Contrary to the 'natural' view, scientists are 90 per cent sure that human activity causes global warming, argues Prof Ray Bates.
Nigel Calder is quite right in stating in his interview that progress in science often depends on new ideas that challenge the prevailing consensus. It is because of this fact that research scientists are trained to be sceptical and to question all orthodoxy within their own specialised fields. To question accepted views, however, is risky, and scientists who embark on this course must be very sure of their ground. In the normal course of events, new results in science are submitted as papers to scientific journals where they are subjected to a process of anonymous peer review before a decision on publication is made. Opposition to new ideas that challenge the accepted ones is normal, but generally progress will be seen for what it is and the scientists involved will in time receive due recognition.
What is unusual in the present instance, where Dr Henrik Svensmark and his co-workers in Copenhagen are proposing new ideas regarding the effects of solar variations on climate, is the extent to which, from an early stage, the ideas in question have been championed in the public domain. Nigel Calder has, for the past 10 years, been extolling Svensmark's work, beginning with his popular book The Manic Sunin 1997, continuing with a programme on BBC TV a few years later, and now with a new popular book, The Chilling Stars, co-authored with Svensmark himself. Calder also played a prominent part in the recent Channel 4 TV programme The Great Global Warming Swindle.
As is to be expected from a science writer of Calder's talents, the new book is brilliantly written for a popular audience. It tells a gripping tale of how a new scientific theory has emerged and of its implications for climate change, not only at the present day, but over the span of human history and into the distant geological past. The book also exhibits Calder's formidable rhetorical skills in advocating the view that attributing the present-day global warming to man-made greenhouse gases is a falsehood propagated by political interests.
The main scientific plank on which the new book is based is an experiment called Sky (the Danish word for cloud) carried out by Svensmark and his colleagues, which shows how ions produced by galactic cosmic rays can promote the formation of small particles in the atmosphere that may go on to form cloud condensation nuclei; the experiment has been explained in non-technical terms by Calder in his interview. The results of the experiment have been published in a recent paper in the prestigious journal Proceedings of the Royal Society. The paper clearly demonstrates that Svensmark and his colleagues are talented physicists. The paper shows all the signs of having gone through rigorous peer review: it is measured, meticulous, and tentative in claiming that the results have any implications for climate change.
In the popular book, on the other hand, all restraint has been abandoned. Here, cosmic rays are presented as explaining almost all aspects of climate change, past and present, and the idea of greenhouse gases playing any role is essentially dismissed.
Calder calls for open debate on this issue in the scientific tradition. There has already been much debate in the scientific forums, where many serious objections have been raised to the cosmic ray theory. It might be better if the debate were confined to these forums until some kind of consensus has been reached among the professionals. Since the issue has now become a matter of public discourse, I will offer my contribution to the debate by posing here a sample of the questions I would have raised in privacy if The Chilling Starshad been condensed to a paper for a scientific journal and sent to me for review.
(a) The cosmic ray mechanism is supposed to act by changing the amount of sunlight reflected to space by low-level clouds. It should therefore predominantly affect daytime rather than night-time temperatures (there is no sunlight at night). The observations for recent decades, however, show that night-time and daytime temperatures have been rising at about the same rate. How can this discrepancy with the cosmic ray theory be explained?
(b) The cosmic ray mechanism is supposed to act mainly over the oceans, where, according to the theory, there is an abundance of sulphates that can be induced by cosmic rays to form cloud condensation nuclei. The observed global warming, however, is more accentuated over land than over ocean. How can this discrepancy be explained?
(c) The acid test, according to the authors, is the observed cooling over East Antarctica, which they claim can be explained by the cosmic ray theory. In the explanation offered, however, no reference is made to the fact, explicitly admitted in the paper describing the Sky experiment, that the results of the experiment apply, at best, to water clouds and do not cover ice clouds. With this taken into account, how can the results of the experiment explain anything that happens over the frozen wastes of Antarctica?
If these questions were not answered satisfactorily, I would not, as a reviewer, recommend publication of the supposed paper.
The public undoubtedly needs to be informed about progress in climate science. It should regard with caution, however, the public advocacy of new scientific theories before these theories have gained any significant degree of acceptance in the world of the professionals.
In my view, the Intergovernmental Panel on Climate Change (IPCC) provides the most authoritative source of information on climate change. Its recent statement on global warming should be regarded as the most reliable scientific statement informing the political debate.
Ray Bates is adjunct professor of meteorology at UCD. He was formerly professor of meteorology at the University of Copenhagen and a senior scientist at Nasa's Goddard Space Flight Centre.