Equilibrium Doubled-CO2 Sensitivity by Observational Methods

By Christopher Monckton of Brenchley | Dec. 22, 2022

Dr Roy Spencer, in his formidable recent paper, has made perhaps the most comprehensive effort ever to evaluate all the available meteorological data and to derive therefrom an upper-bound estimate of <2.1 K equilibrium doubled-CO2 sensitivity (ECS). His method, like all the best methods, is based more on observational than on numerical techniques.

He concludes that 2.1 K is an upper bound because climatology has not taken sufficient account of subsurface warming from below (Professor Viterito has long suspected subocean volcanism as a significant contributor to recent warming), and has also made insufficient correction for the urban heat-island effect. Here, I compare Dr Spencer’s result with two other available observational methods.

Observational method 1: prediction vs. outturn

IPCC (1990), an early attempt by the international scientific community at constraining ECS. estimated it as 3 [1.5, 4.5] K. The interval has changed little: IPCC (2021) gave 3 [2, 5] K. IPCC’s original prediction from 1990, together with observed temperature change since then, provides the basis for perhaps the simplest observational method of deriving ECS.

Anthropogenic emissions since 1990 have proven closer to IPCC’s then business-as-usual scenario A than to B-D: for CO2 accounts for two-thirds of our sins of emission, and from 1990-2025 the scenario B CO2 prediction was near-identical to IPCC’s prediction based on the assumption that there would be no emissions growth after 1990. Yet in reality there has been considerable emissions growth since 1990. Scenario A, then, is closest to real emissions.

In the third of a century since 1990, the 0.3 K decade–1 midrange medium-term warming (10% of 3 K midrange ECS) predicted in scenario Ahas proven excessive by a factor 2. Observed warming from 1990-2022 was only 0.14 K decade–1 using Roy Spencer’s UAH database. On the Scenario A assumption that ECS is ten times the decadal warming rate, observationally-derived midrange ECS is just 1.4 K. Let us verify that result another way.

Observational method 2: the energy-budget method

The energy-budget method (Gregory 2004) is another simple observational method, which, in paper after paper (including Lewis & Curry 2018, cited by Roy Spencer), has produced lower ECS estimates than the models. The method permits direct derivation of ECS, subject to uncertainties in five initial conditions, whose midrange intervals are illustratively as follows:

Anthropogenic fraction M of industrial-era warming: Wu et al. (2019, table 2) give surface air temperature trends for eight periods of varying length from 1900-2013 and the anthropogenic CO2-equivalent and natural contributions summing thereto for each period. Apportionment by period length suggests M is equal to 73.5% of industrial-era warming. Here, the illustrative midrange interval of M is taken as 85% [70%, 100%].

Industrial-era observed transient warming ΔTEB, taken as the least-squares linear-regression trend on the monthly global mean surface temperature anomalies since 1850, is 1.04 K (HadCRUT5; cf. 0.93 K to 2020 in HadCRUT4). However, IPCC (2021, p. 7-9) gives 1.27 K. Here, the midrange interval of ΔTEB is taken as 1.1 [0.93, 1.27] K.

Doubled-CO2-equivalent anthropogenic forcing ΔQ1 is 3.93 W m–2 (IPCC, 2021 p. 7-7), cf. CMIP5 3.45 W m–2 in Andrews 2012; CMIP6 3.52 W m–2 in Zelinka et al. 2020). Here, the midrange interval is taken as 3.69 [3.45, 3.93] W m–2.

Anthropogenic net forcing ΔQEB to 2019was 2.84 W m–2 (IPCC 2021, table AIII.3). Adding 0.045 W m–2 yr–1 for each of the three years 2020-2022 (based on the recent near-linear trend in Butler & Montzka 2020) yields 3 W m–2 anthropogenic forcing ΔQEB to 2022. However, ΔQEB becomes 3.4 W m–2 after adding 0.4 W m–2 (e.g. Seifert et al. 2015, Stevens 2015, Fiedler et al. 2017, Lewis & Curry 2018, Sato et al. 2018, Dittus et al. 2020) for overstated negative aerosol forcing in GCMs. Here, the midrange interval is taken as 3.4 [3.2, 3.6] W m–2.

Earth energy imbalance ΔNEB is 0.79 W m–2 (IPCC 2021, p. 7-6, the mean of 0.87 W m–2 (von Schuckmann et al. 2020) and 0.71 W m–2 (Raghuraman et al. 2021). The interval of midrange ΔNEB is thus 0.79 [0.71, 0.87] W m–2.

The following equation gives midrange energy-budget ECS (ΔE1)EB. Monte Carlo simulation (109 trials) gives the 2σ interval of midrange ECS as 1.3 [1.0, 1.7] K (Fig. 2), cohering with the observational 1.4 ECS derived earlier, but well below the hitherto-projected 3 K.

Eq. (1) assumes that the realized fraction of observed industrial-era warming was driven by the realized forcing (i.e., the difference between the total period anthropogenic forcing and the satellite-measured Earth energy imbalance). Therefore, ECS is simply the product of the anthropogenic fraction of observed warming and the ratio of the doubled-CO2 forcing to the realized industrial-era forcing. By this method, midrange ECS proves to be 1.3 K, cohering nicely with the 1.4 K derived from the earlier observational method.

To verify this result, a billion-trial Monte Carlo simulation was conducted. It generated the expected somewhat right-skewed normal distribution, yielding midrange ECS on the interval 1.3 [1.0, 1.7] K. Note that the Monte Carlo distribution is for midrange ECS only. The upper bound may be as much as the 2.1 K suggested in Roy Spencer’s paper.

The value of simple analyses such as these lies precisely in their simplicity. Very nearly all media have now capitulated to the climate narrative, not least for fear of the Rufmord or reputational assassination to which all of us who have dared to raise “Please, sir” scientific questions about that narrative have been relentlessly subjected.

These simple, observational methods, particularly the first, are just about comprehensible even to the 97% of the population who tremble at the sight of even the simplest equation. The potential influence of these simple methods on the debate becomes still more compelling if they are combined with a simple benefit-cost analysis.

Risk vs. reward

For some years, the Global Warming Policy Foundation, which continues to produce solid research that is meticulously unreported in the media, has been trying to find out from the British Government’s notionally “independent” Climate Change Committee just how little global warming net zero emissions would bring about by 2050, and at just how much cost. The Committee has ducked and dived and wriggled, but has not produced definitive answers.

However, the British grid authority has calculated that just the capital cost of reconfiguring the grid for net zero would cost $4 trillion by 2050; but grid emissions account for only one-fifth of total UK emissions, and operating costs (opex) are generally at least twice the capital expenditure (capex). Just ask the Germans, who in a recent cold spell (blamed, of course, on global warming) have been paying $1.5 billion a week over the odds just to keep the lights on. In Britain, where coal-fired power used to cost $30 per MWh, the grid authority recently had to pay up to $11,500 per MWh at times of peak demand, and these multi-thousand-dollar rates are becoming more and more frequent as the contribution of thermal energy from coal and gas to the grid is destroyed by Government fiat, leaving the grid vulnerable to collapse.

Extrapolating the Grid’s figures to the whole energy sector, the capex cost of British net zero will be $20 trillion, five times the capex for reconfiguring the grid, while opex will be at least $40 trillion; total cost at least $60 trillion, which, at today’s prices, would represent three-quarters of the next 30 years’ total UK GDP.

Now let us assess how much global warming that massive expenditure on British net zero would prevent. In the past 30 years, the world’s emissions have driven a near-linear forcing of 1 Watt per square meter. If the whole world (let’s pretend) were to go to net zero emissions in a straight line, decrementing global emissions by 1/30th of the emissions in 2020 in each year to 2050, just over half a Watt per square meter of what would otherwise have been the next Watt per square meter of anthropogenic forcing would be abated.

Now, since one unit of straight-line forcing in the past three decades caused 0.4 K global warming, abating half the next unit of forcing over the next 3 decades would prevent just 0.2 K of the next 0.4 K warming, of which the British share would be 0.002 K. Yes, folks, one five-hundredth of a degree. At a cost of $60 trillion.

On that basis, each $1 billion that Britain and the world spends on chasing after net zero will prevent just one thirty-millionth of a degree of warming that would otherwise have occurred.

Value for money it isn’t. It is such simple but robust risk-reward calculations as these, as they become better known, that will deservedly kill the global warming narrative stone-dead.