Earth coming to boil fasterWorld | AGENCE FRANCE-PRESSE 18 Sep 2019
Greenhouse gases thrust into the atmosphere by burning fossil fuels are warming Earth's surface more quickly than reckoned.
By 2100, average temperatures could rise 6.5 to 7.0 degrees Celsius above pre-industrial levels if carbon emissions continue unabated, separate models from two leading research centers in France show.
That is up to two degrees higher than the scenario in the Intergovernmental Panel for Climate Change's 2014 benchmark assessment report.
The new calculations also suggest the Paris Agreement goals of capping warming at "well below" two degrees - 1.5 degrees if possible - will be harder to reach.
"With our two models we see that the scenario known as SSP1 2.6, which normally allows us to stay under two degrees - doesn't quite get us there," said Olivier Boucher, head of the Institute Pierre Simon Laplace Climate Modelling Center.
With barely one degree of warming so far, the world is having to cope with increasingly deadly heat waves, droughts, floods and tropical cyclones made more destructive by rising seas.
A new generation of 30-odd climate models known collectively as CMIP6, including the two new ones, will underpin the IPCC's next major report in 2021.
Joeri Rogelj, an associate professor at Imperial College London and an IPCC lead author, said "CMIP6 clearly includes the latest modelling improvements" even as important uncertainties remain.
These include increased super-computing power and sharper representations of weather systems, natural and man-made particles, and how clouds evolve in a warming world.
A core finding of the new models is that increased levels of carbon dioxide in the atmosphere will warm Earth's surface more easily than earlier calculations suggested.
If confirmed, this higher "equilibrium climate sensitivity" means humanity's carbon budget - our total emissions allowance - is set to shrink. The French models are among the first to be released, but others developed independently reached the same unsettling conclusion, Boucher said.
This is bad news for fight against global warming, which continues to face strong political headwinds and institutional inertia.
And from 33 to 99 percent of permafrost could melt by 2100 if carbon pollution is not abated, releasing billions of tonnes of greenhouse gases into the air, a special IPCC report on oceans and Earth's frozen zones shows.