Campaigners have reacted angrily to reports that President Donald Trump is poised to pull the US out of the Paris Agreement.
The world's first comprehensive climate deal, secured in the French capital in December 2015, commits countries to emissions cuts that will keep global temperature rises to "well below" 2C above pre-industrial levels.
The US signed up to the hard-won agreement under former president Barack Obama, but Mr Trump promised to abandon the deal during his election campaign and to boost fossil fuels.
The possibility Mr Trump - who has previously described climate change as a hoax by the Chinese - could pull out within days was labelled disastrous and as putting the US on "the wrong side of history" in some quarters.
But many were quick to say the transition to a clean economy was now unstoppable.
There were also calls for the UK, which confirmed its commitment to climate action with the other G7 leading nations apart from the US in recent days, not to do trade deals with America if it pulled out.
Rumours already swirling about the future of US involvement in the Paris deal were further stoked when Mr Trump tweeted on Wednesday: "I will be announcing my decision on the Paris Accord over the next few days. MAKE AMERICA GREAT AGAIN!"
Nick Dearden, director of Global Justice Now, said: "Amidst the series of ill-informed and autocratic policies that Trump has enacted since coming to power, his decision to pull out of the Paris accord stands out as the one that will have the most long-term and disastrous consequences for the world.
"Despite the US having been responsible for a massively disproportionate share of historic greenhouse gas emissions, it is now washing its hands of the situation while billions of the world's most vulnerable peoples will face the fatal consequences of rising sea levels, drought, desertification and failing crops.
"At such a critical juncture in the international fight against the worst impacts of the climate crisis, global leaders should be refusing to enter into trade negotiations with the US as a proportionate response to this supremely reckless act of climate vandalism."
Tearfund's head of advocacy Paul Cook said: "World leaders need to uphold their commitments to prevent lives and livelihoods being hit hard by an unstable and changing climate.
"It is disappointing that President Trump does not see the opportunity for economic growth which clean energy presents - emerging economies such as China and India are discovering how renewable energy can be a catalyst for a booming economy, creating green jobs and flourishing businesses, while reducing carbon emissions."
He added: "Now, more than ever, we need to unite in our personal commitment to living sustainably."
Friends of the Earth's chief executive Craig Bennett said the organisation would campaign against any trade deal with the US if it "turns its back on its global responsibility to tackle climate change" .
"This short-sighted and dangerous decision will be met by opposition around the world: from ordinary people, to scientists, and political leaders - making the US a global outcast.
"Whoever becomes the next UK prime minister, they must now step up on climate action and show that our 'special relationship' with the US cannot extend to supporting a nation that would so flippantly jeopardise the climate for future generations, " he said.
Anthony Hobley, chief executive of the Carbon Tracker Initiative, said: "The abandonment of the Paris Agreement by the Trump administration, if confirmed, is an economic and leadership failure of monumental proportions and will sadly cast the US on the wrong side of history.
"The rest of the world and key parts of the US economy, such as California, will get on with implementation regardless.
"Our financial analysis shows beyond doubt that the low carbon transition underway is driven by unstoppable technological change and innovation."
Solar jobs and electric vehicles are booming while China and India are already on track to meet or even surpass their climate commitments, he said.
The looming decision by the US comes as the European Union and China look set to commit to deeper action on climate change at a summit on Friday.
Ahead of the meeting, EU Climate Action Commissioner Miguel Arias Canete said: "No one should be left behind, but the EU and China have decided to move forward."
Cabinet minister Amber Rudd - who helped negotiate the Paris agreement while she was climate change secretary - said she was "disappointed" by Mr Trump's stance.
The Home Secretary, appearing on a BBC election debate, said: "It is disappointing that the Americans are pulling out but I hope that we can use our relationship with President Trump and our close relationship with the US to try and influence, to try and make sure that they nevertheless take the right steps."