COP26 is the “last opportunity” for humanity to prevent global temperature rises passing 1.5C, the Prime Minister has said.

With world leaders preparing to descend on Glasgow for the crucial climate summit, where countries are under pressure to increase their ambition to tackle the greenhouse gas emissions driving climate change, Boris Johnson said the human race had entered the last chance saloon on the environment.

He said the focus needed to be on securing agreements for countries to cut their carbon output and stop global warming exceeding the target amount to prevent the worst impacts.

Speaking to the i newspaper, Johnson said: “COP is really the last opportunity for the planet, humanity, to come together and keep alive the hope of restricting growth in temperatures to 1.5 degrees.

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“We are not going to stop climate change any time soon, and we are certainly not going to stop it at COP26.

“The most we can hope to do, and it is going to be incredibly difficult, is to restrict the growth by the end of the century to 1.5 degrees.”

He predicted the talks would involve a “massively complicated negotiation of trade-offs between the developing world and richer countries” which could last for “days and days” in the bid to find an agreement at the two-week conference.

In separate comments to reporters on his flight to the G20 in Rome, Johnson revealed he had urged China’s President Xi Jinping to move faster on reducing his country’s carbon emissions.

The Prime Minister said he had a lengthy telephone call with Xi ahead of COP26 – which the Chinese leader is not attending – during which he raised the issue of when China’s emissions would peak.

“They said before 2030, obviously I pushed a bit on that – ’25 would be better than 2030. But then I wouldn’t say he committed on that,” he said.

“The other point where I was evangelical was the potential to move away from coal. He said China depends on coal for… domestic economy and I said the thing you’ve heard me say so many times about the UK moving away from 80% dependence on coal to 1% today.

“I said when I came to see you in Beijing in 2008 we were 40% dependent on coal – it shows how fast you can make the transition.”

Johnson, who read classics at Oxford University, used the example of the Roman Empire to show how swiftly civilisations can collapse as he urged action among G20 leaders on climate change ahead of the UK summit.

“When things start to go wrong they can go wrong at extraordinary speed,” he said.

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“You saw that with the decline and fall of the Roman Empire, and I’m afraid to say it’s true today that unless we get this right in tackling climate change, we could see our civilisation, our world, also go backwards.

“There is absolutely no question this is a reality we must face up to.”

Switching to a football analogy, the Conservative Party leader said that “if this was half-time, I’d say we were about 5-1 down” in the battle against climate change.

But he stressed that we “can do it”, adding: “We have the ability to equalise, to save the position and to come back, but it’s going to take a huge amount of effort by the British Government, by all our friends and partners around the world.”