In the following open letter
to the President of the Australian Academy of Science, William Kininmonth explains that the science of climate change is ‘not settled’ and if the scientific community is to get to a position where it can confidently prediction future climate it will be necessary to both understand why and how the climate system has varied in the past, and to have a robust computer construct of the climate system. Given so far we have neither, the recent very public criticisms of Ian Plimer’s new book ‘Heaven and Earth’ are not logical or consistent.
Dear Professor Lambeck,
I was Interested in your views of Ian Plimer’s book, Heaven and Earth, given in the transcript of your interview on the ABC’s Okham’s Razor. As President of the Australian Academy of Science your opinions carry considerable influence. Based on your own understanding of science and the wide expertise within the Academy that you could draw from I expected a reasoned evaluation, both of the science of climate change and the sociological processes that may have led to the divergent views that exist on the magnitude of human influence. I was disappointed and suspect that many others will have been similarly disappointed.
You certainly set the scene correctly when you stated:
“There is no dispute that the geological record shows that climate change has occurred throughout the earth’s history. The dispute is over whether the modern record can be understood in terms of the natural background processes or whether there is a new human factor that changes the rules about climate change.
To address this requires more than geological insight. It requires an understanding of the underlying physical, chemical and biological processes and an ability to model them so as to test alternative hypotheses.”
However, you fail to follow up and address the arguments advanced by Plimer that the recent record is not unusual, and that the human factor is not significant. Indeed, having correctly set out the basis for evaluation you largely ignore your own terms of reference!
The reality is that, except in the most general terms, we are unable to satisfactorily explain past variations of climate. Over the recent 2 million years why did the primary mode of climate oscillation change from a 40,000 year (axial tilt) periodicity to one close to 100,000 years (linked to eccentricity)? And how do we explain the recent glacial cycles, given that annual solar insolation intercepted by the Earth’s disc changes little between near circular and more eccentric orbits? Even the relative regularity in value to which temperatures asymptote during each interglacial, as estimated from Antarctic ice cores, can hardly be attributed to chance yet does not have an explanation!
And if we are unable to satisfactorily explain the past, how can we explain the future?
Of significance then is the arguments for the human factor in climate change. Will the human influence be sufficient to cause a shift to a new climate state that is dangerously different to the current one with its known variations? Plimer makes two points on this: firstly he notes the well established logarithmic relationship between radiative forcing and the increase in CO2 concentration; and secondly he notes how evaporation of latent energy constrains surface temperature rise.
The logarithmic relationship between radiative forcing and the increase in CO2 concentration is referred to in each of the IPCC assessment reports. It is not controversial and identifies the constant incremental increase in radiative forcing for each doubling of CO2 concentration. In a graphical form this is demonstrated in Plimer’s Figure 50, page 375 (What is controversial in Figure 50 is the implied relationship between radiative forcing and temperature, but the principle is captured). The approximately 3.7 W/m2 radiative forcing is the same for any doubling of CO2 concentration. Equally importantly, most (approximately 60 percent) of the greenhouse effect of CO2 is in the first 50 ppm concentration. Because of the logarithmic relationship the increase in CO2 concentration increase alone does not give rise to the suggestion of passing a ‘tipping point’ to dangerous global warming.
The constraining effect of evaporation of water vapour on surface temperature rise is well documented in a 1966 paper by Bill Priestley, former Chief of the CSIRO Division of Meteorological Physics, where the physical basis of why temperatures are much lower over well-watered surfaces than dry surfaces was explained.
Plimer takes this up on page 373 where he identifies that an increase in surface temperature of 1oC will generate an increase in surface energy loss of 10 W/m2 (the text has an obvious misprint, where 1 W/m2 is erroneously quoted) and a 3oC temperature rise will generate an increase in surface energy loss of 30 W/m2. Clearly, the direct radiative forcing of about 3.7 W/m2 from a doubling of CO2 concentration can only sustain a surface temperature rise of under 0.4oC, a significantly different projection than that given by the computer models used in the IPCC fourth assessment that are up to an order of magnitude larger.
A question arises as to why the computer models project a global mean temperature rise that is an order of magnitude larger than basic physics would suggest. One reason might be that there is apparently a fundamental deficiency in the representation of the hydrological cycle in the computer models. This has been independently identified by two groups assessing the computer models and is published in the peer reviewed literature (Journalof Climate, Science). In the computer models the rate of increase of evaporation and latent energy exchange is only about one-third that expected by the Claussius Clapeyron relationship, thus reducing the constraining influence over surface temperature rise of evaporation. The attached paper elaborates on the essential physics in more detail.
The immediate interest is in how the computer models will respond once the identified deficiency in surface evaporation response is corrected. Will they continue to portray apparent runaway global warming or will a better-represented hydrological cycle constrain temperature response? Although local computer modellers have been alerted to the evaporation deficiency its significance does not seem to be recognised. Overseas modelling groups are now working on the problem and with time a resolution of the theoretical versus modelling differences will be available. Our understanding of surface energy exchange processes suggests that 30-31oC is a natural asymptote ocean surface temperature for an interglacial that is relatively insensitive to CO2 forcing.
The point of this email is to alert you (and through you the wider academy) that the science of climate change is not as settled as you have led the public to believe. As you have correctly noted, “No single discipline is equipped to handle the complex problems of climate change”. However, if the scientific community is to get to a position that confident predictions of future climate can be made then it is necessary to both understand why and how the climate system has varied in the past, and to have a robust computer construct of the climate system for predictions. As yet we have neither. As a consequence, the criticisms that you have made of Ian Plimer’s book do not meet the benchmarks of assessment that you set at the commencement of your interview.