Archives par mot-clé : ECS

Modern Climate Change Science

by A. May, Nov 12, 2020 in WUWT

The first modern theoretical estimates of ECS were reported in 1979 in the so-called “Charney Report” (Charney, et al., 1979). They reported, on page 2, a theoretical ECS of 1.5°C to 4.5°C per doubling of the CO2 atmospheric concentration. This estimate included an estimate of water vapor feedbacks, the effect of ice and their assumed uncertainties. Absent any water vapor feedback their computed value was 1°C per doubling of CO2. They also supply a likely value of 2.4°C on page 9, although on page 2 they offer a value “near 3.0.” The page 9 value is not far off from the empirical estimate of 2°C made by Guy Callendar in 1938, but significantly higher than the 1.2°C to 1.95°C (17% to 83% range, best estimate 1.5°C) given by Nic Lewis and Judith Curry (Lewis & Curry, 2018).

The IPCC, in their AR5 report (Bindoff & Stott, 2013), estimate ECS as lying between 1.5°C and 4.5°C and provide no best estimate. This range is precisely the same as the Charney Report made 34 years earlier. While the empirical, observation-based, estimates have narrowed significantly, the theoretical range has not changed, despite thousands of government-funded scientists spending billions of dollars trying to do so. The data is very much the same today and churning it faster with more powerful computers and billions of dollars doesn’t seem to matter. It works the same way with manure.

Digging deeply into the AR5 internals, as Monckton, et al. did in MSLB15, a paper entitled, “Why Models run hot: results from an irreducibly simple climate model” (Monckton, Soon, Legates, & Briggs, 2015), we see that the elements of the AR5 theoretical calculations suggest that the range is narrowing in a downward direction. Given the political environment at the IPCC, one can easily suspect that the politicians do not want to admit the theoretical risks of CO2-caused climate change are lessening. As more empirical estimates of the CO2 effect appear and more theoretical work is done, one wonders how long the politicians can support the clearly inflated range of 1.5°C to 4.5°C?

Estimates of ECS have been declining for a long time, as shown in 2017 by Nicola Scafetta and colleagues. Figure 1 is from their paper:

The decline in estimates of ECS from 2000 to 2015. Source: Scafetta, Mirandola, and Bianchini, 2017.

Climate Models Have Not Improved in 50 Years

by David Middleton, December 6, 2019 in WUWT

The accuracy of the failed models improved when they adjusted them to fit the observations… Shocking.

The AGU and Wiley currently allow limited access to Hausfather et al., 2019. Of particular note are figures 2 and 3. I won’t post the images here due to the fact that it is a protected limited access document.

Figure 2: Model Failure

Figure 2 has two panels. The upper panel depicts comparisons of the rates of temperature change of the observations vs the models, with error bars that presumably represent 2σ (2 standard deviations). According to my Mark I Eyeball Analysis, of the 17 model scenarios depicted, 6 were above the observations’ 2σ (off the chart too much warming), 4 were near the top of the observations’ 2σ (too much warming), 2 were below the observations’ 2σ (off the chart too little warming), 2 were near the bottom of the observations’ 2σ (too little warming), and 3 were within 1σ (in the ballpark) of the observations.

Figure 2. Equilibrium climate sensitivity (ECS) and transient climate response

What’s the worst case? Climate sensitivity

by Judith Curry, April 1, 2019 in WUWT

Are values of equilibrium climate sensitivity > 4.5 C plausible?

For background, see these previous posts on climate sensitivity [link]

Here are some possibilistic arguments related to climate sensitivity.  I don’t think the ECS example is the best one to illustrate these ideas [see previous post], and I probably won’t include this example in anything I try to publish on this topic (my draft paper is getting too long anyways).  But possibilistic thinking does point you in some different directions when pondering the upper bound of plausible ECS values.

5. Climate sensitivity

Equilibrium climate sensitivity (ECS) is defined as the amount of temperature change in response to a doubling of atmospheric CO2 concentrations, after the climate system has reached equilibrium. The issue with regards to ECS is not scenario discovery; rather, the challenge is to clarify the upper bounds of possible and plausible worst cases.

The IPCC assessments of ECS have focused on a ‘likely’ (> 66% probability) range, which has mostly been unchanged since Charney et al. (1979), to be between 1.5 and 4.5 oC. The IPCC AR4 (2007) did not provide any insight into a worst-case value of ECS, stating that values substantially higher than 4.5 oC cannot be excluded, with tail values in Figure 9.20 exceeding 10 oC. The IPCC AR5 (2013) more clearly defined the upper range, with a 10% probability of exceeding 6 oC.

Since the IPCC AR5, there has been considerable debate as to whether ECS is on the lower end of the likely range (e.g., < 3 oC) or the higher end of the likely range (for a summary, see Lewis and Curry, 2018). The analysis here bypasses that particular debate and focuses on the upper extreme values of ECS.