Boris Johnson has compared the risks of climate change to the fall of the Roman Empire, as the UK Prime Minister said a failure to act could see civilisation swiftly going backwards.
G20 leaders are meeting in Rome at the weekend, with global warming a key talking point.
Nearly 200 world leaders and around 20,000 delegates will also gather in Glasgow, Scotland, from Sunday for the Cop26 UN climate conference.
Mr Johnson said it would be “very, very tough” to get the agreements needed to slow the temperature rise.
A leaked draft of the final G20 communique said they would enhance effort to limit global warming to 1.5°C above pre-industrial levels.
This is generally regarded as the level necessary to avoid the most severe effects of climate change.
“Humanity, civilisation and society can go backwards as well as forwards, and when they start to go wrong, they can go wrong at extraordinary speed,” Mr Johnson said in Rome.
“Unless we get this right in tackling climate change, we could see our civilisation, our world, also go backwards.
“You saw that with the decline and fall of the Roman Empire.”
Mr Johnson has not struck an optimistic tone in the lead-up to the conference, saying in Rome that he still rated the chances of success in Glasgow as no more than six out of 10.
G20 countries account for around 80 per cent of global emissions and the world's gross domestic product.
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People demonstrate on the sidelines of a G20 environment meeting in Naples, Italy. -
Police officers face demonstrators protesting in Naples. Environment and energy ministers from the Group of 20 industrialised countries are meeting in Naples ahead of November's crucial UN climate change conference. -
A protestor throws an inflatable globe into the air. Host Italy is hoping the talks will help spur ambitious goals to be adopted at the Cop26 conference in Glasgow. -
Protesters cover a mockup coffin during the protests. -
People hold a banner reading in Italian 'The G20 dances on Titanic, let's Save the planet, go away!'. -
Demonstrators wear facemasks during the protest in Naples. -
Protesters from Extinction Rebellion wear masks depicting Boris Johnson, Angela Merkel, Joe Biden, Jair Bolsonaro, Vladimir Putin and Mario Draghi. -
Protesters, including members of Extinction Rebellion and Fridays for Future, march through Naples. -
A person holds a placard depicting the Earth with a temperature. -
A protester wears a mask bearing the slogan 'No G20'.
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An aerial view of the Scottish Events Centre in Glasgow, where the Cop26 Summit will take place from Sunday, October 31, until Friday, November 12. Getty Images -
Banners advertising the upcoming Cop26 Summit line a street in Glasgow. Glasgow was chosen to host the summit in 2019. Ministers described it as one of the UK’s most sustainable cities and a showcase for “diverse culture and world-leading innovation”. Bloomberg -
Workers erect a fence at the Scottish Events Centre. Cop26 was initially due to take place in 2020 but was postponed by a year because of the pandemic. Getty Images -
A pupil holds a poster at St Convals Primary School in Glasgow while learning about climate change ahead of Cop26. About 25,000 people are expected to attend the summit. Reuters -
Road closures are in place around the SEC in Glasgow. There have been 25 Conference of the Parties (or 'Cop') summits so far, making this year's event 'Cop26'. Bloomberg -
An electronic poster advertising the Cop26 summit. World leaders will kick off the summit by setting 'high-level ambition' for climate action, the UK government says. Bloomberg -
The Armadillo building forms part of the SEC, the location for the summit. Bloomberg -
Artists paint a mural on a a wall next to the Clydeside Expressway near the SEC. Getty Images -
Police Scotland mounted officers patrol near the SSE Hydro venue in Glasgow. As part of the summit, world leaders are holding talks on November 1 and 2. Prime Minister Boris Johnson will represent Britain and US President Joe Biden will be there. AFP -
Volunteers model the official uniforms that will be worn by about 1,000 volunteers at Cop26. PA
“From the pandemic, to climate change, to fair and equitable taxation, going it alone is simply not an option,” said the host of the G20 talks, Italian Prime Minister Mario Draghi.
A draft communique seen by Reuters said leaders are set to pledge to halt financing of overseas coal-fired power generation by the end of this year, and to “do our utmost” to stop building new coal power plants before the end of the 2030s.
But G20 members, many at different stages of economic development, remain at odds over the goal of reducing greenhouse gas emissions to net zero by 2050.
Climate is expected to feature more prominently at the G20 talks on Sunday, with the first day largely focused on Covid-19 and the economic recovery.
Leaders are also expected to approve a global minimum corporation tax of 15 per cent.
