PARIS • Greenhouse gases polluting the atmosphere from burning fossil fuels are warming Earth's surface more quickly than previously understood, according to new computer climate models set to replace those used in current UN projections, scientists said yesterday.
By 2100, average temperatures could rise 6.5 to 7 deg C above pre-industrial levels if carbon emissions continue unabated, separate models from two leading research centres in France showed.
That is up to 2 degrees higher than the equivalent scenario in the Intergovernmental Panel for Climate Change's (IPCC) 2014 benchmark 5th Assessment Report.
The new calculations also suggest the goals of the 2015 UN Paris Climate Agreement of capping global warming at "well below" 2 deg C, and 1.5 deg C if possible, will be harder to reach, the scientists said.
"With our two models, we see that the scenario known as SSP1 2.6 - which normally allows us to stay under 2C (2 deg C) - doesn't quite get us there," said Dr Olivier Boucher, head of the Institut Pierre Simon Laplace Climate Modelling Centre in Paris.
With barely 1 deg C of warming so far, the world is already suffering increasingly deadly heatwaves, droughts, floods and tropical cyclones made more destructive by rising sea levels.
A new generation of about 30 climate models known collectively as CMIP6 - including the two unveiled yesterday - will underpin the IPCC's next major climate assessment in 2021.
"CMIP6 clearly includes the latest modelling improvements", even as important uncertainties remain, said Imperial College London's associate professor Joeri Rogelj, a lead author of the IPCC report.
These improvements include increased supercomputing power and sharper representations of weather systems, natural and man-made particles, and how clouds evolve in a warming world. "We have better models now," said Dr Boucher.
"They have better resolution, and they represent current climate trends more accurately."
A core finding of the new models is that increased levels of carbon dioxide (CO2) in the atmosphere will warm earth's surface more easily than earlier calculations had suggested. CO2 is the main greenhouse gas from industry, transport, power generation and forest fires.
If confirmed, this higher "equilibrium climate sensitivity", or ECS, means humanity's carbon budget - our total emissions allowance - is likely to shrink.
"A higher ECS means a greater likelihood of reaching higher levels of global warming, even with deeper emissions cuts," Dr Boucher and two scientists - Dr Stephen Belcher from the UK Met Office and Dr Rowan Sutton from the UK National Centre for Atmospheric Science - wrote in a blog earlier this year. "Higher warming would allow less time to adapt and mean a greater likelihood of passing climate 'tipping points' such as thawing of permafrost, which would further accelerate warming."
A third to 99 per cent of top-layer permafrost could melt by 2100 if carbon pollution is not abated, releasing billions of tonnes of greenhouse gases into the air, according to a draft IPCC special report on oceans and earth's frozen zones obtained by Agence France-Presse.
"...what we need to do to keep warming to safe levels is extremely simple," said Dr Rogelj. "Global greenhouse gas emissions need to decline today rather than tomorrow, and global CO2 emissions should be brought to net zero."
AGENCE FRANCE-PRESSE
- This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.
