Taking Cosmic Rays for a spin

In 1859, John Tyndall’s laboratory experiments showed that water vapour and carbon dioxide absorb infra-red radiation and that they could therefore affect the climate of the Earth. As soon as his paper was published (1861) in the Proceedings of the Royal Society, he put out a press release for the London newspapers explaining that this result implied that all past climate changes were now understood and all future climate changes could be predicted simply from a knowledge of the concentrations of these ‘greenhouse’ gases…

Fast forward to 2006: Svensmark and colleagues’ laboratory experiments show that highly ionizing radiation can create ultra-small aerosol particles. As soon as the paper is published in the Proceedings of the Royal Society, they put out a press release for the world’s newspapers explaining that this result implied that all past climate changes were now understood and all future climate changes could be predicted simply from a knowledge of the intensity of these ‘cosmic rays’….

History repeating itself? Well, not exactly. Tyndall actually restricted himself to describing his experiments and simply linking it to the work of Fourier a few decades earlier. It took more than another century before the credible quantitative estimates of these effects and their influence on past and possibly future climate were made, along with good enough observations of the gases to know that they have (and continue) to change significantly. However, Svensmark and colleagues, not wanting to wait for the credible quantitative results to come in, instead short circuited all of that tedious follow-up work, scaling up to realistic conditions, theoretical and modelling studies demonstrating that their effect was indeed viable, and simply declared in their press materials that the team had ‘discovered that cosmic rays play a big part in the everyday weather’ and ‘brings to a climax a scientific quest that has lasted two centuries’. Nobel prizes all round then.

Alas! if only it were that simple….

(In explaining why it isn’t, I should first apologise for the third solar related posting in as many weeks. I realise that most people are not that interested and so after this one, I promise a moratorium for a month or so!)

Svensmark’s paper itself is indeed of some interest. Aerosol processes are among the most uncertain, and most studied, aspects of climate and these experiments (they bombarded a clean mixture of water, SO2, O3 and air with high energy UV and saw small H2SO4 droplets form) might be useful in adding to that field. One could quibble with the use of the high-energy UV (which never penetrates to the lower troposphere), and the high concentrations of SO2 and O3, but by far the biggest problems lie in the study’s relevance to the real world atmospheric conditions.

The working hypothesis of the cosmic ray crowd is that the (weak) correlations between low clouds and cosmic rays are causal (i.e. a cosmic ray increase – due to a solar magnetic field weakening – causes low clouds to increase, cooling the planet). The ‘spin’ on this new paper is that this has been demonstrated, and is significant, and furthermore, is responsible for the 20th Century rise in global temperatures. But let’s look carefully at what is required in this logic:

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