Archives par mot-clé : ECS

climate-debate

CMIP6 GCM Validation Based on ECS and TCR Ranking for 21st Century Temperature Projections and Risk Assessment

by N. Scafetta, Feb 9, 2023 in MDPI_Atmosphere

Abstract

Global climate models (GCMs) from the sixth Coupled Model Intercomparison Project Phases (CMIP6) have been employed to simulate the twenty-first-century temperatures for the risk assessment of future climate change. However, their transient climate response (TCR) ranges from 1.2 to 2.8 °C, whereas their equilibrium climate sensitivity (ECS) ranges from 1.8 to 5.7 °C, leading to large variations in the climatic impact of an anthropogenic increase in atmospheric CO2 levels. Moreover, there is growing evidence that many GCMs are running “too hot” and are hence unreliable for directing policies for future climate changes. Here, I rank 41 CMIP6 GCMs according to how successfully they hindcast the global surface warming between 1980 and 2021 using both their published ECS and TCR estimates. The sub-ensemble of GCMs with the best performance appears to be composed of the models with ECS ranging between 1.8 and 3.0 °C (which confirms previous studies) and TCR ranging between 1.2 and 1.8 °C. This GCM sub-ensemble is made up of a total of 17 models. Depending on the emission scenarios, these GCMs predict a 2045–2055 warming of 1.5–2.5 °C compared to the pre-industrial era (1850–1900). As a result, the global aggregated impact and risk estimates seem to be moderate, which implies that any negative effects of future climate change may be adequately addressed by adaptation programs. However, there are also doubts regarding the actual magnitude of global warming, which might be exaggerated because of urban heat contamination and other local non-climatic biases. A final section is dedicated to highlighting the divergences observed between the global surface temperature records and a number of alternative temperature reconstructions from lower troposphere satellite measurements, tree-ring-width chronologies, and surface temperature records based on rural stations alone. If the global warming reported by the climate records is overestimated, the real ECS and TCR may be significantly lower than what is produced by the CMIP6 GCMs, as some independent studies have already suggested, which would invalidate all of the CMIP6 GCMs.
better to know...?, climate-debate

Study Finds The CO2 Greenhouse Effect Is Real…But Dangerous Global Warming From Rising CO2 Is Not

by K. Richard, Nov 24, 2022 in NoTricksZone

German physicists claim to have experimentally demonstrated the greenhouse effect from greenhouse gases like CO2 and CH4 is a real phenomenon, but assess the climate sensitivity to a doubling of CO2 with feedbacks is “only ECS = 0.7°C … 5.4x lower than the mean value of CMIP6 with ECS = 3.78°C.”

“The derived forcing for CO2 is in quite good agreement with some theoretical studies in the literature, which to some degree is the result of calibrating the set-up to the spectral calculations, but independently it determines and also reproduces the whole progression as a function of the gas concentration. From this we deduce a basic equilibrium climate sensitivity (without feedbacks) of ECSB = 1.05°C. When additionally assuming a reduced wing absorption of the spectral lines due to a finite collision time of the molecules this further reduces the ECSB by 10% and, thus, is 20% smaller than recommended by CMIP6 with 1.22°C.”
“Detailed own investigations also show that in contrast to the assumptions of the IPCC water vapor only contributes to a marginal positive feedback and evaporation at the earth’s surface even leads to a significant further reduction of the climate sensitivity to only ECS = 0.7°C (Harde 2017 [15]). This is less than a quarter of the IPCC’s last specification with 3°C (see AR6 [1]) and even 5.4x lower than the mean value of CMIP6 with ECS = 3.78°C.”

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climate-debate

he IPCC’s Climate Math Doesn’t Add Up. Will Anyone Notice?

by R. McKitrick, Oct 14, 2022 in ClimateChangeDispatch

The high and rising costs of climate policy — now including the inability of jurisdictions that bet big on renewables to guarantee enough energy for their citizens to survive the coming winter — don’t just entitle us to question the basis for it: they demand we do so.

Ultimately, the justification for renewables is the view that carbon dioxide emissions have a big effect on the climate that will cause devastating harm at some point in the future. [bold, links added]

Scientists measure the effect using a concept called “Equilibrium Climate Sensitivity” or ECS, which estimates how much long-run average warming will occur as a result of doubling the amount of carbon dioxide in the atmosphere.

Some important new evidence pointing to a low ECS value just emerged in the scientific literature.

ECS has long been uncertain. In 1979 the U.S. National Academy of Sciences estimated it to be between 1.5 and 4.5 degrees Celsius, with a best estimate of 3.0 degrees C.

That range, which runs from “no big deal” to “very bad outcomes,” was accepted by the UN Intergovernmental Panel on Climate Change (IPCC) in its first report in 1990 and thereafter until 2007 when, citing greater warming projections in newer models, it raised the bottom end to 2.0 degrees C.

But over the next few years, literature developed using, not model simulations, but observed warming rates since the late-1800s to estimate ECS.

Its results typically centered around 2.0 C or less. So in 2013, the IPCC reduced the bottom end of the range back to 1.5 C and declined to offer a best estimate. In other words, after three decades climate science hadn’t narrowed the uncertainty at all.

The economic implications of ECS being 2 C rather than 3 C are enormous.

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climate-debate

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.
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climate-debate

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

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climate-debate

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.

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