Parts of the world will still disappear under water even if Cop26 achieves its climate target, the summit’s president Alok Sharma has warned.
The United Nations conference in Glasgow gets under way on Sunday, with the UK pressing world leaders to sign up to prevent global temperatures from rising by more than 1.5C above pre-industrial levels.
Mr Sharma said it will be a “tough ask” to reach the objective, with the global political situation “more difficult” than when “historic” agreements were struck in Paris in 2015.
The former business minister said he hopes political leaders emerge from the two weeks of talks with “credibility”, having “kept 1.5C alive”.
His comments come as Prime Minister Boris Johnson is pushing world leaders at the G20 summit in Rome to go further on their climate pledges, arguing Glasgow represents the “best chance” of safeguarding the future of the planet.
Mr Sharma told Sky News’ Trevor Phillips On Sunday programme that “1.5C really matters”.
He added: “We know from the IPCC (the Intergovernmental Panel on Climate Change) that we are already at global warming of 1.1C above pre-industrial levels.
“At 1.5C, there will be countries in the world that will be under water and that’s why we need to get an agreement here on how we tackle climate change over the next decade.”
Marshall Islands climate envoy Tina Stege has said her country will be gone within the next 50 years if nothing is done about climate change, with even a 1.5C rise “unimaginable” for the nation, which sits just two metres above sea level.
Lord Deben, chairman of the independent Climate Change Committee, said 1.5C “has to be attainable” in Glasgow or it will not just be the Marshall Islands fearing for its future, but parts of Europe as well.
“All that we have to defend and it’s, I’m afraid, a battle which we just have to win. It’s like, in that sense, the Battle of Britain – we cannot possibly lose it.”
Downing Street said Cop26 will be one of the biggest events the UK has ever hosted, with 25,000 delegates expected from 196 countries and the European Union.
Ministers, climate negotiators, civil society and business leaders are set to take part in talks and debates over the course of the conference.
Environmental campaigner Greta Thunberg is among those to have journeyed to Glasgow, having taken a train to the Scottish city from London on Saturday.
The 18-year-old told the BBC’s Andrew Marr Show she believes it is “possible in theory” to reach an agreement to keep global warming below 1.5C, adding: “It’s up to us if we want that to happen.”
Mr Johnson, who is at the G20 summit in the Italian capital and due to travel to Cop on Sunday evening, will tell world leaders that time is running out to save civilisation from the impact of climate change.
No 10 said the Prime Minister will point out that while there has been progress in recent weeks, “barely half” of the G20 have set out more ambitious plans for cutting carbon emissions since 2015 and there are still two members who have not committed to creating a net-zero carbon economy.
The Prime Minister said that in Glasgow, “humankind will gather to fight for the future of the planet”.
He added: “Glasgow represents our best chance. Just as the G20 shares a collective responsibility to act, so the solutions are in our hands.
The summit timetable will see the Prime Minister host an opening ceremony, attended by dignitaries including the Prince of Wales, before giving a speech on Monday.
Charles and Sir David Attenborough, the Cop26 “people’s advocate”, will be among those to also address world leaders as British environmentalists.
On Monday evening, the Prime Minister will host a reception to welcome world leaders to Glasgow, alongside the Duke and Duchess of Cambridge and the Duke and Duchess of Cornwall.
The Queen will address the delegates in a pre-recorded video after she was told by doctors to avoid the summit and rest following her recent hospital visit.