'There is no chance of stopping climate change next week,' the Prime Minister told me in an interview for ITV News. 'There is no chance of getting an agreement to limit climate change to 1.5 degrees'.
Standing in Rome's magnificent ancient Colosseum, he warned that the cost of this failure, if not somehow rectified, would be far worse than the recent pandemic: 'The Romans thought they were going to go on forever...Then wham, the middle of the fifth century, they hit a complete crisis, uncontrolled immigration, you have the Dark Ages. The lesson is things can go backwards... for a long time. Unless we fix climate change, unless we halt that massive growth in temperatures, that's the risk we run"'
But if COP26 has already failed, as the PM seems to be saying – because the world's biggest emitters are such a long way from promising measures to cut greenhouse gas emissions by the necessary 55 per cent before 2030 – why on earth are more than 100 world leaders descending on Glasgow for the negotiations?
Also what's the point of this weekend's preceding discussions in Rome of the G20 leaders of the world's most powerful nations? For Boris Johnson, COP26 is what he calls a 'weigh station', a checkpoint on a route towards future agreements that would stand a chance of reducing global warming to a safe increment.