Climate change denial websites immediately jumped all over a recent paper from the CERN CLOUD project, about the effects of cosmic rays on cloud formation.

I knew they had jumped, actually, before I even read “Watts Up With That” or any of the other blogs dedicated to discrediting climate science, because my email Inbox was suddenly full of gloating notes from anonymous right wingers, as it always is when one of these hysterical climate denial outrages happens. For example, on Friday someone used the fake email address “AGW@myass.com” and the subject “you’re a dipwad,” to send the URL of this article at the Register: CERN: ‘Climate models will need to be substantially revised’.

I didn’t write about this story immediately because 1) atmospheric aerosol nucleation isn’t really my specialty, and 2) I wanted to wait for the inevitable debunking of the overhyped denialists’ claims by a real scientist.

And here it is, with more than you ever wanted to know about the role played by ionization in nucleation: RealClimate: The CERN/CLOUD results are surprisingly interesting…

Aerosol nucleation experiments are not usually front page news, and the likely high public profile of this paper is only loosely related to the science that is actually being done. Rather, the excitement is based on the expectation that this work will provide some insight into the proposed cosmic ray/cloud/climate link that Svensmark (for instance) has claimed is the dominant driver of climate change (though note he is not an author on this paper, despite an earlier affiliation with the project). Indeed, the first justification for the CLOUD experiment was that: “The basic purpose of the CLOUD detector … is to confirm, or otherwise, a direct link between cosmic rays and cloud formation by measuring droplet formation in a controlled test-beam environment”. It is eminently predictable that the published results will be wildly misconstrued by the contrarian blogosphere as actually proving this link. However, that would be quite wrong.

We were clear in the 2006 post that establishing a significant GCR/cloud/climate link would require the following steps (given that we have known that ionisation plays a role in nucleation for decades). One would need to demonstrate:

1. … that increased nucleation gives rise to increased numbers of (much larger) cloud condensation nuclei (CCN)
2. … and that even in the presence of other CCN, ionisation changes can make a noticeable difference to total CCN
3. … and even if there were more CCN, you would need to show that this actually changed cloud properties significantly,
4. … and that given that change in cloud properties, you would need to show that it had a significant effect on radiative forcing.

Of course, to show that cosmic rays were actually responsible for some part of the recent warming, you would need to show that there was actually a decreasing trend in cosmic rays over recent decades – which is tricky, because there hasn’t been (see the figure).