President Donald Trump announced that the United States would pull out of the Paris climate agreement during a speech in the White House Rose Garden on June 1, 2017.

The Paris climate agreement is an international accord negotiated by almost 200 countries, aimed at curbing climate change by reducing greenhouse gas emissions. It is considered one of the strongest environmental policy legacies of President Barack Obama's tenure in office, who called it "a turning point for our planet."

In the Rose Garden ceremony, Trump said that the the United States would exit the Paris agreement.

"As of today, the U.S. will cease all implementation of the non-binding Paris accord and the draconian financial and economic burdens the agreement imposes on our country," Trump said.

In his lengthy remarks, Trump painted a dystopian picture of an American economy ruined by international agreements that benefit its rivals. He called the Paris agreement "the latest example of Washington entering into an agreement that disadvantages the United States," and added that "I cannot in good conscience support a deal that punishes the United States."

"I was elected to represent the citizens of Pittsburgh, not Paris," he said. (Pittsburgh mayor Bill Peduto tweeted after Trump's announcement that "as the Mayor of Pittsburgh, I can assure you that we will follow the guidelines of the Paris Agreement for our people, our economy & future.")

All of the world's nations but Syria and Nicaragua had signed the agreement.

Trump did leave a sliver of an opening for another climate agreement in the future. He said the United States would "begin negotiations to re-enter either the Paris accord or an entirely new transaction on terms that are fair" to the United States, its workers and its taxpayers.

"We will see if we can make a deal that's fair, and if we can, that's great," he said. "If we can't, that's fine."

The departure from the Paris agreement followed Trump's earlier decision to shelve another signature environmental effort by Obama, his 2013 Climate Action Plan.

Obama had pledged to reduce emissions by 26 percent to 28 percent below 2005 levels by 2025. Trump, by contrast, has at times dismissed climate change as a hoax. (It's not.)

Moments after Trump made his announcement, Obama released a statement. "The nations that remain in the Paris Agreement will be the nations that reap the benefits in jobs and industries created," Obama said. "I believe the United States of America should be at the front of the pack. 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."

Trump's decision to leave the Paris agreement was broadly telegraphed in the days leading up to the announcement, but after his victory in the 2016 election, he had wavered a bit on whether to keep his promise to abandon the agreement. For instance, he told a New York Times reporter in late November 2016 that "I'm looking at it very closely. I have an open mind to it."

Trump reportedly was whipsawed by key advisers on the issue. Economic nationalists in White House, including counselor Steve Bannon, have pushed for an exit, while his daughter, Ivanka Trump, and leading business officials have urged him to remain in the agreement.

For instance, before Trump had finished his speech, General Electric CEO Jeffrey Immelt tweeted, "Disappointed with today's decision on the Paris Agreement. Climate change is real. Industry must now lead and not depend on government."

It could take anywhere between a year and four years to formally disentangle the United States from the agreement, experts say.

A potential winner from the United States' departure from the accord would be the coal industry, since coal is a major carbon emitter. During the 2016 campaign, Trump was a strong supporter of coal, and coal producing areas such as West Virginia were among his most enthusiastic bases of support.

However, it's not clear that the coal sector can rebound in a significant way even with U.S. withdrawal from the Paris agreement. Business factors (particularly the increasing competitiveness of natural gas secured through hydraulic fracturing, or "fracking") and technological developments (including the technological refinement of renewable energy sources such as solar and wind) have taken up an increasing share of the energy used for electricity generation in the United States and overseas.

The Paris agreement stems from an earlier international agreement, the United Nations Framework Convention on Climate Change. That accord was adopted in 1992 and entered into force in 1994. It consists of 197 parties (196 States and 1 regional economic integration organization).

During a December 2015 session in Paris, parties to the 1992 agreement adopted what became known as the Paris Agreement, seeking "to strengthen the global response to the threat of climate change." One of the objectives is to hold the increase in global average temperature well below 2 degrees Celsius above pre-industrial levels. The agreement does not impose penalties on signatories, nor does it specify how each country should meet the targets, but the idea behind the agreement is that mutual peer pressure will keep member nations in line.

A total of 175 parties signed the Paris agreement on April 22, 2016. The Paris Agreement came into effect in November 2016 after 55 countries accounting for at least 55 percent of total global greenhouse gas emissions formally ratified the agreement. All told, 195 nations signed the agreement and 147 parties have ratified it through April 21, 2017.

The United States is now on its way to joining Syria (which was engaged in a deadly civil war during the negotiations) and Nicaragua (which said the agreement didn't go far enough) as the only signatories to the 1992 agreement that did not also sign the Paris agreement.

Even North Korea ratified the agreement in 2016.

For now, there are signs that the European Union and China were ready to recommit to the agreement regardless of whether Trump decided to keep the United States in the agreement or not. However, critics said the eventual departure of the United States could weaken the deal, among other things depriving it of tangible progress by the world's second biggest carbon emitter.

In his speech, Trump did not specify the mechanism by which the United States would leave the agreement.

There are a few formal options Trump could follow. The slowest option would be withdrawing from the agreement. Under article 28.1 of the agreement, countries can withdraw by giving one year's notice, starting three years after the Paris agreement takes force.

The Paris Climate Accords started on Nov. 4, 2016, so in early November 2019, Trump could give written notice and be withdrawn from the agreement the following year.

Alternately, Trump could withdraw from its parent agreement, the United Nations Framework Convention on Climate Change. Article 28.3 of the Paris agreement says that "any party that withdraws from the Convention shall be considered as also having withdrawn from this Agreement." Trump would need Senate approval to withdraw from the convention.

As far as the second part of Trump's promise -- ending United States funding of United Nations global-warming programs -- Trump stuck to his guns on that as well.

Under Obama, the United States sent the first $1 billion of a $3 billion pledge to United Nations' Green Climate Fund. But additional payments have not been forthcoming under Trump.

In his Rose Garden speech, Trump said the fund amounts to an unjustified redistribution of U.S. taxpayer money. While needs at home go unmet, Trump said, money from the fund "will be sent to the very countries and factories that have taken our jobs."

He said his moves amounted to a reassertion of American sovereignty.

So how do we rate this promise? While Trump did leave open the possibility that the United States could rejoin the agreement if it's renegotiated, it's not clear when -- or if -- that could happen. The bottom line is that, even though it isn't immediate, he has set in motion the United States' exit from the Paris agreement, and he also pledged to stop funding U.N. global warming efforts, fulfilling both parts of his campaign promise. We rate it a Promise Kept.

The election of Donald Trump has heated up climate change debate, as many of his promises look to roll back environmental regulations.

Perhaps the most notable of these promises was Trump's oft-repeated campaign pledge to cancel U.S. participation in the Paris climate agreement — an international accord negotiated by almost 200 countries aimed at curbing climate change and reducing greenhouse gas emissions.

On the campaign trail, Trump took a hard stance against the Paris climate agreement and vowed to pull the United States out of it. Since then, however, Trump has signaled he might back off of his promise, telling a New York Times reporter in late November, "I'm looking at it very closely. I have an open mind to it."

WHY HE'S PROMISING IT

Trump has championed slashing environmental regulations so he can increase drilling and energy production in the United States.

Trump also griped about the financial impact of the Paris agreement and Obama's actions to get it passed. In September 2016, Obama ratified the deal without the approval of Congress, which was criticized by Republican lawmakers for pushing constitutional limits.

"This agreement gives foreign bureaucrats control over how much energy we use right here in America," Trump said "We're going to cancel the Paris Climate Agreement and stop all payments of U.S. tax dollars to U.N. global warming programs."

WHAT NEEDS TO HAPPEN

There are a few formal options Trump could go about in order to cancel the Paris agreement. The slowest option would be withdrawing from the agreement. Under article 28.1 of the agreement, countries can withdraw by giving one year's notice, starting three years after the Paris agreement takes force.

The Paris Climate Accords started on Nov. 4, 2016, so in early November 2019, Trump could give written notice and be withdrawn from the agreement the following year.

Trump also could withdraw from its parent agreement, called the United Nations Framework Convention on Climate Change.

Josh Howe, a environmental science professor at Reed College, said it's unlikely Trump will take the above options. 

Article 28.3 of the Paris agreement says that "any party that withdraws from the Convention shall be considered as also having withdrawn from this Agreement." Trump would need Senate approval to withdraw from the convention.

Ann Carlson, an environmental law professor at the University of California-Los Angeles, said there are informal options Trump could take, too.  He could simply say that the United States will not meet its obligations under the agreement and allow us to be in violation of international law.

He also could argue that the United States will meet obligations set forth by the Paris agreement without relying on the Clean Power Plan, which is the centerpiece of the United States' Nationally Determined Commitment.

"With trends in the electricity sector in the U.S. moving us away from coal and toward natural gas and renewables, we will probably meet our mid-term obligations for the electricity sector even without the CPP," Carlson said.

Howe echoed Carlson's point, and added that the Pairs agreement has no formal enforcement mechanism.

And as for diplomatic concerns, we can only speculate at this point what the effects will be.

TIMELINE

Depending on the route Trump takes, it could take anywhere between a year and four years to withdraw from the agreement formally.