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The Garnaut Reviews’ errors and material omissions

By Tim Curtin - posted Friday, 25 March 2011


Note: The world’s uptakes of atmospheric carbon dioxide are not limited to cereals - other food and fruit crops, livestock, forestry, and fisheries are all contributors.

Statistics and the Garnaut Reviews

Garnaut’s The Science of Climate Change is notable as much for what it leaves out as for what it thereby tendentiously includes. The list begins with Garnaut’s first “key point”:

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Observations and research outcomes since 2008 have confirmed and strengthened the position that the mainstream science then held with a high level of certainty, that the Earth is warming and that human emissions of greenhouse gases are the primary cause. ..The statistically significant [sic] warming trend has been confirmed by observations over recent years:  global temperatures continue to rise around the midpoints of the range of the projections of the Intergovernmental Panel on Climate Change (IPCC) and the presence of a warming trend has been confirmed [sic].

Garnaut adds “I asked two leading econometricians (Trevor Breusch and Farshid Vahid), to examine the temperature record from the three authoritative global sources”. Actually, there are five, and the three assigned to Breusch and Vahid are not independent of each other, while Garnaut failed even to mention the more comprehensive global coverage of satellite data sets (UAH and RSS). Breusch and Vahid also failed in their primary duty of due diligence by not checking them anyway, which enabled them to find “there is sufficient statistical evidence in the temperature data of the past 130-160 years to conclude that global average temperatures have been on a warming trend”. But this factoid depends heavily on the absence of the hot tropics from global temperature sets for the period between 1850 and 1910 (see Fig.1), as it was not until the 1950s that global temperature becomes a valid statistic, for only then did global surface temperature coverage reach 80 per cent, and it is now below that level again, with the disappearance in the Breusch-Vahid data of many surface stations from cold northern Canada and Siberia since 1990. Even in the USA there has been a decline in station numbers (USHCN) from 1421 in 2002 and 1164 in 2007, apparently mostly in cooler northern and high altitude regions. One expects professional statisticians and economists to check the provenance of the data they use, and there is no evidence for that in Breusch-Vahid-Garnaut.

The truth is shown in Fig.2: the linear trend in the UAH satellites’ global data from December 1978 to February 2011 has an R2 of 0.345, and indicates a rise of 0.0012 oC per month since 1978, or 0.0144 p.a., 0.144 per decade, and 1.44oC per century, well below the 3oC predicted by the IPCC, let alone the 5oC predicted for 2100 by Garnaut (2008:Fig.4.5) if there is no “mitigation” of Business as Usual emissions, BAU).  The UAH data do not in fact “corroborate” the NASA-Gistemp temperature data for the period when they overlap, with the annual change in the Gistemp series (1979-2010) at 0.0196oC, which is 36 per cent higher than the UAH trend of 0.0144 oC.

Garnaut’s 8 Update Reports and 2008 Review are both in the nature of a Prospectus, inviting the Government and people of Australia to invest in a Carbon Tax that will save them the costs of “dangerous climate change”. That means Garnaut’s 2008 and 2011 reviews should have disclosed the UAH and RSS satellite data as well as the Gistemp/NCDS/HadleyCRU surface data, even if using the former would have diluted the all too evident advocacy that characterises the Garnaut reviews.

However, there is a much more serious omission of “all the information investors and their advisors would require and expect” in both the Garnaut Reviews when they make this statement:

No-mitigation case – based on no action undertaken to mitigate climate change, and used as a ‘reference’ to assess the benefits of climate change action that accrue from the climate change impacts that are avoided. By the end of the century the concentration of long-lived greenhouse gases in the atmosphere is 1565 ppm carbon dioxide equivalent (Garnaut 2011:5 and Fig.1, my emphasis).

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The present atmospheric concentration of CO2 is 390 parts per million (ppm) of the atmosphere. To this Garnaut adds the atmospheric levels of other greenhouse gases, chiefly methane (CH4) and nitrous oxide (N2O), which are expressed in CO2 “equivalent” amounts that bring the CO2e concentration to between 455 and 465 ppm in 2010. To get from 460 ppm to 1565 ppm by 2100 requires that the rate of growth of CO2e from now until 2100 has to be 1.0137 per cent p.a. The actual growth of atmospheric CO2 from 1958 to 2010 was 0.295 per cent p.a., and projecting CO2e at that rate (the growth rates of CH4 and N2O are much lower than that of CO2, see IPCC, Solomon et al. 2007:141) to 2100 produces only 600 ppm of CO2e by 2100, less than 38 per cent of (i.e. 62 per cent less than) Garnaut’s 1565 ppm.

At the observed atmospheric concentration growth rate of 0.295 per cent p.a. over the longer period from 1959 to 2009, it will take until 2134 for the pre-industrial level of the atmospheric concentration of 280 ppm to double to 560 ppm; and the 2009 level of 387 ppm will not double until 2244.   Garnaut offers no basis for predicting any acceleration in the rate of growth of the atmospheric concentration of CO2e above the actual rate from 1958 to 2010, and, failing that, this is like Lihir claiming in its 1995 Prospectus that it could borrow at one percent above LIBOR instead of the 2-3 percent it did have to pay to its main bank lender, UBS. Had Lihir

made that claim, the ASX might well have rejected the Prospectus – and if not, shareholders would have been able to sue Lihir when the truth became apparent.

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About the Author

Tim Curtin has worked as a journalist, economist and advisor. He lives in Canberra.

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