Guest essay by Eric Worrall

University of Michigan researchers have done the unthinkable, and checked climate model predictions against available paleo-climate data to see if the predictions are plausible.

Some of the latest climate models provide unrealistically high projections of future warming

Date:April 30, 2020Source:University of MichiganSummary:A new study from climate researchers concludes that some of the latest-generation climate models may be overly sensitive to carbon dioxide increases and therefore project future warming that is unrealistically high.

A new study from University of Michigan climate researchers concludes that some of the latest-generation climate models may be overly sensitive to carbon dioxide increases and therefore project future warming that is unrealistically high.

In a letter scheduled for publication April 30 in the journal Nature Climate Change, the researchers say that projections from one of the leading models, known as CESM2, are not supported by geological evidence from a previous warming period roughly 50 million years ago.

The researchers used the CESM2 model to simulate temperatures during the Early Eocene, a time when rainforests thrived in the tropics of the New World, according to fossil evidence.

But the CESM2 model projected Early Eocene land temperatures exceeding 55 degrees Celsius (131 F) in the tropics, which is much higher than the temperature tolerance of plant photosynthesis — conflicting with the fossil evidence. On average across the globe, the model projected surface temperatures at least 6 C (11 F) warmer than estimates based on geological evidence.

“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.

…

“Our study implies that CESM2’s climate sensitivity of 5.3 C is likely too high. This means that its prediction of future warming under a high-CO2 scenario would be too high as well,” said Zhu, first author of the Nature Climate Change letter.

…

Read more: https://www.sciencedaily.com/releases/2020/04/200430113003.htm

“People underestimate the power of models. Observational evidence is not very useful” – attributed to John Mitchell, UK MET

Most fields of science don’t accept a model unless it has been rigorously validated against available data, but climate science is different; the modelling process itself frequently seems to be accepted as evidence that the climate model is correct, a circular chain of reasoning which leads to positions which outside of climate science would be considered absurd.

Let us hope this novel protocol of testing climate models against available evidence catches on.

The paywalled study is available here.