IPCC silently slashes its global warming predictions in the AR5 final draft

Guest essay by Christopher Monckton of Brenchley

Unnoticed, the IPCC has slashed its global-warming predictions, implicitly rejecting the models on which it once so heavily and imprudently relied. In the second draft of the Fifth Assessment Report it had broadly agreed with the models that the world will warm by 0.4 to 1.0 Cº from 2016-2035 against 1986-2005. But in the final draft it quietly cut the 30-year projection to 0.3-0.7 Cº, saying the warming is more likely to be at the lower end of the range [equivalent to about 0.4 Cº over 30 years]. If that rate continued till 2100, global warming this century could be as little as 1.3 Cº.

Official projections of global warming have plummeted since Dr. James Hansen of the Goddard Institute for Space Studies told the U.S. Congress in June 1988 the world would warm by 1 Cº every 20 years till 2050 (Fig. 1), implying 6 Cº to 2100.

Figure 1. Projected global warming from 1988-2019 on three scenarios (above), and from 1988-2060 on scenario A only (below), based on Hansen (1988), who testified before the U.S. Congress that June that scenario A was his business-as-usual case. The trend from 1988-2050 on that scenario (arrowed) is approximately 0.5 Cº/decade.

IPCC (1990: p. xi) projected warming of 0.2-0.5 Cº/decade to 2100. IPCC (1995: p. 6) projected 0.1-0.35 Cº/decade. IPCC (2001: p. 8) projected 0.13-0.43 Cº/decade to 2050. IPCC (2007: p. 13, table SPM.3) projected 0.11-0.64 Cº/decade to 2100.

Figure 2. Near-term warming projections (2005-2050) relative to 1986-2005, based on 42 models (colors) against observations (black). The second-order draft of IPCC (2013) projected global warming at 0.4-1.0 Cº over 30 years (red arrows), equivalent to 0.13-0.33 Cº/decade. The final draft projected warming at 0.4-0.7 Cº over 30 years (green arrows), equivalent to just 0.10-0.23 Cº/decade. Diagram based on IPCC (2013, Fig. 11.25a).

The second-order draft of IPCC (2013: fig. 11.33) had projected 0.13-0.33 Cº/decade to 2050. However, the final draft slashed this projection to 0.10-0.23 Cº/decade (Fig. 2), the IPCC’s best guess being closer to the lower than to the upper bound of the revised range.

The projected range in the second-order draft had been consistent with the models, but the revised range in the final draft was at the low end of models’ projections (Fig. 3). Implicitly, the IPCC no longer accepts that models accurately project warming.

The IPCC says:

“Overall, in the absence of major volcanic eruptions – which would cause significant but temporary cooling – and, assuming no significant future long term changes in solar irradiance, it is likely (>66% probability) that the GMST [global mean surface temperature] anomaly for the period 2016–2035, relative to the reference period of 1986–2005, will be in the range 0.3°C–0.7°C (expert assessment, to one significant figure; medium confidence).” (IPCC, 2013, p. 11-52).

Figure 3. Above: Models’ global warming projections, 2016-2035 vs. 1986-2005, against the IPCC’s projected interval of 0.4-1.0 K over 30 years, equivalent to 0.13-0.33 K decade^–1 (between the gray dotted lines, based on IPCC 2013, 2^nd draft, fig. 11.33c). Below: Final draft’s revised interval of 0.3-0.7 K over 30 years or 0.10-2.33 K decade^–1, visibly at the low end of models’ projections (based on IPCC, 2013, fig. 11.25c). This implicit rejection of the models’ forecasting skill has passed unnoticed until now. Reviewers of the second draft were not consulted about the change in the IPCC’s key near-term projections, though many had argued for it.

The IPCC’s explicit reliance on its own “expert assessment” rather than upon the models’ projections is a significant climbdown. However, even its reduced best estimate of 0.13 Cº/decade may still be on the high side. Observed outturn since 1950 has been below 0.11 Cº/decade (HadCRUT4, 2013: Fig. 4).

Figure 4. Global mean surface temperature anomalies and 0.11 Cº/decade least-squares trend, January 1950 to November 2013 (from HadCRUT4 data).

That is not all. Despite record increases in CO2 concentration, there has been no global warming for almost 13 years (mean of GISS, HadCRUT4, NCDC, RSS, & UAH temperature data: Fig. 5), or, by satellite measurements, for more than 17 years (RSS, 2013: Fig. 6), and no warming distinguishable from the combined measurement, coverage, and bias uncertainties for 18 years (HadCRUT4, 2013: Fig. 7).

Figure 5. Monthly global mean surface or lower-troposphere anomalies (dark blue) and least-squares linear-regression trend (bright blue: mean of GISS, HadCRUT4, NCDC, RSS, and UAH data), January 2001 to November 2013, showing no global warming for almost 13 years notwithstanding continuing rapid increases in atmospheric CO2 concentration (gray).

Figure 6. Despite a near-linear increase of 2 μatm/year in CO2 concentration (NOAA, 2013, gray), the least-squares linear-regression trend (bright blue) on the RSS satellite monthly global mean lower-troposphere anomalies (dark blue) has been zero for 17 years 3 months (207 months).

Figure 7. HadCRUT4 monthly global mean surface temperature anomalies and trend, February 1996 to November 2013, showing a linear trend entirely within and hence indistinguishable from the combined measurement, coverage, and bias uncertainties.

In the light of the growing divergence between projection and observation, a direct comparison between the IPCC’s now-reduced near-term global warming projections and observed temperature change since 2005 is of value as a performance indicator for the models’ global-warming projections.

Fig. 8 shows such a comparison, based on the downgraded projections in IPCC (2013, fig. 11.25a: see Fig. 2 above). In the nine years since 2005, a divergence of 0.15 Cº has occurred.

Figure 8. Orange region: Models’ projections of global warming, January 2005 to November 2013, on the interval 1.33 [1.0, 2.33] Cº/century (from IPCC, 2013, fig. 11.25a). The second draft’s mid-range estimate is the final draft’s high-end estimate; the former low-end estimate is now the central estimate. Thick red trend-line: central projection of 0.12 K warming over the 107-month period, equivalent to 1.33 Cº/century. Gray curve and trend-line: monthly CO2 concentration anomalies (NOAA, 2013) and 18 μatm (198 μatm/century) trend, which caused 0.24 W m^–2 forcing (or 0.35 W m^–2 including other anthropogenic forcings). Of the 0.21 Cº warming projected to arise from this forcing, almost half was previously committed. Thick bright blue trend-line: Global cooling of 0.03 Cº (0.30 Cº/century: mean of five datasets). Over the period, the models over-predicted global warming by 0.15 Cº (1.6 Cº/century).

Multiple lines of evidence now confirm that the models and consequently the IPCC have overestimated global warming. Yet neither that misconceived organization nor any of its host of unthinking devotees has displayed any remorse. Instead, they persist in maintaining that the warming is temporarily paused, though they cannot really explain why; or they blame particulate aerosols, their get-out-of-jail-free fudge-factor; or they pretend warming is really continuing unabated, saying it has gone into hiding deep in the oceans where, conveniently, we cannot measure it, or that the Earth-atmosphere system has a fever driven by four atom-bombs’-worth of heat content increase every second.

What they are not prepared to countenance, notwithstanding the real-world, measured evidence, is the growing probability that they and their precious models have so badly misunderstood the climate, or so well understood it and so badly misrepresented it, that global warming is simply not going to occur at anything like any of the exaggerated rates that they had until now so confidently over-predicted.

Do not underestimate the importance of the IPCC’s climbdown, albeit that it is furtive and that there is not a hint of it in the Summary for Policymakers – the only part of the latest assessment that lazy politicians and incurious journalists may ever get around to reading.

Figure 9. Five projections of global warming, 1990-2050, compared with the linear trends on two observed datasets. IPCC projections are mid-range estimates. The trend (green) on the HadCRUt4 monthly global mean surface temperature anomalies reflects the warming at 0.11 K decade^–1 observed since 1950. The trend (dark green) on the RSS satellite data reflects the zero trend that has now persisted for more than 17 years. Both observed trends are extrapolated to 2050.

If anyone ever again tries to tell you The Science Is Settled, as the now-axed Klimate Kommissariat in Australia is still trying to do in its latest taxpayer-funded propaganda sheet, point to Fig. 9 and ask two questions.

First, point to the red zone marked Projections and ask which of the very wide range of official projections The Science has Settled upon.

Secondly, point to the green zone marked Observations and ask why the real climate has so persistently failed to pay any attention to the Settled Science.

Then sit back and listen to the increasingly demoralized and disjointed flannel. As the nonsense runs down, the game is up.

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References

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/pub/data/anomalies/monthly.land_ocean.90S.90N.df_1901-2000mean.dat.

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