A long thread of letters in The Canberra Times print edition, centring on curious claims by Tim Curtin.
First this letter appeared on Friday 31 July 2009:

The article “No time to lose as climate change turns to the worse” by Will Steffen, director of ANU’s Climate Change Institute (July 27, p9) contains some questionable statements as “fact”.

Steffen asserts “the climate system is now moving faster than we had thought likely a decade ago… the rate of accumulation of carbon dioxide in the atmosphere has increased since 2000 because of the growth in the global economy and the relative weakening of the natural processes that absorb carbon dioxide from the atmosphere”.

These statements are incorrect. The rate of growth of annual net increases in the atmospheric concentration of carbon dioxide was 7.44 per cent a year from 1960 to 1969, 10.01 per cent from 1970 to 1979, 7.16 per cent from 1980 to 1989, 4.55 per cent from 1990 to 1999, and just 2.8 per cent from 2000-2009 (the rates are for the years ending in June). Thus growth of net increases in atmospheric CO2 has been much slower than at any other time since records began at Mauna Loa in Hawaii in 1958.

It follows that while Steffen is right about rapid growth of the world economy from 2000 until 2008, he is wrong to say that “relative weakening of the natural processes…” explains his assertion that “climate change is turning for the worse”. The evidence is for strengthening those natural processes, namely the annual increase in photosynthesis that has accounted for more than half of all anthropogenic emissions of CO2 since 1959 – and explains the decline in the growth of those net emissions to Steffen’s “atmospheric accumulation”.

Tim Curtin, associate, RMAP, ANU

This was followed by assorted replies (including one from RMAP saying that Curtin was not in fact an associate of RMAP at all!).

Curtin then responded on 7 August with this:

Nick Ware (Letter, August 4) challenges my demonstration (Letters, July 31) that growth rates in atmospheric concentration of carbon dioxide have declined from 1960 to 2009.

He suggests I was using the “third derivative” – I wish I knew what that is! I simply derived the semi-logarithmic growth rates for each decade, those being the first derivative, like a normal compound interest growth rate over the period in question. The second derivatives (ie, the rate of change of the rate of change) also decline if you can be bothered to calculate them (unlike Will Steffen).

More seriously, Steffen in his article in The Canberra Times (“No time to lose as climate change turns to the worse”, July 27, p9) and in his piece (co-signed by 15 other worthies) in The Sydney Morning Herald (August 1) relies on James Hansen’s temperature data (NASA-GISS) which relies almost exclusively on temperatures measured at airports with ever-increasing planes, people and parked cars.

The truth is that at Mauna Loa where the atmospheric carbon dioxide level is measured, there is virtually no discernable trend in temperature since 1958, and none at all since 1978.

Finally, I must confess that when I signed my letter of 31 July I thought I was still an associate (unpaid) of RMAP at ANU. Sadly that is not the case, but even if I had been, I should not have used that designation.

Tim Curtin, Spence

My response:

Tim Curtin (Letters, 31 July and 7 August) makes a series of basic errors in his statements on climate change. The first is that it would make sense to measure the growth in carbon dioxide as if it were like compound interest. It doesn’t. Back to basics: CO2 increased by an average of 0.85 parts per million each year during 1960-69, by 1.27ppm for 1970-79, 1.60ppm for 1980-89, 1.50ppm for 1990-99, and by an average of 1.87ppm a year for this decade. There’s a clear long term trend here: the CO2 level is going up, and over time the amount it’s increasing by each year is growing. We’re already at around 390 parts per million: a higher level than humans have ever experienced, and already higher than the 350ppm that is increasingly regarded as the probable safe level for ecological and climatic stability.

Another error is the implication that the entire body of land surface temperature data – as used by NASA-GISS, Hadley, and many other climate science centres – is suspect, with the assertion that they rely “almost exclusively on temperatures measured at airports with ever-increasing planes, people and parked cars.” This is broadly known as the “urban heat island effect”, but it is well understood in meteorology and climate science, and temperature data is correlated and carefully adjusted to account for it. A series of studies published in Nature in 2004 compared temperature readings taken on calm nights with those taken on windy nights. The urban heat effect should be much stronger on calm nights, but the temperature trend was very strongly correlated. Overall the adjusted temperature data is sound, and is not undermined in any significant way by urban heat effects. The evidence for the warming trend is so strong that it’s essentially incontrovertible at present.

It’s amazing to me how armchair experts who clearly are not familiar with the science so often have the hubris to believe that they have some extraordinary insight that instantly overturns the entire scientific consensus. In reality, natural sciences don’t work that way. It’s all about the building up of many layers of evidence from a wide range of research teams, data sources, and physical systems, and arriving at conclusions based on the balance of probabilities. To date, there is no substantial evidence that constitutes a serious challenge to the mainstream science. The level of noise in the media from those who refuse to concede that humans are in the process of causing severe climate disruption is utterly out of proportion to their scientific strength of their arguments.

Matt Andrews, Aranda