Two reasons for caution in climate mitigation

Ross Garnaut says that he now believes climate change to be ‘a worse and more urgent problem’ than he believed beforehe began his enquiry. Although his Interim Report (Section 2.1) accepts the IPCC projections only ‘on the balance of probabilities’, it seems clear that Professor Garnaut is personally convinced that the outlook for Australia is at least as bad as the IPCC’s extreme A1F1 Scenario; that is, a warming of more than 0.2c/decade for the first few decades of this century. He is especially concerned by the high levels of carbon emissions that have been produced by spectacular growth rates in emerging economies such as China. Accordingly, his Review’s Interim Report concludes that the evidence “suggests that it would be in Australia’s interests to seek international agreement on the most ambitious feasible global mitigation target” (Section 3.2 of the Interim Report).

I am disappointed that the Garnaut Review has so far accepted, without substantial critical analysis of its own, the most extreme scenarios developed by the IPCC’s modelers. A model is an abstraction that necessarily leaves out many features of the world (that’s its value as a model) . But simplification qualifies the predictive power of a model’s projections. I am surprised that economists such as Garnaut (or Stern or Nordhaus, for that matter) who are familiar with the frailty of complex models of the economy seem inclined to accept the projections of climate models without carefully checking them against current observations. There are strong reasons, I believe, for questioning both the reliability of the IPCC’s model-based projections of temperature trends and the carbon-forcing theory that supplies the IPCC’s mechanism of man-made climate change.

Reasons for questioning the temperature projections

The Garnaut Review’s Interim Report confines its tests of the credibility of the A1F1 scenario, for example, to a couple of paragraphs and a couple of low-resolution graphics that it takes from a 1-page report by Rahmstorf et. al. published in the journal Science in May 2007 that now appears to have been mistaken. Rahmstorf and others claim that the observed temperature trends over the period 1990-2006 were “the upper end” of the range of IPCC temperature projections for the 1990-2006 period—a conclusion that the Garnaut Interim Review adopts at Section 2.4. But the data on emissions and temperatures in the IPCC reports for the period 1990-2000 were fixed parameters built into the SRES scenarios and not projections. In the IPCC Assessment Reports, only the trends projected beyond 2000 derive from the IPCC models, which means that Rahmstorf’s assessments are based on 5 years of actual projections (2000-2006), not 16 years (1990-2006) and therefore subject, at a minimum, to much greater degrees of uncertainty (see the discussion of Rahmstorf et al. here).

The IPCC’s SRES scenarios have not changed since their publication in 2000. They were not updated (deliberately) for the 2007 Fourth Assessment Report in order to preserve their capacity to show variations in outcomes due to differences in the scenario parameters. Accordingly, data used to determine parameters for the scenarios such the A1F1 Scenario refer to the period before 2000. The projections of the models reflecting each scenario begin from 2000. The former Australian Statistician, Ian Castles, has confirmed this fixation of the data from records of the preparations for the 2007 IPCC report.

The science of climate change must provide test-able, that is falsifyable, propositions to be science. Those propositions are found in the projections of the IPCC models of temperature trends after 2000. Now Lucia Liljegren has succeeded in showing that those projections are wrong for the period 2001-2008, denting the credibility of the IPCC models and, a fortiori, the Rahmstorf conclusion (adopted by the Garnaut Interim Report) that observed temperatures are “at the upper end” of the A1F1 projected range.

Using statistical methods that ensure robust regression analysis of the temperature data time-series, Liljegren has shown that trends in the observed temperature data from 2001 to 2008 diverge significantly from the IPCC projected trends, revealing a decline in temperatures at a rate of -1.1c/Century (as opposed to the IPCC’s ‘mid-range’ projections of more than 2.0c/Century). Her careful analysis does not, as Liljegren observes, show that the global warming has gone away (she is convinced that anthropogenic warming is happening). Rather, they show that the IPCC projections don’t come even close to projecting the temperature trends for the last seven years: that is for the period since 2001 when IPCC projections began. If there is another upturn in temperature trends following this recent period of shallow decline, then concerns about warming trends will look more credible again. But the IPCC projections won’t be repaired by an upturn in temperature. Whatever happens next, the IPCC’s projections—and hence, their models—seem to need revision.

Liljegren is not the only statistician recently to fault the IPCC/SRES projections. David Stockwell, an ecosystem modeler, has shown that a simple linear regression of the temperature data over the past decade provides sufficient reason to consider the IPCC projections ‘highly unlikely’

“[T]he trend in temperatures for the last 10 years is so low, that an increase of 0.2C per decade could be rejected in 3 out of 4 indices [That is, temperature series. PWG]with some level of confidence. In one case, using the IPCC terminology, these results suggest IPCC projection of global warming this century are very unlikely (1-10% chance) to be correct. This is a controversial result contradicting the IPCC ‘consensus’ position.” Niche Modeling

Reasons to question the carbon-forcing thesis

click for larger image

Although the Garnaut Review makes no attempt seriously to consider question the evidence for this theory, there is very little evidence (or none) of any correlation between the monotonous growth in the CO2 concentrations in the atmosphere and the variations in global temperature anomalies. It doesn’t take much skill to discover this as shown by the graphic (click the thumbnail to see it full-size) that I created from publicly available data. CO2 concentrations as measured by the Scripps Oceanographic Institute at Mauna Loa, Observatory, Hawaii, have increase steadily with pronounced but regular seasonal variations since they were first measured in the 1960s. It is evident that the CO2 trends look nothing like the lower-troposphere (i.e. surface) temperature anomaly trends (from RSS satellite data). Five minutes with Excel (or a statistical package such as R) shows that the correlation (r2) between the two series is non-existent (see also this article by J D’Aleo).

This is only amateur observation. Not proof of anything but ample reason to question the evidence for a theory that leads Professor Garnaut to recommend a dramatic re-pricing of carbon-based energy production in Australia. There is, also, more damning recent data that seems to falsify the predictions of the CO2 thesis

One of the key predictions of the CO2-water-vapor feeback-loop that drives the greenhouse effect dominating IPCC thinking is that temperatures in the troposphere (between 450 hPA and 750 hPA of atmospheric pressure) In the tropics should rise faster than surface temperatures as vertical convection currents drive heat distribution. This effect has been called the ‘characteristic emission layer’ demonstrating the water-vapor feedback cycle that the CO2 emissions initiate.

Now a paper in the International Journal of Climatology by Douglass et al. appears to demonstrate that this “characteristic” effect does not exist.

“Models are very consistent, as this article demonstrates, in showing a significant difference between surface and tropospheric trends, with tropospheric temperature trends warming faster than the surface. What is new in this article is the determination of a very robust estimate of the magnitude of the model trends at each atmospheric layer. These are compared with several equally robust updated estimates of trends from observations which disagree with trends from the models. The last 25 years constitute a period of more complete and accurate observations and more realistic modelling efforts. Yet the models are seen to disagree with the observations. We suggest, therefore, that projections of future climate based on these models be viewed with much caution. “

Update :The data sets used in the Dougalass et. al. paper have been challenged by the contributors to Real Climate (26 March, 08)

One Comment

  • Chris H. wrote:

    One of the great things about the Garnaut report (and the Stern report in the UK) is that they are done by non-scientists. In other words, if they had any biases perceived it might be in denial. At least they understand how science works and that there really is an urgent need for action. One suggestion I’ve seen that crosses the boundaries of science, big business and economics is the adaptation of medical triage ideas to climate – see for more information. There’s lots of good ideas there that deserve a debate

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