Donald Trump's election victory puts a climate change denier back in the White House, poised to dismantle his predecessor's green policies and jeopardize global efforts to curb human-caused warming.
The Republican revived his "drill, baby, drill" slogan during his campaign and in his victory speech described US oil and gas reserves as "liquid gold".
Experts warn that a second Trump presidency would slam the brakes on the transition to green energy, hindering efforts to meet crucial climate targets.
The impact will likely be felt even before his January inauguration.
His election saps the influence of US negotiators at the COP29 UN climate summit, kicking off on November 11 in Azerbaijan.
A US retreat from climate diplomacy could seriously undermine global action to cut fossil fuel reliance, potentially giving other heavy polluters like China and India an excuse to scale back their own plans.
"With Trump's win, we now face, at best, a repeat of his last term's climate inaction -- a four-year pause we simply can't afford in this critical decade," said Johan Rockstrom, a climate scientist and director of the Potsdam Institute for Climate Impact Research.
"With a climate sceptic back in the White House, the pressure on the world, and especially on EU leadership, to act will intensify enormously."
Trump's track record looms large. During his first term he withdrew from the landmark Paris Agreement and has vowed to do so again, after US President Joe Biden brought the world's second-biggest emitter back into the fold.
The formal exit procedure takes a year from notification, meaning the United States would technically stay on board until 2026, if only on paper.
"It's worse than 2016. And not only in the United States," Laurence Tubiana, the architect of the Paris deal, told AFP.
"It will take an unprecedented mobilization so that the shock of the American decision does not impact other countries that have become reluctant to accelerate action."
Under the Paris Agreement, Washington pledged to halve its greenhouse gas emissions by 2030 compared to 2005 levels. By 2023, emissions had fallen by 18 percent, according to the Rhodium Group.
But a Carbon Brief analysis warns that a Trump comeback could result in an additional four billion metric tons of CO2 equivalent emissions by 2030 -- roughly the annual emissions of the European Union and Japan combined.
"The outcome of the American election will have ramifications for the whole planet," Leah Stokes, a political scientist at the University of California, Santa Barbara, who specializes in climate, told AFP.
Efforts to curb warming and protect against increasingly-costly climate change impacts "hang in the balance", particularly for vulnerable poorer nations, said Joyce Banda, the former President of Malawi.
"As a global superpower, we expect the US to do the right thing for the sake of the world and generations to come."
Climate action at home is also in Trump's sights.
He has vowed to "rescind all unspent funds" in the Inflation Reduction Act, Biden's signature climate law funneling hundreds of billions of dollars into tax credits and clean energy investments.
But dismantling a law isn't simple.
Even some Republicans see the benefits of its tax incentives and are reluctant to gut it.
Trump has also pledged to end Biden's moratorium on new liquefied natural gas (LNG) export permits and strike down what he dubs the "electric vehicle mandate" -- actually a set of emissions standards aimed at boosting EV adoption, which are not mandates at all.
Newly minted US Environmental Protection Agency rules aimed at slashing carbon emissions from fossil fuel power plants could also find themselves on the chopping block.
"I do expect to see a fair amount of litigation over any efforts to repeal these regulations," Fatima Ahmad, of the climate consulting firm Boundary Stone Partners, told AFP.
She also expects that state and local governments, along with private sector initiatives, will continue advancing climate action, echoing the momentum seen during Trump's first term.
But despite these efforts, the potential national and international impact remains staggering.
