Climate Scientists Step Up the Climate Emergency Narrative

CMIP6 Climate Sensitivities. Source Carbon Brief

Guest essay by Eric Worrall

Even worse than we thought ™. Despite a recent sanity test study which demonstrated that high end climate models hindcast impossible Eocene temperatures, climate scientists are pushing ahead anyway with their new, even more extreme climate projections.

Climate worst-case scenarios may not go far enough, cloud data shows

Modelling suggests climate is considerably more sensitive to carbon emissions than thought

Jonathan Watts @jonathanwatts
Sat 13 Jun 2020 16.00 AEST

Modelling results from more than 20 institutions are being compiled for the sixth assessment by the United Nations Intergovernmental Panel on Climate Change, which is due to be released next year.

Compared with the last assessment in 2014, 25% of them show a sharp upward shift from 3C to 5C in climate sensitivity – the amount of warming projected from a doubling of atmospheric carbon dioxide from the preindustrial level of 280 parts per million. This has shocked many veteran observers, because assumptions about climate sensitivity have been relatively unchanged since the 1980s.

“That is a very deep concern,” Johan Rockström, the director of the Potsdam Institute for Climate Impact Research, said. “Climate sensitivity is the holy grail of climate science. It is the prime indicator of climate risk. For 40 years, it has been around 3C. Now, we are suddenly starting to see big climate models on the best supercomputers showing things could be worse than we thought.”Advertisement

Timothy Palmer, a professor in climate physics at Oxford University and a member of the Met Office’s advisory board, said the high figure initially made scientists nervous. “It was way outside previous estimates. People asked whether there was a bug in the code,” he said. “But it boiled down to relatively small changes in the way clouds are represented in the models.”

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A month ago WUWT reported a study which demonstrated the new high end climate sensitivity projections (specifically CESM2) are incompatible with the fossil record.

CESM2, one of the new models, hindcasts tropical temperatures in excess of 55C during the early Eocene, temperatures which would have made photosynthesis impossible, creating lifeless tropical deserts.

The fossil record says different; the early Eocene was a period of abundant tropical life. 

Some of the newest models used to make future predictions may be too sensitive to increases in atmospheric carbon dioxide and thus predict too much warming,” said U-M’s Chris Poulsen, a professor in the U-M Department of Earth and Environmental Sciences and one of the study’s three authors. – source Science Daily

Poulsen’s team are not climate skeptics. They suggested CESM1.2, the predecessor of CESM2, did a “remarkably good job” of simulating early Eocene temperatures. CESM1.2 has an equilibrium climate sensitivity of 4.2C (7.6F), vs 5.2C (9.3F) for CESM2.


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