The White House did not confirm those reports, and it was unclear whether Trump would fully scrap United States participation, merely water down U.S. emissions objectives - or surprise everyone with a decision to follow the status quo. And one CEO who has been outspoken about climate action, Elon Musk of Tesla, has reportedly said he will quit serving on any of the Trump Administration's advisory councils if the US walks away from the COP21 deal. "If the president wants to be a leader of a great country - and we all agree that we want the U.S.to be great - if we're going to be great, we have to keep our word", he said. Even many of Trump's own advisers support the deal, according to The New York Times.
U.S. President Barack Obama, right, and U.N. Secretary-General Ban Ki-moon shake hands in front of Chinese President Xi Jinping during a joint ratification of the Paris climate change agreement at the West Lake State Guest House in Hangzhou in eastern China's Zhejiang province, Saturday, Sept. 3, 2016. Scientists say not doing so would result in catastrophic sea level rises and more frequent extreme weather events.
Under Obama, Washington had pledged to reduce greenhouse gas emissions by 26-28 percent below 2005 levels by 2025.
The CEOs of ExxonMobil Corp, Apple Inc, Dow Chemical Co, Unilever NV and Tesla Inc were among those urging Trump to remain in the agreement, with Tesla's Elon Musk threatening to quit White House advisory councils of which he is a member if the president pulls out.
"We tried to explain this in clear, simple sentences to Mr Trump in Taormina [Italy], but it would appear that he didn't understand".
Trump refused to endorse the accord at a summit of the G7 group of wealthy nations on Saturday in Italy, saying he needed more time to decide.
Everyone cautioned that no decision was final until Trump announced it.
Pulling away from efforts to reduce greenhouse gas emissions is expected to have significant repercussions on diplomacy between America and the other 194 participating nations.
The new move by the European Union and China was warmly welcomed by environmental campaigners, rattled by the prospect of the world's second largest emitter of carbon pulling out of the globally supported agreement.
The Sierra Club's executive director, Michael Brune, called the expected move a "historic mistake which our grandchildren will look back on with stunned dismay at how a world leader could be so divorced from reality and morality".
Trump was to announce at 3 p.m. EDT (1900 GMT) on Thursday whether he will keep the United States in the pact or take it out, and a source close to the matter said he was preparing to keep a campaign pledge to leave.
Basebrawl! Harper, Strickland punch away, Nats-Giants fight
Zimmerman hit a home run in the second inning and Daniel Murphy hit an RBI double off the bricks in the sixth. Giants manager Bruce Bochy acknowledged neither player will likely emerge covered in glory after the brawl.
Other European leaders issued more explicit appeals to the US government not to abandon worldwide measures against climate change.
The president could also announce that he will begin formally pulling out of the accord outright - a process that would take three-and-a-half years under the standard cooling-off period for new global treaties.
"Ignoring reality and leaving the Paris agreement could go down as one of the worst foreign policy blunders in our nation's history, isolating the US further after Trump's shockingly bad European trip", Democratic Senator Sheldon Whitehouse added.
USA coal company shares dipped alongside renewable energy stocks on Wednesday.
Other countries rallied behind the Paris accord on Wednesday.
A United States pullout would be disappointing but the European Union stands ready to take global leadership on the issue, European Commission Vice President Maros Sefcovic said in Brussels.
His daughter Ivanka had previously urged him not to pull the U.S. out of the agreement, which aims to keep global warming beneath 2degC by the end of the century.
The source, speaking on condition of anonymity, said Trump was working out terms of the planned withdrawal with U.S. Environmental Protection Agency Administrator Scott Pruitt, an oil industry ally and climate change doubter.
During his 2016 presidential campaign, Trump denounced the accord, and called global warming a hoax aimed at weakening USA industry. He also had to navigate a split among his advisers.
Coal firms such as Murray Energy and coal producing states such as Kentucky and West Virginia have urged him to abandon the Paris commitments.
Analysis by the Climate Interactive team said if the U.S. dropped out of the Paris Agreement and took no action, global temperatures could rise 0.3 degrees higher compared to if they stayed.