From Tallbloke’s Talkshop

February 16, 2023 by oldbrew

Here we learn “our review revealed how surprisingly little we know about slow-moving climate variability”. In between unsupported assertions about human-caused modern warming, the authors of the review article ponder the realities of natural climate variability, including a warmer-than-today period in the Holocene, under the headings ‘What we know’, ‘What we don’t know’, and ‘Why it matters’. The closing line: “Our review suggests that climate models are underestimating important climate feedbacks that can amplify global warming.” Is this another way of saying long-term natural variation is being underestimated by the models?
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Accurate climate models play a critical role in climate science and policy, helping to inform policy- and decision-makers throughout the world as they consider ways to slow the deadly effects of a warming planet and to adapt to changes already in progress, says Eurekalert.

To test their accuracy, models are programmed to simulate past climate to see if they agree with the geologic evidence.

The model simulations can conflict with the evidence. How can we know which is correct?

A review article published today in Nature addresses this conflict between models and evidence, known as the Holocene global temperature conundrum.

Lead author Darrell Kaufman, a Regents’ professor in the School of Earth and Sustainability, and University of Arizona postdoctoral researcher Ellie Broadman, a co-author who worked on this study while earning her Ph.D. at NAU, analyzed a broad swath of available data from the last 12,000 years to break down the conundrum.

The study builds on work Kaufman did that was included in the latest major climate report by the Intergovernmental Panel on Climate Change (IPCC) and looks at whether the global average temperature 6,500 years ago was warmer, as indicated by proxy evidence from natural archives of past climate information, or colder, as simulated by models, in comparison to the late 19th century, when the Industrial Revolution led to a significant increase in human-caused warming.

This comprehensive assessment concludes that the global average temperature about 6,500 years ago was likely warmer and was followed by a multi-millennial cooling trend that ended in the 1800s. But, they cautioned, uncertainty still exists despite recent studies that claimed to have resolved the conundrum.

“Quantifying the average temperature of the earth during the past, when some places were warming while others were cooling, is challenging, and more research is needed to firmly resolve the conundrum,” Kaufman said. “But tracing changes in global average temperature is important because it’s the same metric used to gauge the march of human-caused warming and to identify internationally negotiated targets to limit it. In particular, our review revealed how surprisingly little we know about slow-moving climate variability, including forces now set into motion by humans that will play out as sea level rises and permafrost thaws over coming millennia.”

Full article here.