Originally published on ThinkProgress.
By Joe Romm.
A major new study in Nature finds “our climate is more sensitive to carbon dioxide than most previous estimates.”
The result, lead author Steven Sherwood told me, is that on our current emissions path we are headed toward a “most-likely warming of roughly 5°C [9°F] above modern [i.e. current] temperatures or 6°C [11°F] above preindustrial” temperatures this century.
This finding is consistent with paleoclimate data (see “Last Time CO2 Levels Hit 400 Parts Per Million The Arctic Was 14°F Warmer!”). Also, this study is consistent with other recent observation-based analyses (see “Observations Support Predictions Of Extreme Warming And Worse Droughts This Century”).
This analysis throws more cold water (hot water?) on some recent claims that the climate’s sensitivity is on the low side, claims that have been widely challenged and perhaps fatally undermined by other recent studies.
Prof. Sherwood, from the University of New South Wales’ Centre of Excellence for Climate System Science, explains in the news release:
“Our research has shown climate models indicating a low temperature response to a doubling of carbon dioxide from pre-industrial times are not reproducing the correct processes that lead to cloud formation.”
“When the processes are correct in the climate models the level of climate sensitivity is far higher. Previously estimates of the sensitivity of global temperature to a doubling of carbon dioxide ranged from 1.5°C to 5°C. This new research takes away the lower end of climate sensitivity estimates, meaning that global average temperatures will increase by 3°C to 5°C with a doubling of carbon dioxide.”
Unfortunately, on our current path of unrestricted carbon pollution, we are headed well past a doubling (which would take us to 550 parts per million of CO2 in the air) this century. We’re headed towards a tripling (820 ppm) or quadrupling (1100 ppm) of atmospheric CO2 levels.
Sherwood told me “the model equilibrium climate sensitivity (ECS) most consistent with observations appeared to be around 4°C [7°F].” The “good news” is that inherent delays in the climate system mean we don’t hit the ECS immediately upon doubling. The “bad news” is that the ECS ignores key non-equilibrium feedbacks like the release of carbon currently locked in the frozen tundra (see “Carbon Feedback From Thawing Permafrost Will Likely Add 0.4°F – 1.5°F To Total Global Warming By 2100“).
Sherwood has an excellent video explaining his paper:
As Sherwood says, “Rises in global average temperatures of this magnitude will have profound impacts on the world and the economies of many countries if we don’t urgently start to curb our emissions.”
The full study can be found in the journal Nature (subs. req’d).
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