This note by The Viscount Monckton of Brenchley uses methods and data exclusively from mainstream climate science to constrain the interval of 21st-century global warming.
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 (1),
ΔT = λ0 ΔF (1 – λ0 f ) –1, (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] W m–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 W m–2 K–1 (8 below).
|Est.||Source / basis||Sensitivity|
|1||IPCC SAR (17 models: AR4, p. 798, box 10.2)||3.8 [3.0, 4.6] K|
|2||IPCC TAR (15 models: AR4, p. 798, box 10.2)||3.5 [2.6, 4.4] K|
|3||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||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.
Conclusion: 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.