What is the proper role of scientists in public debate? What is the proper use of scientific evidence in public policy and administration? These questions have themselves become matters of public debate and issues of concern to scientists in defining their professional responsibilities. This perspective statement aims to clarify the issue and dispel some confusion surrounding these questions. If we have sound reasons for the position on scientific responsibility that we advocate, then we believe it will mark a major advance in understanding the professional responsibilities of scientists.

A typical and important example of the confusion over the professional responsibility of scientists that we wish to identify and resolve is provided by an article over the role of scientific dissent in the debate on global warming, written by Matthew Warren, Environment Writer for The Australian newspaper (The Weekend Australian, March 17-18: 19, 26). Warren makes some revealing observations: ‘Science by its very nature is an argument' (19, paragraph1, line 7); ‘The debate over climate change has become increasingly stifling and intolerant to dissenting voices, as the mainstream position has become more secure' (19, para. 2, l. 10); ‘"That's a very funny procedure by most standards" [Lindzen] said. "You don't appeal to consensus if you have a scientific argument"' (19, para. 4, l. 43); ‘We have agreed the issue is too important to wait for more conclusive answers, that we are prepared to act comprehensively on climate change, possibly at considerable cost, on the trust that most respected, credible scientists are deeply concerned about the seriousness of this threat.' (26, para. 3, l. 19).

Warren is clearly concerned that scientific dissent is being suppressed, contrary to the internal standards of scientific enquiry itself. He is also concerned that dissent is now being ignored in practice in the public policy debate over global warming. Warren's concerns may appear to accord with the scientific ethos. This demands that scientists not be subject to suppression of their findings. The most notorious example of suppression in the history of science is the case of Galileo, who was ordered by the Pope to recant his belief in Copernicus' doctrine that the Earth revolved around the Sun, or be subject to the Inquisition. Galileo is reputed to have whispered "but yet it moves" after declaring, as required by the Pope, that the Earth is the centre of the universe.

It is now universally accepted that Galileo should have been entitled to challenge the conventional Ptolemaic wisdom that the Earth was the centre of the Universe, with the Sun and other heavenly bodies circling it. That entitlement is not conditional on decisive evidence in favour of his position: it stands regardless of whether Feyerabend (1975) is correct in his view that Galileo did not have decisive empirical evidence in favour of the Copernican hypothesis when he published his Dialogue on the Two Chief World Systems (1632). Nor should Galileo's entitlement to free expression of scientific opinion be diminished by the fact that his arguments were not purely scientific, as that is understood today, but included philosophical arguments as well. As Warren suggests, tolerance of dissenting opinion is now an essential feature of scientific enquiry. It is also an essential part of a liberal political philosophy that the expression of scientific opinion be free of political or social coercion, as Mill argues in On Liberty (  ).