Climate Etc readers will be delighted to learn that Alexander Bakker’s thesis — which questions the scientific primacy of numerical general circulation models (GCMs) — has found strong support from James Hansen and a long list of collaborators, who represent strong climate-research groups from around the world!
An Old Story, but Useful Lessons
James Hansen, 26 September 2013
Introduction International discussions of human-made climate change (e.g., IPCC) rely heavily on global climate models, with less emphasis on inferences from the paleo record. A proper thing to say is that paleoclimate data and global modeling need to go hand in hand to develop best understanding — almost everyone will agree with that. […]
There is a tendency in the literature to treat an ensemble of model runs as if its distribution function is a distribution function for the truth, i.e., for the real world.
Wow. What a terrible misunderstanding.
Today’s models have many assumptions and likely many flaws in common, so varying the parameters in them does not give a probability distribution for the real world, yet that is often implicitly assumed to be the case. […]
Conclusion It is not an exaggeration to suggest, based on best available scientific evidence, that burning all fossil fuels could result in the planet being not only ice-free but human-free.
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Q&A with James Hansen
13 December, 2013
Our paper [“Assessing Dangerous Climate Change: Required Reductions of Carbon Emissions to Protect Young People, Future Generations and Nature”] is based fundamentally on observations, on studies of earth’s energy imbalance and the paleoclimate rather than on climate models.
Although I’ve spent decades working on [climate models], I think there probably will remain for a long time major uncertainties, because you just don’t know if you have all of the physics in there.
Some of it, like about clouds and aerosols, is just so hard that you can’t have very firm confidence.
So yes, while you could say most of these [messages] you can find one place or another, but we’ve put the whole story together. The idea was not that we were producing a really new finding but rather that we were making a persuasive case for the judge.
Please note the long list of coauthors associated to these strong statements: James Hansen, Pushker Kharecha, Makiko Sato, Valerie Masson-Delmotte, Frank Ackerman, David J. Beerling, Paul J. Hearty, Ove Hoegh-Guldberg, Shi-Ling Hsu, Camille Parmesan, Johan Rockstrom, Eelco J. Rohling, Jeffrey Sachs, Pete Smith, Konrad Steffen, Lise Van Susteren16, Karina von Schuckmann, James C. Zachos.
And Naomi Oreskes too has long been a critic of over-reliance upon complex numerical models:
Naomi “Merchants of Doubt” Oreskes
Slams “Corrosive” Climate Change Skepticism
Our 1994 paper in the journal Science [“Verification, Validation, and Confirmation of Numerical Models in the Earth Sciences”] took a critical look at numerical simulation models.
It’s never been my view that we should trust science uncritically. I’ve always been interested in the questions: How do we know when to trust science? How do we distinguish between healthy and corrosive skepticism? In short, how do we judge scientific claims?
In climate science, the case for the reality of anthropogenic climate change does not rest solely (or even primarily) on climate models. If it did, I’d be a skeptic too.
I still believe what I wrote in 1994: models are a tool for exploring and testing systems. Their primary value is heuristic. But together with other lines of evidence they can be part of a persuasive scientific case. Or not.
Conclusion General circulation models (GCMs) are not presently, and never have been, generally regarded as providing the strongest scientific evidence for the accelerating reality and harmful consequences of anthropogenic global warming (AGW).
To assert otherwise is — as Bakker, Hansen, and Oreskes all emphasize — “a terrible misunderstanding.”
Good on `yah Alexander Bakker … for joining James Hansen and Naomi Oreskes in publicly proclaiming this common-sense scientific reality!