Apocalyptic predictions about the impact of climate change are ‘overstated’, according to a new study.
Experts have found that the UN’s worst case scenario, that the world could warm by up to 6°C (10.8°F) by 2100, is unlikely to happen.
New calculations worked out the probable impact of greenhouse gases on global warming and found that more extreme scenarios will almost certainly not occur.
They reduce the range of possible end-of-century outcomes by more than half, researchers said, including the best and worst case scenarios.
The findings suggest that the Paris Agreement on climate change, which seeks to limit temperature increases to below 2°C, is more achievable than some claim.
Apocalyptic predictions about the effects of climate change are overstated, according to a new study. Experts have found that the UN’s worst case scenario, that the world could warm by up to 6°C by 2100, is unlikely to happen.
Researchers from the University of Exeter used a new modelling method to examine how much the Earth’s average surface temperature will go up if the amount of CO2 in the atmosphere is doubled.
How effectively the world slashes CO2 and methane emissions, improves energy efficiency, and develops technologies to remove CO2 from the air will all determine whether climate change remains manageable or unleashes a maelstrom of misery.
But uncertainty about how hot things will get also stems from the inability of scientists to answer this simple question.
This ‘known unknown’ variable is called equilibrium climate sensitivity.
For the last 25 years, the UN’s Intergovernmental Panel on Climate Change (IPCC), the ultimate authority on climate science, has settled on a range of 1.5°C to 4.5°C (2.7°F to 8.1°F).
The Exeter team came up with a far narrower range of 2.2°C (3.9°F) to 3.4°C (6.1°F), with a best estimate of 2.8°C (5°F).
If accurate, it precludes the most destructive doomsday scenarios.
Lead author Peter Cox said: ‘Our study all but rules out very low and very high climate sensitivities.’
The landmark Paris climate agreement in 2015 called for capping global warming at ‘well under’ 2°C (3.6°F) compared to a pre-industrial benchmark, and pursuing efforts for a 1.5°C (2.7°F) ceiling.
The findings should not been seen as taking pressure off the need to tackle climate change, the authors and other experts warned.
Even a 1.5°C (2.7°F) increase will have consequences.
A 3.5°C (6.3°F) world, scientists say, could pull at the fabric of civilisation.
With a 1°C (1.8°F) of warming so far, the Earth is already coping with a crescendo of climate impacts including deadly droughts, erratic rainfall, and storm surges engorged by rising seas.
Piers Forster, director of the Priestley International Centre for Climate at the University of Leeds, who was not involved in the study, said: ‘These scientists have produced a more accurate estimate of how the planet will respond to increasing CO2 levels.
Researchers from the University of Exeter used a new modelling method to examine how much the Earth’s average surface temperature go up if the amount of CO2 in the atmosphere is doubled. The Thwaites glacier (pictured) is sliding into the ocean due to climate change
‘We will still see significant warming and impacts this century if we don’t increase our ambition to reduce CO2 emissions.’
Gabi Hegerl, a climate scientist at the University of Edinburgh who also did not take part in the research, added: ‘Having lower probability for very high sensitivity is reassuring.
‘Very high sensitivity would have made it extremely hard to limit climate change according to the Paris targets.’
Since industrialisation took off in the early 19th century, CO2 concentrations in the atmosphere have increased by nearly half, from 280 parts per million to 407 parts per million.
Up to now, attempts to narrow down the elusive equilibrium climate sensitivity have focused on the historical temperature record.
Processor Cox and colleagues instead ‘considered the year-to-year fluctuations in global temperature,’ said Richard Allan, a climate scientist at the University of Reading.
By analysing the responsiveness of short-term changes in temperature to ‘nudges and bumps’ in the climate system regardless of greenhouse gas emissions, he explained, they were able to exclude the outcomes that would have resulted in devastating increases of 4°C or more by 2100.
‘You might imagine the most obvious thing to do to get an idea of future climate change is to look at climate change to date,’ Cox told Wired.
‘But it turns out that’s a really poor constraint on the equilibrium climate sensitivity, and it’s basically because we don’t really know how much extra heat we’ve put in the system.’
One wild card not taken into consideration by the new model is the possibility of rapid shifts in climate brought on by the planet itself.
‘There is indeed evidence that the climate system can undergo abrupt changes or ‘tipping points’,’ Professor Cox told AFP.
The collapse of the gulf stream, the thawing of carbon-rich permafrost, or the melting of ice sheets on Greenland and Antarctica – any of these could quickly change the equation and not in the Earth’s favour.
The full findings of the report were published in the journal Nature.