That’s according to a number of charities and environmental groups, including Oxfam, RSPB, Greenpeace UK, WWF and Christian Aid.
In a joint letter published today, the heads of these organisations said the Prime Minister needs to “pick up the phone” to her counterpart in the US and remind him of the possible consequences of backing out of the deal.
That follows media reports that support for leaving the climate treaty is gaining ground among Donald Trump’s key advisers, although Trump is yet to make a final decision, which is expected this week.
Mrs May is seen as a key world influence on Mr Trump – a Greenpeace petition urging her to intervene in the matter has gathered more than 80,000 signatures since Thursday night.
The Prime Minister previously urged the US to work with the United Nations to tackle climate change.
Global investors worth more than $15 trillion (£11.6tn) have signed a letter calling for G7 and G20 nations to stand by their commitments to the Paris Agreement.