climate scientist Michael Oppenheimer, co-editor of the peer-reviewed journal Climatic Change, told the Associated Press.

Last year, 375 top scientists signed an open letter advising Trump against pulling out of the accord.

The scientists said withdrawing would threaten “crossing climatic points of no return, possibly setting in motion large-scale ocean circulation changes, the loss of major ice sheets, and species extinctions.”

The New York Times’s Coral Davenport also noted that while Trump cannot legally stop other nations from carrying through with their Paris agreement commitments, by withdrawing from the accord , he would critically stifle efforts to reduce emissions in the United States. Experts cautioned that this would set the planet on a collision course towards further extreme weather, rising sea levels and dangerous droughts.

Those who urged the Trump administration to pull out of the agreement, including several Republican senators, argued that the agreement opens up the government to diplomatic headaches and possible legal action.

“Under the Paris Agreement, a nation honors its ‘non-binding’ emission reduction and climate finance commitments by turning those promises into enforceable obligations — domestic laws and regulations,” Christopher Horner, a senior fellow at the Competitive Enterprise Institute, wrote in a report published earlier this month. “Thus, the only way to unplug from the pressure machine is to withdraw from the agreement.”

Still, scientists overwhelmingly agree the U.S. exit from the agreement will have significant repercussions.

"Developed nations — particularly the U.S. and Europe — are responsible for the lion's share of past emissions, with China now playing a major role," Rutgers University climate scientist Jennifer Francis, told the AP Wednesday. "This means Americans have caused a large fraction of the warming."

There are, however, some scientists who argue that even if the U.S. had abided by its commitment under the Paris agreement, the world will still pass that 2-degree mark, just at a faster rate, resulting in "ecosystems being out of whack with the climate, trouble farming current crops and increasing shortages of food and water," the National Center for Atmospheric Research's Kevin Trenberth told AP.

John Schellnhuber, director of the Potsdam Institute for Climate Impact Research, who is credited with coming up with the 2-degree goal, says the pull-out might not have a great impact in the end.

"Ten years ago (a U.S. exit) would have shocked the planet," Schellnhuber said earlier this week. "Today if the U.S. really chooses to leave the Paris agreement, the world will move on with building a clean and secure future."

Katharine Hayhoe, a Texas Tech climate scientist, disagrees.

"There will be ripple effects from the United States' choices across the world," she told the AP.

James Crugnale and The Associated Press contributed to this report.

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