Is more computing power just getting us the wrong results from overheated models faster?
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Outside of their academic fascination, looked at in terms of their contribution to climate policy, it seems that we may have reached the useful limit of computer climate modelling, says Dr. David Whitehouse.
The first computers built in the 1950s allowed climate scientists to think about modelling the climate using this new technology.
The first usable computer climate models were developed in the mid-1970s.
Shortly afterwards the US National Academy of Sciences used their outcomes to estimate a crucial climate parameter we still calculate today – the Equilibrium Climate Sensitivity (ECS) – how much the world would warm (from ‘pre-industrial’ levels) with a doubling of CO2 — and concluded that it had a range of 1.5 – 4.5°C.
Since then computer power has increased by a factor of more than a quadrillion yet, one could argue, climate models have not much improved on that original estimate. Their range of projections has not narrowed significantly, and consequently the contribution they make to climate policy hasn’t improved concomitantly.
From the time of the IPCC’s AR1 (1990) all the way to AR4 (2007) it was 2.0 – 4.5°C. AR5 (2015) changed it only slightly to 1.9 – 4.5°C. Significantly, the most recent IPCC assessment, AR6 (2021), took a step back partially decoupling computer models and model predictions, replacing them with “expert judgement” of ECS that gave more emphasis on other sources of information.
AR6 did not consider all climate models to be equal and weighted them according to their hindcast abilities. Subsequently AR6 narrowed the ECS range to 2.5 – 4.0°C. This can hardly been regarded as real improvement.
At the time climate scientists were looking forward to new rounds of computer modelling, particularly the so-called Coupled Model Intercomparison Project (CMIP6) effort to reduce the ECS uncertainty. But it was clear very early on that the opposite was happening, uncertainty was actually increasing.
CMIP6 eventually concluded that ECS was 2.0 – 5.5°C. The fact that CMIP6 has too many climate models running too hot is telling us something important. The model democracy of the past, which we at the GWPF and others were criticised for pointing out, was indeed wrong.
In summary, not many climate models concurred with reality leading to suggestions that only those that did should be considered useful. Instead many studies encompassed all the models, including the ones that did not reproduce observations, and used the median of them all, and their spread, as a way to predict future climate change.
It was always an inconvenience that nature was not following the median of the models, and an irritation that “sceptics” pointed out that it was unscientific not to discard models that did not fit real-world data.
Full article here.
via Tallbloke’s Talkshop
June 11, 2022 at 03:15AM