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Time to question the received wisdom on climate change?


The UK government, having boldly gone where no other government has been before and introduced a regime of legally binding emissions cuts, has now accepted the Committee on Climate Change’s recommended carbon budget for 2023-27. This goes beyond what other EU Members States are committed to, and was achieved despite some public opposition from ministerial ranks. The belief is that a threat from Greenpeace to try for a judicial review if the committee’s recommendation was rejected may have tipped the balance: this was one risk that the Coalition could well do without at present.

The decision is tempered by a review being scheduled for 2014, as a sweetener for those (including Vince Cable) who fear for the competitiveness of UK industry if the rest of the world fails to follow Britain’s lead. Politics being the art of the possible, it is quite likely that the final decision was in effect a way to reduce the flak from the green lobby, while leaving enough wriggle room to keep internal critics on side, without there being an intellectual commitment to the underlying scientific advice. Or it could be that David Cameron and colleagues genuinely buy into the currently received wisdom from the IPCC.

If so, they will not have been swayed by the refusal of the global climate to work in the way the way that computer models predict. Temperatures have remained pretty level since the turn of the century, with mainstream climate science failing to come up with any credible explanation. At heart, the argument rests on a single ‘fact’; that only the enhanced greenhouse hypothesis is able to explain the pattern of warming during the twentieth century. Others – sceptics, realists or ‘deniers’ depending on your world view – have repeatedly questioned this assumption, but have as yet failed to provide hard evidence that any other mechanism may also be at the root of the pattern.

That now seems about to change. There have been various theories advanced relating to the influence of solar variability. After all, essentially all the thermal energy the Earth receives is by way of radiation from the Sun, so this seems like a good place to start. One particularly intriguing suggestion has been championed by Henrik Svensmark and Eigil Friis-Christensen of the Danish Space Research Institute, who suggested in 1997 that the Sun might have an indirect effect on cloud formation and thus average temperatures.

According to this hypothesis, high energy cosmic rays may penetrate the atmosphere to a depth sufficient to cause nucleation of water vapour and hence cloud formation at low-level. But the constant stream of cosmic rays is mediated by the solar wind, a variable flow of atomic particles from the Sun which partially deflects the incoming radiation. When this is strong, fewer cosmic rays reach the Earth, which results in fewer clouds and hence higher temperatures because more solar radiation hits the ground. Conversely, if the solar wind is weak, the greater flux of cosmic rays causes more clouds to form, which reflect more sunlight and reduce temperatures.

Of course, it’s not quite as simple as that, but those readers who would like to learn more can do so in an admirably clear and accessible book by Svensmark and his co-author, Nigel Calder, called The Chilling Stars – A new theory of climate change. But the Svensmark hypothesis has remained controversial, since it calls into question the very basis of the IPCC’s efforts and, more particularly, the policy of reducing carbon dioxide emissions to mitigate climate change. It has not found widespread acceptance, but now supporting evidence is starting to make it impossible to ignore.

In 2007 (also the year that The Chilling Stars was published) the results of an experiment in Copenhagen called SKY were published by the Royal Society. This was the first controlled demonstration of the ability of gamma rays (in this case, highly penetrating muons which create bursts of electrons) can rapidly induce formation of aerosols in air containing water vapour and a naturally occurring low level of sulphuric acid. But this was not enough to convince proponents of the anthropogenic global warming hypothesis that there might be an alternative explanation for climatic variation.

One criticism of the original SKY experiment was that the source of particles (penetrating gamma radiation) was not the same as cosmic radiation. But now collaborative work between scientists at the University of Aarhus and the Danish National Space Institute has gone further and used high energy particles generated by an accelerator to achieve the same effect (see Scientists at Aarhus University (AU) and the National Space Institute (DTU) show that particles from space create cloud cover). The high energy electrons created in this way are much more akin to natural cosmic rays, and the fact that they show the same ability to create aerosols strengthens the case that the Svensmark hypothesis is worth further study.

The release from Aarhus University is quite clear:“New input to the United Nations climate model: Ulrik Ingerslev Uggerhøj, Physics and Astronomy, AU, along with others including Jens Olaf Pepke Pedersen and Martin Bødker Enghoff, DTU Space, have directly demonstrated in a new experiment that cosmic radiation can create small floating particles – so-called aerosols – in the atmosphere. By doing so, they substantiate the connection between the Sun’s magnetic activity and the Earth’s climate.”

Predictably, there has been little publicity for the new findings and no renewed public questioning of the current received wisdom. But that may change later this year when the first results come from a major experiment at CERN called CLOUD. This will use a much larger chamber and be able to generate even more data on the effect of various types of particles on aerosol and cloud formation. If the results are consistent with those obtained in Aarhus, then they will be impossible to ignore. Readers may be interested in following Nigel Calder’s updates on the issue.

Not that this conclusively ‘proves’ the Svensmark hypothesis, but it certainly provides hard evidence that the proposed mechanism is right. This means that, on one hand, we have a plausible hypothesis (the enhanced greenhouse effect) which has no hard supporting evidence but the belief in which is based on the outputs of computer models, while on the other hand we have an alternative hypothesis which is equally plausible and which is supported by hard evidence. The IPCC and governments simply cannot continue to be blinkered. Failure to take this seriously could take the developed world up the biggest policy dead end in history.