Australia is faced, over the next generation at least and almost certainly much longer, with two environmental problems of great significance. They are, first, how to manage water in a dry continent and second, how to find acceptable alternatives to oil-based energy. Global warming is not one of those two issues.
I am presently agnostic about the central Anthropogenic Global Warming proposition. Three things about the AGW proposition make it, in my eyes, an inadequate basis for far-reaching public policy. One is what I would call over-certainty in the absence of convincing argument and data. Another is what seems to me an over-reliance on computer models.
The third is what I would call the almost panicky media mood about "global warming", in which human beings are pictured as evil actors in the destruction of their own habitation.
The story about anthropogenic global warming doesn't seem to stack up as the best science, despite the "thousands of scientists" who are said to have "consensus" about it. In climate science I see no consensus, only a pretence at a contrived one. In any case, whatever consensus exists in science is always temporary only.
Despite all the hype and the models and the catastrophic predictions, we human beings barely understand "climate". It is too vast a domain.
So to the first AGW proposition. Is our planet warming?
The IPCC has offered an estimated average increase in temperature for the planet over the 20th century of 0.6ºC ± 0.2ºC. On the face of it, there is nothing especially unprecedented about the 20th century temperature rise, given its "agreed" size. In the last million years long ice ages have been followed by much shorter "interglacial" periods, but these relatively brief warm periods have been the times when animal and vegetable life flourished. On balance a shift in temperature downwards of a few degrees will be much more worrying to us than a similar shift upwards.
Is the warming caused by our burning fossil fuels, clearing the forests and other human activities?
The truth is that no one has yet shown that it does. An increase in atmospheric levels of carbon dioxide over the past century is agreed. The physics of the greenhouse effect is straightforward, so that such a relationship is theoretically there. The crucial problem is that we don't know a lot about the positive and negative feedbacks involved with water vapour and clouds.
No dramatically linear relationship between increasing CO2 levels and higher global air temperatures can be shown for the 20th century. Though CO2 levels have been rising for a century, temperature has not done so: one of the warming periods in the 20th century seems to have been at the beginning of the century, when the human production of CO2 was much smaller than it is now. Temperatures seem not to have increased since 1998, though the concentration of CO2 in the atmosphere has gone on increasing.
Two other correlations are much stronger - the relationship between solar energy and temperature, and between ocean movements and temperature. Moreover, actual measurement of temperature does not support the greenhouse gas theory. According to the IPCC's global climate models there ought to be a "hot-spot" in the troposphere at about 10km up. However, the data presently show no sign of it.
On the evidence that is available, I think it has to be said that the assertion that the increase in carbon dioxide has caused the temperature to rise is no more than an assertion. There is simply no evidence that this causal relationship actually exists.
This is an edited extract of a speech delivered to the Planning Institute of Australia, Canberra, April 2, 2008. The entire speech can be downloaded by clicking here (PDF 258KB).
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