Hopes that the rise in average global temperatures by 2100 might be capped below 2.5-degree Celsius can be all but ruled out if greenhouse gas emissions continue at the current rate, new research reassessing the atmosphere's sensitivity to carbon dioxide(CO2) suggests.
The study, under the Geneva-based World Climate Research Program, offers the first clear progress in decades toward narrowing the range of temperature rise caused by doubling of carbon dioxide levels since pre-industrial times.
Its findings show that doubling would trigger 2.6 to 4.1 degrees Celsius in average warming above pre-industrial levels, putting the lowest rise more than one degree above scientists' previous estimated range of 1.5-4.5-degree Celsius.
"To put that in perspective, we're on track to double CO2 at our current rate of emissions by around 2080," said co-author Zeke Hausfather, a climate scientist at the Breakthrough Institute research center in Oakland, Calif.
"Climate change is about as bad as we thought it was."
The scientific consensus that the goal of capping the rise in average global temperatures at 1.5-degree Celsius, as enshrined in the 2015 Paris climate accords, is almost certainly out of reach unless greenhouse gas emissions rates fall.
Known as the climate sensitivity parameter, a doubling of CO2 concentrations has been a mainstay of models for future global temperature since the late 1970s.
The study, published Wednesday in the journal Reviews of Geophysics, relied on computer simulations using satellite observations, historic temperature records, and evidence of prehistoric temperatures from sources such as tree rings.
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