The United States is now the only country on Earth that's declined to be a part of the Paris climate agreement, after Syria announced Tuesday it would join the landmark 2015 pact.

In an address to delegates at a global climate meeting in Bonn, Germany, Syria’s deputy minister of local administration and environment, M. Wadah Katmawi, said his country would join the Paris deal “as soon as possible.”

The Paris agreement aims to combat global warming by gradually reducing emissions of greenhouse gases such as carbon dioxide and methane, which come from the burning of fossil fuels such as oil, coal and natural gas. President Trump announced in June that the U.S. would withdraw from the deal.

“Syria’s announcement that it will join the Paris agreement leaves President Trump in not-so-splendid isolation as a result of his irresponsible and ignorant decision to withdraw the United States from the most comprehensive effort ever to confront the mounting climate crisis," said Alden Meyer, of the Union of Concerned Scientists.

The U.S. is the second-largest carbon dioxide-emitting nation on the planet after China, according to the European Commission. After hearing about Syria's decision, Sen. Dick Durban, D-Ill., called it "embarrassing" for the U.S., while Sen. Tim Kaine, D-Va., said that "by 'America first,' they meant America last."

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If emissions are reduced as spelled out in the agreement, scientists and policymakers say it will prevent a major increase in global temperatures that would raise sea levels, spark major droughts, and lead to more dangerous storms.

When the pact took effect in 2016, environmental groups and political leaders heralded it as a critical step in trying to reverse man-made ravages on the global environment. Syria had been the last nation, other than the U.S., not to be a part of the agreement.

Calling it "Draconian" and "onerous," Trump in June said "the Paris Climate Accord is simply the latest example of Washington entering into an agreement that disadvantages the United States to the exclusive benefit of other countries, leaving American workers — who I love — and taxpayers to absorb the cost in terms of lost jobs, lower wages, shuttered factories, and vastly diminished economic production."

If the Trump administration follows through with its threat, the U.S. withdrawal would take effect in November 2020, on the day after the presidential election.

The only other previous holdout, Nicaragua, announced in September that it would join the pact.

"As if it wasn't already crystal clear, every single other country in the world is moving forward together to tackle the climate crisis, while Donald Trump has isolated the United States on the world stage in an embarrassing and dangerous position," Sierra Club executive director Michael Brune told EcoWatch, in response to Syria's move.

Climate meeting in Germany

The news about Syria came during the second day of the United Nations' Climate Change Conference in Bonn, Germany. Some 25,000 scientists, envoys, lobbyists and environmental activists have descended on the city for two weeks to figure out how to turn the goals of the Paris accord into reality.

The U.S. did not set up a pavilion at this year's meeting — the only developed country not to do so, according to Deutsche Welle, a German news agency.

However, governors, mayors and business leaders from the U.S. will set one up there later this week. “While the White House declares war on climate science and retreats from the Paris Agreement, California is doing the opposite and taking action," said California Gov. Edmund G. Brown, Jr., who will be going to the meeting.

"We are joining with our partners from every part of the world to do what needs to be done to prevent irreversible climate change,” he said.

2017 another hot year

At the meeting Monday, the United Nations' weather and climate agency, the World Meteorological Organization, announced 2017 will definitely be among the three hottest years on record. The hottest on record was 2016, followed by 2015.

"This is part of a long-term warming trend,” said WMO Secretary-General Petteri Taalas. “We have witnessed extraordinary weather, including temperatures topping (122 degrees Farenheit) in Asia, record-breaking hurricanes in rapid succession in the Caribbean and Atlantic reaching as far as Ireland, devastating monsoon flooding affecting many millions of people and a relentless drought in East Africa.

“Many of these events bear the tell-tale sign of climate change caused by increased greenhouse gas concentrations from human activities,” he said.

The WMO also said 2017 will be the hottest non-El Niño year ever recorded. El Niño is a powerful natural climate pattern marked by unusually warm water in the tropical Pacific Ocean, which can contribute to higher global temperatures.

Contributing: Associated Press