A new study by Italian physicist Nicola Scaffeta takes a new look at an old issue, namely are the IPCC models too hot? He begins by noting that the IPCC currently uses 41 climate models with the rise in absolute temperature due to doubling atmospheric CO2 (known in the trade as “Equilibrium Climate Sensitivity” or ECS) ranging from 1.8 to 5.7 °C. So let’s just pause right there and reflect that in the “settled science” of climate change the models currently being used by the IPCC differ in their projected warming response to CO2 emissions by more than a factor of three. Which seems like a lot. At the high end, if atmospheric CO2 doubles it could cause almost 6°C of warming, which would be a big problem for the world. At the low end it would cause 1.8°C, which would barely even be noticeable. So the IPCC models say CO2 emissions pose either no problem or a big problem or somewhere in between. If that’s settled science, what would the unsettled kind look like? But Scaffeta has now moved things towards a more genuinely settled state by asking which of the 41 models did better over the past 40 years by comparison with that grubby real-world data. The answer is, the ones with the lowest ECS values. And if we say the projections for the future should come from the models that have done the best over the past, the global warming picture suddenly looks a lot less heated.
Scaffeta’s results are summed up in this Figure:
On the bottom axis is the ECS programmed into the various models and on the vertical axis is the projected temperature change from the 1980s to the past decade. For each model there are four dots with the colours referring to the emission scenario considered, although since they all refer to warming over the past and the emissions were observed, they are all reasonably close together (the variations are due to internal variability in the models, not in the historical emission estimates). The cyan lines outline the range of observed temperature changes in the surface climate data (T2m) and the weather satellite data (ST).
It is clear at a glance that the observed warming rates are down at the bottom of the model warming range. Even the mid-range of models gets too hot too quickly, and certainly the high end are laughable.
Or they would be laughable if people had a proper sense of perspective about these things. But instead of laughter we get wailing and gnashing of teeth and declarations of a climate emergency based on overheated models.
Scafetta goes on to show that the models that got the past more accurate are the ones with lower ECS estimates, which are also therefore the ones that predict the least warming in the future. Based on his analysis, if the surface temperature data is accurate there are 17 models that could still be considered useful. But if the satellite-based data is considered the most accurate there is only one model that can claim to fit the data, and it has nearly the lowest of all.
Overall, Scafetta hints at the policy implications of his findings:
“As a result, the global aggregated impact and risk estimates seem to be moderate, which implies that any negative effects of future climate change may be adequately addressed by adaptation programs.”
In other words, chill out, we will adapt and cope with the small warming predicted by the best models. The real threat isn’t climate change, it’s climate policy.