Wednesday, April 06, 2022

More on inconsistent and warming biased climate models

Much of the propaganda and demagoguery of climate change is based on the forecasts of large climate models. 

It has been reported now many times that these large models are e.g. incapable of correctly backcasting the past.

The often cited comparison with preindustrial temperatures (1850-1900) is a joke, because of the Little Ice Age and growing world population!

By the way, we can still not forecast weather fairly accurately for more than 48 hours or so (weather and climate are related and both similarly complex).

"... there are about 40 major climate models and their climate sensitivity levels vary by a factor of three, from 1.8 to 5.7 degrees C per doubling of carbon dioxide. Which right away tells you there is a lot of guesswork going on. ..."

From the abstract:
"The equilibrium climate sensitivity (ECS) of the CMIP6 global circulation models (GCMs) varies from 1.83°C to 5.67°C. Herein, 38 GCMs are grouped into three ECS classes (low, 1.80–3.00°C; medium, 3.01–4.50°C; high, 4.51–6.00°C) and compared against the ERA5-T2m records from 1980–1990 to 2011–2021. We found that all models with ECS > 3.0°C overestimate the observed global surface warming and that spatial t-statistics rejects the data-model agreement over 60% (using low-ECS GCMs) to 81% (using high-ECS GCMs) of the Earth's surface. Thus, the high and medium-ECS GCMs are unfit for prediction purposes. The low-ECS GCMs are not fully satisfactory yet, but they are also found unalarming because by 2050 they predict a moderate warming (ΔTpreindustrial→2050 ≲ 2°C)."

From the plain language summary:
"Plain Language Summary
The last-generation Coupled Model Intercomparison Projects (CMIP6) global circulation models (GCMs) are used by scientists and policymakers to interpret past and future climatic changes and to determine appropriate (adaptation or mitigation) policies to optimally address scenario-related climate-change hazards. However, these models are affected by large uncertainties. For example, their equilibrium climate sensitivity (ECS) varies from 1.83°C to 5.67°C, which makes their 21st-century predicted warming levels very uncertain. This issue is here addressed by testing the GCMs' global and local performance in predicting the 1980–2021 warming rates against the ERA5-T2m records and by grouping them into three equilibrium climate sensitivity (ECS) classes (low-ECS, 1.80–3.00°C; medium-ECS, 3.01–4.50°C; high-ECS, 4.51–6.00°C). We found that: (a) all models with ECS > 3.0°C overestimate the observed global surface warming; (b) Student t-tests show model failure over 60% (low-ECS) to 81% (high-ECS) of the Earth's surface. Thus, the high and medium-ECS GCMs do not appear to be consistent with the observations and should not be used for implementing policies based on their scenario forecasts. The low-ECS GCMs perform better, although not optimally; however, they are also found unalarming because for the next decades they predict moderate warming: ΔTpreindustrial→2050 ≲ 2°C."

"... The large ECS [equilibrium climate sensitivity] uncertainty is due to the poor physical understanding of various feedback mechanisms such as water vapor and cloudiness ..."


Advanced Testing of Low, Medium, and High ECS CMIP6 GCM Simulations Versus ERA5‐T2m - Scafetta - 2022 - Geophysical Research Letters - Wiley Online Library

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