Sound science is based upon observation, experiment and the testing of hypotheses in the context of the principle of simplicity (often termed Occam's Razor). The unvalidated computer models that now dominate the public face of climate ''science'' are a jungle of complexities, and represent speculative thought experiments not empirically tested science. In support of these methods, the former director of the British Meteorological Office, Professor John Mitchell, has said that ''people underestimate the power of models. Observational evidence is not very useful … Our approach is not entirely empirical''. The last part of this statement is only too true, and leads to the discomfit expressed by those such as the British engineering professor John Brignell: ''The ease with which a glib algorithm can be implemented with a few lines of computer code, and the difficulty of understanding its implications, can pave the path to cloud-cuckoo land.'' Climate science is not primarily about modelling, albeit a powerful tool, but about testing hypotheses against key empirical facts, including:

Atmospheric carbon dioxide is a mild greenhouse gas that exerts a diminishing warming effect as its concentration increases; We live in a carbon dioxide-starved world (levels 15 times higher having been reached about 500 million years ago and diminishing since); Carbon dioxide is a vital plant fertiliser; The world warmed in the earlier and latter parts of the 20th century; and The world has cooled slightly over the past 10 years despite a 5 per cent increase in carbon dioxide.

These facts are consistent with the conclusion that enhanced levels of carbon dioxide are good for the environment , and do not cause dangerous global warming. Professor Chubb claims: ''Ross Garnaut has summarised the state of climate science in his recent report.'' But what Professor Garnaut in fact summarised were the official findings of the UN's Intergovernmental Panel on Climate Change (IPCC), an undeniably political body. Professor Garnaut also said that IPCC views are supported ''by the learned academies of science [all disciplines] in all of the countries of scientific accomplishment''. Which invites the obvious response, ''Well, they would say that, wouldn't they?'' The ''IPCC and most academies'' line is, of course, the argument from consensus, which raises the question: When did you last hear a scientist say ''there is a consensus that the sun will rise tomorrow''? Never, of course, for the very use of the phrase ''consensus'' in science tells you that a matter is not settled. Global warming science is not just unsettled but profoundly uncertain and controversial. Consensus is a political, not scientific, concept. As Michael Crichton wrote: ''There is no such thing as consensus science. If it's consensus, it isn't science. If it's science, it isn't consensus. Period.''

Returning to real science, Professor Chubb said that when ''science is conducted properly, and interpreted after extensive, and critical, analysis, knowledge and understanding is increased and improved. We shift [our views] or confirm what we think.'' Quite so, and nothing about consensus there. But the problem remains of improper science, which is now widespread. In particular, the IPCC - which was set up to advise only on the climatic effect of human greenhouse emissions - has shown repeatedly that it is not in the business of shifting its beliefs, whatever the evidence; instead, facts contrary to its convictions are either ignored or neutralised by adjusting the models. For example, the sun recently entered a quietude unknown since the Little Ice Age. Accompanying this, planetary warming has ceased despite still increasing carbon dioxide emissions. Some solar physicists have issued warnings that strong cooling may be imminent. Has the IPCC revised any of its views as a result? Fat chance.

Professor Chubb also points out the impossibility of waiting for certainty (Godot arrives more quickly) before setting climate policy, and the need for insurance against climate change, two points with which I entirely agree. Good governance on scientific issues is based on the twin principles of prudence and do no harm, especially to society's most disadvantaged. Everything that we know about climate change tells us that it is both dangerous and uncertain. The appropriate insurance is a national policy based on preparing for and adapting to all climate events as and when they happen, irrespective of their cause. Loading If, instead, political pressure from lobby groups defeats contestable scientific advice, then Australia will get a swingeingly expensive, regressive and environmentally ineffectual carbon dioxide tax - and live to regret it. Professor Bob Carter is a geologist, a fellow of the Institute of Public Affairs and author of the book, Climate: The Counter Consensus.