Archives par mot-clé : CO2 Sensivity

Climate Sensitivity to CO2, what do we know? Part 2.

by A. May, July 8, 2021 in WUWT


In Part 1, we introduced the concepts of climate sensitivity to CO2, often called ECS or TCR. The IPCC prefers a TCR of about 1.8°C/2xCO2 (IPCC, 2013, p. 818). TCR is the short-term, century scale, response of surface temperature to a doubling of CO2, we abbreviate the units as “°C/2xCO2.” In these posts we review lower estimates of climate sensitivity, estimates below 1°C/2xCO2. In parallel, we also review estimates of the surface air temperature sensitivity (SATS) to radiative forcing (RF, the units are °C per W/m2 or Watts per square meter). The IPCC estimates this value to be ~0.49°C per W/m2.

The previous post discussed two modern climate sensitivity estimates, by Richard Lindzen and Willie Soon, that range below 1°C/2xCO2. Next, we review climate sensitivity estimates by Sherwood Idso, Reginald Newell and their colleagues.

Many comments to part 1 tried to discredit the “ECS” or “TCR” estimates made by Lindzen and Soon, completely missing their point and my point. ECS and TCR are artificial climate model constructs, with little meaning outside the confines of computer modeling. TCR is a little more realistic since we might be able to observe or measure something close to it over the next century. But ECS, or the “Equilibrium Climate Sensitivity” is a totally abstract and unworldly number that could never be measured. It means if CO2 doubled suddenly, and nothing else changed for several hundred years while the oceans came into equilibrium with the new surface air temperature, what would the final surface temperature be? Air temperature would never be close to equilibrium for several hundred years, even 70 to 100 years (TCR) is a stretch.

Climate models are not the real world and the numbers that come out of them, like ECS or TCR, can be useful for showing the likely direction of temperature movement in response to changes in parameters or different model scenarios, but the numbers themselves are meaningless unless the models have previously been validated against the real world. With the possible exception of the Russian INM-CM4 model, no other IPCC model has successfully predicted future global surface temperatures. Ron Clutz discusses INM-CM4 here.

Model calculations are not observations. ECS and TCR are not real numbers, real numbers are based on observations. Thus, the model extracted values of ECS and TCR are not information, they can be used to detect the direction of change in climate forcing, if the climate model is an accurate reflection of that portion of the real world. The direction of movement of ECS and TCR, when model parameters or data tables change, is the information, not the computed value. I’m often amazed, as a former petrophysical modeler of 42 years, how often otherwise intelligent people confuse unvalidated model calculations with observations.

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.