Cosmic rays may be contributing to global warming?

[jmercer]

Well, this is different...

 

[CapelDodger]

It's always worth checking out RealClimate when such claims arise.

http://www.realclimate.org/index.php/archives/2006/10/taking-cosmic-rays-for-a-spin/

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.

As RealClimate comments :

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.

So not particularly different from all the other forlorn hopes snatched at by contrarians.

 

[jmercer]

Ah! Thanks!

 

[Cuddles]

One major problem with this sort of thing is that the effects of clouds really aren't very well understood. Even if cosmic rays really do have a noticeable effect on the clouds, we still aren't sure if more clouds will warm or cool the Earth, so any speculation about global warming is pointless.

 

[CapelDodger]

One major problem with this sort of thing is that the effects of clouds really aren't very well understood. Even if cosmic rays really do have a noticeable effect on the clouds, we still aren't sure if more clouds will warm or cool the Earth, so any speculation about global warming is pointless.

as RealClimate puts it

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!)

This has been a focus of research for quite some time, still with no definitive results. We all know cloudy nights tend to be warmer than clear nights (especially those who've spent time in a desert), and cloudy days tend to be cooler than sunny ones. The warming effect continues day and night, while the cooling effect is daytime only. It's a tricky one.

(A Global Warming thread and not even a glint of Diamond? This has to be a slam-dunk loser. )