AGW: due to cosmic rays and freons?

Lots of skeptics and the überalarmist Alexander Ač sent me the information about a widely discussed paper

Cosmic-Ray-Driven Reaction and Greenhouse Effect of Halogenated Molecules: Culprits for Atmospheric Ozone Depletion and Global Climate Change (arXiv, PDF)

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WUWT, Google News

written by Qing-Bin Lu, a physicist (mostly biophysicist) at the University in Waterloo, in October 2012. The first detail that seems bizarre to me is the amount of hype surrounding a preprint that's been out for more than half a year. If there were real, active experts who follow what's going on in climatology and if the paper were right and important, they would have known it for half a year and not just now when the paper happened to appear in a journal.

It doesn't seem to be the case so at least one of the assumptions has to be invalid.




At any rate, the author claims that carbon dioxide has been irrelevant for the global mean temperature between 1850 and 1970; in fact, in a statistical analysis, he finds a slightly negative correlation between CO2 and temperature, \(R=-0.05\).

On the contrary, there's a positive claim – a nearly perfect correlation was observed with \(R\geq 0.96\) in 1970-2012 between the global surface temperature and the total amount of freons (more precisely CFCs – "freon" is a brand name owned by DuPont – and even more precisely halogenated gases) in the stratosphere.




So these ozone-hole-related compounds and factors decide about the climate as well, he believes. The Montreal Protocol is being praised; it recovered about 20%-25% of the Antarctic ozone hole while no significant progress has been seen in the mid latitudes. Note that the amount of ozone is reduced by freons but also by the effects of cosmic rays; the latter are modulated by the solar activity, we're reminded.

The author argues that freons could have generated 0.6 °C of warming between 1970 and 2012 and if they're really this important, their expected disappearance in the next 50-70 years could lead to global cooling that would bring the global mean temperature back to the levels people experienced in the 1950s.

There are many graphs in the paper; I won't repost them here. Some of them look pretty convincing. Still, the correlations could be coincidental and this possibility is more likely because many of these correlations have only been verified in the latest 3 decades or so. It's easy to fool oneself. I've seen many rather impressive visual correlations – three or four bumps reproduced rather nicely by a "theory" – and I know that most of them turn out to be fake.

Moreover, this scholar has much more experience with DNA molecules than analyses of the climate. The latter is a rather complicated thing and beginners tend to be naive in many respects. For these reasons and others, I doubt that the global climate is so easily linked to the freons. But I am not quite certain. It's plausible. They're powerful greenhouse gases (thousands of times greater global warming potential than CO2).



Around 0:19, this comedian seemed confused about the difference between "global warming" and "ozone depletion". Maybe he wasn't that confused, after all? ;-)

The apparent observation that no one can really safely show that the paper is wrong and why the paper is wrong highlights the immense degree of uncertainty about the truly dominant climate drivers on the decadal and centennial timescales.