By Michael Asten From: The Australian

THE Copenhagen climate change summit closed two weeks ago in confusion, disagreement and, for some, disillusionment. When the political process shows such a lack of unanimity, it is pertinent to ask whether the science behind the politics is as settled as some participants maintain.

Earlier this month (The Australian, December 9) I commented on recently published results showing huge swings in atmospheric carbon dioxide, both up and down, at a time of global cooling 33.6 million years ago.

Paul Pearson and co-authors in a letter (The Weekend Australian, December 11) took exception to my use of their data and claimed I misrepresented their research, a claim I reject since I quoted their data (the veracity of which they do not contest) but offered an alternative hypothesis, namely that the present global warming theory (which was not the subject of their study) is inconsistent with the CO2-temperature variations of a past age.

Some senior scientists, who are adherents of orthodox global warming theory, do not like authors publishing data that can be used to argue against orthodoxy, a point made by unrelated authors with startling clarity in the Climategate leaked emails from the University of East Anglia.

In the scientific method, however, re-examination of data and formulation of alternative hypotheses is the essence of scientific debate. In any case, the debate on the link between atmospheric CO2 and global temperature will continue since it is not dependent on a single result.

Another example is a study by Richard Zeebe and colleagues, published in Nature Geoscience, of a release of CO2 and an increase in temperature 55 million years ago. At this time there was an increase in global temperature of between 5C and 9C, from a temperature regime slightly warmer than today’s (that I will call moderate Earth) to greenhouse temperatures. It can be argued this example may have a message for humanity because the rate of release of CO2 into the atmosphere at the time of this warming was of a similar order to the rate of anthropogenic release today. However, the analogy turns out to be incomplete when the data is compared with present estimates of climate sensitivity to atmospheric CO2, and Zeebe and his colleagues conclude that the large temperature increase cannot be explained by our existing understanding of CO2 temperature linkage. Indeed, they write, “our results imply a fundamental gap in our understanding of the amplitude of global warming associated with large and abrupt climate perturbations. This gap needs to be filled to confidently predict future climate change.”

I argue there are at least two possible hypotheses to explain the data in this study: either the link between atmospheric CO2 content and global temperature increase is significantly greater (that is, more dangerous) than the existing models show or some mechanism other than atmospheric CO2 is a significant or the main factor influencing global temperature.

The first hypothesis is consistent with climate change orthodoxy. Recent writings on climate sensitivity by James Hansen are consistent with it, as was the Intergovernmental Panel on Climate Change in its pre-Copenhagen update, The Copenhagen Diagnosis.

Indeed, the 26 authors of the IPCC update went a step further, and encouraged the 46,000 Copenhagen participants with the warning: “A rapid carbon release, not unlike what humans are causing today, has also occurred at least once in climate history, as sediment data from 55 million years ago show. This `Palaeocene-Eocene thermal maximum’ brought a major global warming of 5C, a detrimental ocean acidification and a mass extinction event. It serves as a stark warning to us today.”

We have to treat such a warning cautiously because, as Pearson and his colleagues pointed out in their letter two weeks ago, “We caution against any attempt to derive a simple narrative linking CO2 and climate on these large time scales. This is because many other factors come into play, including other greenhouse gases, moving continents, shifting ocean currents, dramatic changes in ocean chemistry, vegetation, ice cover, sea level and variations in the Earth’s orbit around the sun.”

Sound science also requires us to consider the second of the above two hypotheses. Otherwise, if we attempt to reconcile Zeebe’s observation by inferring climate sensitivity to CO2 is greater than that used for current models, how do we explain Pearson’s observation of huge swings in atmospheric CO2, both up and down, which appear poorly correlated with temperatures cooling from greenhouse Earth to moderate Earth?

The two geological results discussed both show some discrepancies between observation and model predictions. Such discrepancies do not in any sense reduce the merit of the respective authors’ work; rather they illustrate a healthy and continuing process of scientific discovery.

In addition, unrelated satellite data analyses published in the past two years by physicist David Douglass and distinguished atmospheric scientist John Christy in two journals, International Journal of Climatology and Earth and Environment, provide observational evidence that climate sensitivity associated with CO2 is less than that used in present climate modelling, by a factor of about three.

Thus we have two geological examples and two satellite data studies pointing towards a lesser role of CO2 in global warming. This argument does not discount the reality of global warming during the past century or the potential consequences should it continue at the same rate, but it does suggest we need a broader framework in considering our response. The Copenhagen summit exposed intense political differences in proposals to manage global warming. Scientists are also not unanimous in claiming to understand the complex processes driving climate change and, more important, scientific studies do not unambiguously point to a single solution. Copenhagen will indeed prove to be a historic meeting if it ushers in more open-minded debate.

Michael Asten is a professorial fellow in the school of geosciences at Monash University, Melbourne.