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Using IPCC numbers we can expect only half a degree of warming this century. Time to Panic?

Christopher Monckton calculates below that even if we assume the IPCC and mainstream estimates are right, the warming from here to 2100 is likely to be a minor half a degree. (He doesn’t even bother to argue about whether this would be beneficial or not). Monckton just makes the point that for all the scare campaign about preventing a “two degree” apocalypse, what we are really talking about is a half degree in the next ninety years with some theoretical further warming in the centuries after that. The “two degrees” of fear is measured from the bottom of the Little Ice Age, as if that was the ideal “pre industrial” climate that we somehow want to return to.

As usual, everything about the Great Global Warming Scare falls apart under the most cursory glance, yet the billion dollar PR truck rolls on. The climate sensitivity of the IPCC dropped in Assessment Report 5 to about 2.2 C as it slowly is dragged toward a more realistic number.  The data coming in tells us that the climate feedback factors are likely net negative, so climate sensitivity is below 1°C. Hence even a  “half a degree” due to CO2 is an overestimate.

— Jo


Guest Post by Christopher Monckton of Brenchley

2 C° or not 2 C°?

In 2009 the Copenhagen climate summit asserted, on little evidence, that global warming of 2 C° compared with pre-industrial temperature [equivalent to 1.1 C° above today] would be dangerous. The UK Climate Change Committee said in 2015: “If we make no efforts to cut global use of fossil fuels, global warming is likely to reach between 2-7°C this century with further warming beyond.” A Science editorial in July 2015 said: “Let’s act now, to save the next generations from the consequences of the beyond-two-degree inferno.”

Equilibrium climate sensitivity ΔT to a CO2 doubling is given by

ΔT = λ0 ΔF (1 – λ0 f ) –1

where the Planck sensitivity parameter λ0 = 0.3125 K W–1 m2 (IPCC AR4, p. 631 fn.); the CO2 forcing ΔF is generally taken as 5.35 ln 2 W m–2 (Myhre et al, 1998; IPCC TAR); and uncertainty in constraining ΔT arises chiefly from the feedback sum f, for which IPCC’s estimates (best estimates are in bold face) were cut from 1.95 [1.55, 2.35] W m–2 K–1 in AR4 to 1.55 [1.00, 2.25] Wm–2 K–1 in AR5 (Fig. 9.43(a), detail): The mainstream climate sensitivity estimates to a CO2 doubling, at 1-8 below, reveal a monotonic decline from SAR to AR5, which readopts the interval in FAR (cf. Charney (1979, p. 4), though AR5 states no central estimate, which should, however, have been given as 2.2 K where f = 1.55 Wm–2 K–1 (8 below).


Table1: Estimates of sensitivity
Est. Source / basis Sensitivity
1  1995 IPCC SAR (17 models: AR4, p. 798, box 10.2)  3.8 [3.0, 4.6] K
2  2001 IPCC TAR (15 models: AR4, p. 798, box 10.2)  3.5 [2.6, 4.4] K
3  2007 IPCC AR4 (18 models: AR4, p. 798, box 10.2)  3.3 [2.6, 4.0] K
4           IPCC AR4 stated interval  3.0 [2.0, 4.5] K
5           IPCC AR4 implicit interval from (1), where f falls on 1.95[1.55, 2.35]  3.0 [2.2, 4.4] K
6           IPCC FAR stated interval (cf. Charney, 1979, p. 4)  3.0 [1.5, 4.5] K
7  2013 IPCC AR5 stated interval         [1.5, 4.5] K
8            IPCC AR5 implicit interval from (1), where f falls on 1.55[1.00, 2.25]  2.2 [1.7, 3.9] K
   Warming to 2100
9  Only half of equilibrium warming will arise in the century after a forcing  1.1 [0.9, 2.0] K
10  Forcings rise linearly so that ~50% of warming will occur by 2100  0.6 [0.4, 1.0] K

IPCC 21st-century warming estimates indicate that it assumes, in line with Roe (2009), that only half of equilibrium warming will occur in the first 100 years after a forcing (9 above). Furthermore, forcing does not arrive as a single pulse but increases over the century, halving the in-century warming (10) and putting the remainder in the following century, by which time fossil fuels will approach exhaustion. Remaining warming to equilibrium at 2.2 K above today would be spread over the subsequent 1000-3000 years (Solomon et al., 2009), allowing plenty of time for adaptation.


No warming has yet arisen this century. Warming may be 0.6 K by 2100, could be as low as 0.4° K and will not exceed 1° K. Allowing for negative aerosol forcings in SAR to AR5, or for net-negative temperature feedbacks (Lindzen & Choi, 2011; Spencer & Braswell, 2011; Monckton of Brenchley, 2015), warming may well not reach these values, but is most unlikely to exceed them.


IPCC, Assessment Report 4, 2007, Working Group 1, The Physical Science Basis, Chapter 8. [PDF]

Lindzen, R. & Yong-Sang Choi, Y, (2011) On the Observational Determination of Climate Sensitivity and Its Implications, Asia-Pacific J. Atmos. Sci., 47(4), 377-390, 2011 [PDF]

Mhyre et al (1998)  New estimates of radiative forcing due to well mixed greenhouse gases, GRL, DOI: 10.1029/98GL01908

Spencer, R. W.; Braswell, W.D. (2011) On the Misdiagnosis of Climate Feedbacks from Variations in Earth’s Radiant Energy Balance, Remote Sens. 2011, 3, 1603-1613. [PDF]

Solomon et al (2009) Irreversible climate change due to carbon dioxide emissions. PNAS, doi: 10.1073/pnas.0812721106




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