The planet is odds-on to hit 1.5C of global warming within 20 years, the world’s leading climate scientists will warn in a milestone report tomorrow.
The paper, produced by the UN’s Intergovernmental Panel on Climate Change (IPCC), is the starkest warning yet about the speed and scale of warming.
Experts said the report would paint a “devastating” picture. The document is predicted to trigger a “turning point” in the run-up to the Cop26 climate conference in Glasgow in November.
A 1.5C rise in average global temperatures on pre-industrial levels is widely considered to be the point beyond which climate change will become increasingly dangerous. The 2015 Paris Agreement committed countries to limiting warming to 1.5C. So far average temperatures have increased 1.2C.
The cabinet minister Alok Sharma, president of Cop26, said countries must work harder to reduce emissions and ensure the threshold is not breached. “This report will be a big wake-up call for countries to do even more,” he said.
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“I suspect the IPCC will reinforce the fact that we are running out of time. Glasgow will be about keeping 1.5C in reach. It will genuinely be a decisive moment in history.”
Tomorrow’s report, produced by 200 scientists from 60 countries, is the first comprehensive assessment of the physical science of climate change since 2013. An interim report, published in 2018, said global warming was likely to reach 1.5C between 2030 and 2052.
According to insiders who have seen the final document, the report brings this window forward by a decade to between 2021 and 2040.
The scientists have drawn up five scenarios for future warming, depending on whether the world continues to burn through fossil fuels. All five say it is “more likely than not”, at the very least, that the 1.5C threshold will be reached within this time period. Three of the five scenarios are more pessimistic, estimating that it is “likely”. Under the most optimistic scenario, temperatures are “more likely than not” to come back below 1.5C by the end of the century, with a temporary overshoot of no more than 0.1C. This would require a big cut in emissions.
Professor Ed Hawkins, a climate scientist at Reading University and a lead author of the report, declined to discuss the content of the paper, but said: “Every fraction of the degree matters. There’s no cliff edge where impacts suddenly go from being fine to being disastrous. It’s a gradual worsening of the impacts as global temperatures rise.”
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Scientists are more confident than ever about the extent to which extreme weather can be ascribed to climate change. He said: “This report goes into more detail about the various effects of climate change, about how it is already affecting us, particularly in terms of extreme events, and how it will continue to affect us in the future.”
Tom Rivett-Carnac, one of the architects of the Paris Agreement, said: “The IPCC report is going to be devastating in its reports of what is to come if we don’t deal with this. The increasing natural disasters, and the presence of the [Cop26] event so close on the horizon, will, I think, turn this into quite an interesting turning-point moment over the course of the next few weeks.”
The report is expected to detail the risk of “tipping points”, in which climate change becomes hard to reverse. The melting of glaciers and ice sheets, for example, may create “feedback loops” in which global warming spirals out of control. “That sensitivity means you can be too late,” Rivett-Carnac said. “A lukewarm agreement [at Glasgow] that kicks the can down the road and solves some problems, has become, in a way, as much something to be avoided as not reaching the outcome you want.”
