From Dr. Judith Curry’s Climate, etc
by Frank Bosse
very interesting blog post by Gavin Schmidt provides input on the “limitation” of TCR (Transient Climate Response) observed between 1979-2022 using the latest climate models.
Gavin presents a comparison of their “TCR-screened models” with observations using GISS surface temperature data:
Figure 1: Copy of the first image in Gavin’s blog post.
What does Gavin mean when he says “The model is screened by TCR”? He mentioned Tokarska et al (2020). Tokarska et al used all CMIP6 (and CMIP5) models to constrain TCR using regression against observed warming. This is not exactly the method Gavin used. From the chapter “Constraints to TCR” by Tokarska (2020):
“We find that the recent warming trend (1981–2017) is strongly correlated with TCR on CMIP6 models (R = 0.82)”
This also means that the warming trend from 1979 to 2022 is more correlated with the TCR than the results found in Tokarska et al (2020) because of a longer time period: 44 versus 37 years.
The slope of the trend tells the story of the implied TCR.
Tokarska et al. describe the “observation-restricted TCR” as:
“Observationally restricted TCR range (17 to 83%), based on CMIP6 samples only, is 1.20° to 1.99°C with a mean of 1.60°C”
The best estimate of TCR based on CMIP6 samples (red line in Figure 1) is 1.6K/2*CO2, according to the cited paper.
Using preliminary GMST data from GISS for January – October 2022, I reconstructed Figure 1 from Gavin’s post to estimate the slope of the 1979-2022 warming trend:
Figure 2: Added GMST for 2022 and the slope of the OLS trend for Observation and “TCR-bound” CMIP6 models, digitized from Figure 1 in Gavin’s blog post.
The slope of the trend (“strong correlation with TCR“, as stated by Tokarska et al.) is different, observations (GISS) show that the slope of the trend is 21% lower than the models. CMIP6 is TCR-restricted, having a TCR of 1.6 as best estimate.
Considering this fact, the observations that a TCR of 1.6/1.21= 1.3 K/double CO2 is the best estimate. The possible range of 17 to 83% from the regression is 1.22 to 1.38.
These TCR values are very similar to estimates of Lewis/Curry (2018).
A TCR of 1.3, confirmed by the latest data, shows a warming by 2100 of 1.75 compared to pre-industrial times, when a 4.5 W/m² forced scenario is considered. We will remain within the “2°C target” even if the pressure is between 5W/m² and 2100, we will generate 1.9 K of temperature.
All existing serious literature rules out catastrophic consequences of global warming, if we stay within the 2K limit. It seems very likely that we will. No resignation and no glue on the streets and paintings. Someone should inform the frightened people are doing such strange things in the name of “Science”.
Science says the opposite, offering much hope that humanity will avoid the “final game of catastrophic climate”.
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