Browsing through the blogosphere recently, I came across an interesting little story about the scientific method, scientific progress, and un-scientific spin (h/t Hank Roberts). The subject concerns the polar ozone hole in Antarctica and a possible role for cosmic rays in its variability on solar cycle timescales. The proponents of this link are a small research group at the University of Sherbrooke in Canada, who find themselves up against the mainstream stratospheric chemistry community and whose ideas are twisted out of all recognition by the more foolish of the usual suspects.
The story hit the ‘tubes earlier this year when researcher Q.B. Lu predicted that this years Antarctic ozone hole would be the biggest ever due to the actions of increased galactic cosmic rays (GCR) (because we are at solar minimum and GCR are inversely correlated to solar activity). This years peak ozone hole has now come and gone, and the prediction can therefore be evaluated. Unfortunately for Dr. Lu, this year’s hole was merely about average for the decade – a result that wasn’t too supportive for his theory.
This story made me a little curious about this though. Firstly, I didn’t initially understand why cosmic rays should be playing a role in ozone depletion – most of the cosmic ray effects that are usually discussed revolve around cloud-aerosol connections, but there are not many clouds in the stratosphere where the ozone holes form, and the ones there are (Polar Stratospheric Clouds – PSCs) are much more sensitive to temperature and water vapour than they are likely to be to background aerosols. On further investigation, it turns out that this idea has been out there for a few years (and was reported on then) and has subsequently been discussed in the ozone literature.
So let’s start with the background theory. Standard (Nobel-prize winning) stratospheric chemistry has tied ozone depletion to the increasing chlorine (Cl) load in the stratosphere which catalytically destroys ozone and comes from the photolytic dissolution of human-sourced chloro-fluoro-carbons (CFCs) high in the stratosphere. In the polar night, the presence of PSCs allows for a specific class of heterogeneous Cl reactions to occur on the surface of the cloud particles which turn out to be very efficient at destroying ozone. Hence the presence of an ozone hole in the very cold Antarctic polar vortex. Since PSCs are very sensitive to temperature, cold winter vortex conditions often presage a large ozone depletion the following spring (note that polar ozone depletion only occurs in sunlight and so is a spring time phenomena in both hemispheres). This is pretty much undisputed at this point (well, at least by serious scientists). We here at RealClimate even used this relationship to predict (successfully) a particularly large Arctic ozone depletion event in 2005.
Dr. Lu’s theory though posits an additional mechanism to release the Cl from the CFCs – and that is through GCR effects. Specifically, Lu suggests that the action of the GCR on CFCs attached to PSCs causes more Cl to be released, thus potentially delivering more Cl exactly where it could enhance polar depletion most effectively. The evidence for this comes from correlations of ozone loss with GCR (over a couple of solar cycles) and some suggestive lab experiments. Note that this does not call into question the anthropogenic source of the Cl which is still from CFCs.
However, Lu and colleagues’ theory has been strongly challenged in the literature. For instance, here, here and here. The comments focus on two main aspects, the weakness of the correlations (see figure), and the ancillary evidence that there isn’t any obvious evidence for CFC destruction in the polar vortex itself. In fact, correlations of CFCs with air mass tracers from the upper stratosphere are very stable, indicating that the photolytic conversion of the CFCs is by far the dominant source of Cl. These rebuttals seem quite compelling, and there doesn’t seem to be much continued support for Dr. Lu’s GCR idea. However, Lu is still pushing it (hence the press release this year just weeks before the prediction would be put to the test). One might think Dr. Lu’s ideas wrong, but one can’t fault his bravery in putting them to the test.
As we stated above, the un-exceptional ozone loss this year pretty much undermines the correlations that were at the heart of Lu’s idea. Thus I predict that this is unlikely to be discussed very much more in the literature except as an example of how interesting ideas are generated, discussed, tested and (in this case) found wanting. This indeed is how scientific progress is made.
But, as has often been noted, the contrarian-sphere is a world on its own. It was inevitable that the headline link between GCR and ozone holes would entice the old-school ozone depletion skeptics and ‘everything-is-solar” proponents out of their burrows. Tim Ball led the charge. Now Dr. Ball is a long time skeptic on the human influence on ozone depletion as well as climate change, and so he couldn’t resist the occasion to opine on all theories anthropogenic:
Nurtured by environmental hysteria and the determination to show all changes in the natural world are due to human activity, the claim CFCs were destroying ozone jumped directly from an unproven hypothesis to a scientific fact.
He also includes standard statements implying that scientists implicated CFCs in ozone depletion to deprive the developing world of refrigeration (oh my!), how there hasn’t been a change in ozone depletion in any case (despite showing a series of figures obviously demonstrating this – see here as well) and so on…. He did however note that Dr. Lu’s theories don’t actually change any of the mainstream prescriptions for dealing with ozone depletion (though he does get confused about the CO2 impact on stratospheric temperatures – it makes them colder, not warmer). But the real prize goes to Dennis “unstoppable” Avery who suggests that Dr. Lu’s theories will confirm a link of GCR to climate change:
If the South Pole gets an ozone-hole maximum in the coming weeks, it will strengthen the case for cosmic rays, and endorse a Modern Warming driven by solar variations rather than human-emitted CO2.
This is the same logic as assuming that because salt makes food taste better, throwing it behind your shoulder must bring luck. That is, they are just not connected. And I’m pretty sure he won’t accept the logical corollary. Needless to say this is a very feeble grasping at straws. But to quote a recent Monbiot article:
There is no pool so shallow that a thousand bloggers won’t drown in it.
Nor an ozone hole it seems either.