The Labour Party is urging Theresa May to formally ratify the landmark climate deal agreed in Paris last year.
In a letter to the Prime Minister, Shadow Energy Secretary Barry Gardiner warns if the UK lags behind its global partners, it would “greatly damage” the nation’s “strong reputation” for climate diplomacy.
Around 55 countries representing 55% of global emissions are required for adoption but so far only 23 have ratified, representing 1.08% of emissions.
The US and China account for 40% of the world’s carbon pollution.
Mr Gardiner adds: “After the vote to leave the European Union, our international partners will be paying close attention to whether the UK continues to have an outward, responsible internationalise perspective or turns inwards.
“I believe it is essential that you take this opportunity to demonstrate that the UK remains committed to playing its part on the global stage.”
He is calling on the government to take the necessary steps to start the procedures and complete the process before the end of the year.
A government spokesperson said: “Climate change remains one of the most serious long term risks to our economic and national security and one of the most serious threats facing our world. The UK’s commitment to tackling it, internationally and domestically, is as strong as ever.
“We are committed to ratifying the Paris Agreement as soon as possible.”