New research suggests the Earth’s climate could be more sensitive to greenhouse gases than thought, raising the spectre of an ‘apocalyptic side of bad’ temperature rise of more than 7C within a lifetime
- Ian Johnston Environment Correspondent
- Wednesday 9 November 2016
If the Earth’s temperature rises seven degrees Celsius, it could trigger the kind of runaway global warming that may have turned Venus from a habitable planet into a 460C version of hell.
It is a vision of a future so apocalyptic that it is hard to even imagine.
But, if leading scientists writing in one of the most respected academic journals are right, planet Earth could be on course for global warming of more than seven degrees Celsius within a lifetime.
And that, according to one of the world’s most renowned climatologists, could be “game over” – particularly given the imminent presence of climate change denier Donald Trump in the White House.
Scientists have long tried to work out how the climate will react over the coming decades to the greenhouse gases humans are pumping into the atmosphere.
According to the current best estimate, by the Intergovernmental Panel on Climate Change (IPCC), if humans carry on with a “business as usual” approach using large amounts of fossil fuels, the Earth’s average temperature will rise by between 2.6 and 4.8 degrees above pre-industrial levels by 2100.
However new research by an international team of experts who looked into how the Earth’s climate has reacted over nearly 800,000 years warns this could be a major under-estimate.
Because, they believe, the climate is more sensitive to greenhouse gases when it is warmer.
A reconstruction of the Earth’s global mean temperature over the last 784,000 years, on the left of the graph, followed by a projection to 2100 based on new calculations of the climate’s sensitivity to greenhouse gases (Friedrich, et al. (2016))
In a paper in the journal Science Advances, they said the actual range could be between 4.78C to 7.36C by 2100, based on one set of calculations.
Some have dismissed the idea that the world would continue to burn fossil fuels despite obvious global warming, but emissions are still increasing despite a 1C rise in average thermometer readings since the 1880s.
And US President-elect Donald Trump has said he will rip up America’s commitments to the fight against climate change.
Professor Michael Mann, of Penn State University in the US, who led research that produced the famous “hockey stick” graph showing how humans were dramatically increasing the Earth’s temperature, told The Independent the new paper appeared “sound and the conclusions quite defensible”.
“And it does indeed provide support for the notion that a Donald Trump presidency could be game over for the climate,” he wrote in an email.
“By ‘game over for the climate’, I mean game over for stabilizing warming below dangerous (ie greater than 2C) levels.
“If Trump makes good on his promises, and the US pulls out of the Paris [climate] treaty, it is difficult to see a path forward to keeping warming below those levels.”
Greenpeace UK said the new research was further evidence that urgent action was needed.
Dr Doug Parr, the environmental campaign group’s chief scientist, said: “The worrying thing is the suggestion climate sensitivity is higher [than thought] is not incompatible with higher temperatures we have been seeing this year.
“If there is science backing that up, that there’s a higher sensitivity of the climate to greenhouse gases, that puts at risk the prospect of keeping the globe at the Paris target of well below 2C.
“Anybody who understands the situation we find ourselves in would have already have realised we are in an emergency situation.”
Dr Tobias Friedrich, one of the authors of the paper, said: “Our results imply that the Earth’s sensitivity to variations in atmospheric carbon dioxide increases as the climate warms.
“Currently, our planet is in a warm phase – an interglacial period – and the associated increased climate sensitivity needs to be taken into account for future projections of warming induced by human activities.
“The only way out is to reduce greenhouse gas emissions as soon as possible.”
Dr Andrey Ganopolski, who was involved in the research and on the IPCC’s latest report, admitted their work was controversial with some scientists disagreeing and others agreeing with their findings.
“In our field of science, you cannot be definite by 100 per cent. There are always uncertainties and we discuss this in the paper,” he said.
“If we have more and more results of this sort, then we have more reasons to be concerned.”
Dr Ganopolski, of the Potsdam Institute for Climate Impact Research in Germany, suggested their findings meant it would be harder to prevent the world entering dangerous global warming of 2C or above.
“Our results mean it is not impossible to stay within 2C but it probably – if we are right and climate sensitivity is higher than this – would require even strong cuts in carbon emissions,” he said.
“Whether it’s feasible politically … I believe it is feasible technically.
“It would be really good to stay below 1.5C or close to that, whether it’s feasible I’m probably a bit sceptical about that.”
Commenting on the paper, Professor Eric Wolff, of Cambridge University, said using data from the past was a “powerful way of understanding the climate”.
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But he noted the authors had used different ways of estimating average global temperature, some of which had produced “a lower range of values”.
“The estimates of temperature in this paper are subject to large uncertainties, and therefore the range of estimates for 2100 is also very wide,” Professor Wolff said.
“Still, it’s encouraging that it overlaps with model estimates and confirms that the emission reductions promised in Paris are essential to avoid unacceptable climate changes.”
Mark Lynas laid out what would happen as the temperature rises in his award-winning book, Six Degrees: Our Future on a Hotter Planet.
He was shocked by the researchers’ results.
“It sounds on the apocalyptic side of bad and, in some ways, it is realistic because ‘business as usual’ just got more likely as Trump wants to rebuild the pipelines … the complete ‘fossilisation’ of the US,” he said.
“It was game over at six [degrees] to be honest. I don’t think there was much more to add, other than turning the planet into Venus.”
Nasa recently said Venus may once have been habitable before runaway global warming turned the planet into its current version of hell with temperatures of more than 460C, almost no water and an atmosphere of mainly carbon dioxide with clouds of sulphuric acid.