From Weather Underground (Bob Henson):
Our planet’s climate may be more sensitive to increases in greenhouse gas than we realized, according to a new generation of global climate models being used for the next major assessment from the Intergovernmental Panel on Climate Change (IPCC). The findings—which run counter to a 40-year consensus—are a troubling sign that future warming and related impacts could be even worse than expected.
One of the new models, the second version of the Community Earth System Model (CESM2) from the National Center for Atmospheric Research (NCAR), saw a 35% increase in its equilibrium climate sensitivity (ECS), the rise in global temperature one might expect as the atmosphere adjusts to an instantaneous doubling of atmospheric carbon dioxide. Instead of the model’s previous ECS of 4°C (7.2°F), the CESM2 now shows an ECS of 5.3°C (9.5°F).
“It is imperative that the community work in a multi-model context to understand how plausible such a high ECS is,” said NCAR’s Andrew Gettelman and coauthors in a paper published last month in Geophysical Research Letters. They added: “What scares us is not that the CESM2 ECS is wrong…but that it might be right.”
At least eight of the global-scale models used by IPCC are showing upward trends in climate sensitivity, according to climate researcher Joëlle Gergis, an IPCC lead author and a scientific advisor to Australia’s Climate Council. Gergis wrote about the disconcerting trends in an August column for the Australian website The Monthly.
Researchers are now evaluating the models to see whether the higher ECS values are model artifacts or correctly depict a more dire prognosis.
“The model runs aren’t all available yet, but when many of the most advanced models in the world are independently reproducing the same disturbing results, it’s hard not to worry,” said Gergis.