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:

First, the particles observed in these experiments are orders of magnitude too small to be Cloud Condensation Nuclei (CCN). In the press release, this is why they talk about the ‘building blocks’ of CCN, however, aggrandisation of these small particles is in no sense guaranteed (Missing step #1). Secondly, the focus is on low clouds over the ocean. However, over the ocean, there are huge numbers of condensation nuclei related to sea salt particles. Thus to show that the cosmic ray mechanism is important, you need to show that it increases CCN even in the presence of lots of other CCN (Missing step #2). Next, even if more CCN were made, you would need to show that this actually changed cloud cover (or optical thickness etc.) (Missing step #3). And given that change in cloud properties, you would need to show that it had a significant effect on radiative forcing – which despite their hand waving, is not at all well quantified (even the sign!) (Missing step #4). Finally, 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) (Missing step #5). All of this will require significant work and there are certainly no guarantees that all the steps can be verified (which they have been for the greenhouse gas hypothesis) – especially the last! However, they would seem essential to justifying the claims in the press releases.

Will these results be a spur to future research? Possibly. But the ridiculous spin put on this paper is liable to continue to put off mainstream scientists from pursuing it. It’s as though Svensmark and co. want to enhance the field of solar-terrestrial research’s bad reputation for agenda-driven science.

Unsurprisingly, this paper was trumpeted throughout contrarian circles last week and was received uncritically (with one honorable exception in the ‘climatesceptics’ discussion group), even by people who normally spend their time decrying science-by-press-release. (A word to the wise, consistency goes a long way to establishing credibility…).

At RealClimate, we’ve often criticised press releases that we felt gave misleading impressions of the underlying work and lead to confused, and sometimes erroneous, headlines, but this example is by far the most blatant extrapolation-beyond-reasonableness that we’ve seen. If this group wants to be taken seriously and interact constructively with the rest of the community (which is the only way the ‘missing steps’ will get sufficient attention), they have to act in a serious manner, be honest about the problems and caveats, and resist the temptation to speculate beyond what is justified. The kind of antics seen in this case may play well for the peanut gallery, but they won’t impress the critics.