Under the Paris Accord, almost 200 nations agreed in 2015 to voluntarily cut greenhouse gas emissions in a landmark agreement to fight climate change.
The U.S.is the second worst emitter of carbon dioxide in the world, according to the European Commission's emissions database, behind only China.
U.S. President Donald Trump is due to announce later on Thursday if he will quit the global climate deal. A White House official told The Associated Press on Wednesday that Trump is expected to withdraw from the deal, though aides cautioned he had not yet made a final decision. The exit could take as long as one to nearly four years.
He added he would have "no choice" but to depart Trump's advisory councils if the United States pulled out of the climate deal. That means leaving the agreement isn't the only way to weaken it: Trump could have kept the U.S.as a signatory, but continued to slash the programs that would actually make it possible to reach the target for emissions. On the campaign trail, he criticized the agreement that the USA formally signed onto a year ago.
What is the Paris Agreement, anyway?
Global average temperatures have hit record highs in each of the past three years, and warming is projected to cause worsening droughts, sea level rises, floods, heat waves and extinctions of wildlife. During the presidential campaign, Trump pledged to "cancel" the Paris accord within his first 100 days of office. The president has pledged to reverse decades of decline in coal mining, which now accounts for fewer than 75,000 U.S.jobs.
Scientists say Earth is likely to reach more unsafe levels of warming sooner if the US retreats from its pledge because America contributes so much to rising temperatures.
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Agreed to at the 21st Conference of Parties, or COP21, in 2015, the Paris Agreement had just one major aim - to keep average global warming due to climate change to within the risky 2 degree Celsius (3.6 degrees Fahrenheit) threshold.
"It was a significant move forward. the fact that there's just so much agreement and good will on all parts, including some nations that had been (reluctant) in the past", said Professor Ian Simmonds of Sydney University's School of Earth Sciences.
Trump's influential daughter Ivanka Trump's preference is to stay, but she has made it a priority to establish a review process so her father would hear from all sides, said a senior administration official.
"Nevertheless, Germany owes vast sums of money to North Atlantic Treaty Organisation and the United States must be paid more for the powerful, and very expensive, defense it provides to Germany", Trump said in a two-tweet statement after meeting with Merkel for the first time in March.
California has also previously said it would help pick up the slack for any backdowns by the USA president on climate change.
Every nation involved in the talks, except Syria and Nicaragua, signed onto the deal. "The declines in US emissions in the last decade have largely happened without strong climate policies, and a withdrawal from the Paris Agreement may have minimal effect on USA emissions but give a hit to global morale".
Paul Bodnar, a former Obama climate change adviser, says it wouldn't afford the USA even a sideline view of the climate conversations.