In this series on studies that estimate climate sensitivity based on observed climate data rather than climate models, we’ve noted how they usually come out at 2° C or less. And this week’s entry is definitely in the “or less” category. Ray Bates, the just-deceased former mathematician in the Meteorology and Climate Centre of the School of Mathematics and Statistics, University College Dublin, wrote a 2016 paper noting that many of the observation-based ECS estimates are based on using something called a zero-dimensional Energy Balance Model, where everything is reduced to global averages. What if, he asked, we add a bit of spatial detail by modeling the energy balance in the tropics and the extra-tropics independently, and allow heat to be transferred between them sort of like what happens in the real world? The answer is that the estimated ECS drops further from around 2° C to around 1° C.
Bates points out that this outcome was first discovered by MIT climatologist Richard Lindzen and his coauthors more than 20 years ago. In a series of papers they argued that ECS is controlled by the efficiency of the upper atmosphere at expelling heat to space, which is much higher in the tropics than elsewhere, so if the different zones are assumed to expel heat independently and the energy balance model is run using parameters estimated on observed data (that again) instead of model-generated numbers, the global ECS value drops to around 1° C. But, Bates points out, people in the climate field dismissed this finding because it was so different from models and because people thought there were problems in the way heat was transferred in the 2-zone model Lindzen was using.
Setting aside the first objection as circular reasoning, Bates set out to address the second. He took the basic model proposed by Lindzen and added an improved scheme for heat transfer across the zones. He then found updated data to set the parameter values for the calculations and after crunching the numbers estimated ECS to be somewhere in the range of 0.85° to 1.28° C.
So while we’ve been pointing out in this series that the usual IPCC assumption that ECS is around 3° C and could be as high as 5°C is wrong because real world data says it’s likely closer to 2° C, we’ve now got evidence it might be even lower still. And since an ECS of 2° C implies climate change is not a problem, an ECS of 1° C makes it even harder to justify incurring any costs trying to stop it, let alone scaring young people into suicidal depression over the coming apocalypse due to “carbon pollution”.