The Effect Of Galactic Cosmic Rays On Earth's Climate = Sweet FA

From Realclimate:

Galactic cosmic rays (GCR) are energetic particles originating from space entering Earth’s atmosphere. They are an important source of ionization in the atmosphere, besides terrestrial radioactivity from e.g. radon (naturally emitted by the Earth’s surface). Over the oceans and above 5 km altitude, GCR are the dominant source. Their intensity varies over the 11 year solar cycle, with a maximum near solar minimum. Carslaw et al. give a nice overview of potential relations between cosmic rays, clouds and climate. Over the first half of the 20th century solar irradiance has slightly increased, and cosmic rays have subsequently decreased. RC has had many previous posts on the purported links between GCR and climate, e.g. here, here and here.

[...]

The authors concluded that this was “far too small to make noticeable changes in cloud properties based on either the decadal (solar cycle) or climatic time-scale changes in cosmic rays.” .... More studies of this kind will undoubtedly come up with different numbers, but it’s perhaps less likely that the qualitative conclusion, as quoted above, will change dramatically. Time will tell, of course.

I've written a couple of times on this topic, although admittedly the technical nature of the subject matter gets to (and beyond) the limits of my comprehension. For example, one theory linking GCRs to climate change argues that increases in solar activity (measured by sunspot numbers) drives an increase in the force/velocity of the solar wind, which in turn sweeps away Cosmic Ray particles that might otherwise reach Earth's atmosphere. Cosmic radiation in Earth's atmosphere drives ionization, which drives low cloud cover (LCC). Thus, high levels of solar activity mean low levels of sunlight-reflective LCC, from which follows an increase in global mean surface air temperatures (Global Warming).

Last year, some research was done last year by U.K. physicists T. Sloan and A.W. Wolfendale; they located short term increases/decreases in CR intensity in existing data sets (Forbush decreases, for example), and looked around for corresponding changes in LCC (low cloud cover) indexes.

They found no such increase. Israeli astrophysicist N.J. Shaviv criticized their work here, and Mr. Sloan was kind enough to respond on this very blog, here.

No Solar Link Redux, Redux

Research has thrown further doubt on the notion that cosmic rays are a major influence on the Earth's climate.

This is very similar to recent work by Sloan and A.W. Wolfendale, which I noted here; its lead author ( Jon Egill Kristjansson) suggests that if a theory like Svensmark's is true (cosmic radiation drives cloud formation drives average temperature increases/decreases on Earth) then

...sudden changes in cosmic ray intensity should ...[produce]... increases in cloud cover, changes in the size of droplets, and possibly in the total amount of water carried in the clouds.

The author(s) see no such changes, therefore conclude that the theory is not likely to be true.

I should note that the first Sloan/Wolfendale paper inspired this critical response from Israeli astrophysicist N.J. Shaviv, which prompted a rebuttal (exclusive to this blog) from Terry Sloan himself.

Yeah, we're about more than fighting Nazis at BCLSB.

On Solar Links: Sloan Responds To Shaviv

Earlier in April, Terry Sloan and A.W. Wolfendale published a paper in which they offered an apparent refutation of Henrik Svensmark's theories linking solar activity to Global Warming. The paper is here, my post on it here. Yesterday, astrophysicist N.J. Shaviv published an on-line critique in which he suggests that Sloan and Wolfensdale have made three mistakes in their paper:

Two arguments are based on the expectation for effects which are much larger than should actually be present. In the third argument, they expect to see no phase lag, where one should actually be present. When carefully considering the link, Sloan and Wolfendale did not raise any argument which bares any implications to the validity or invalidity of the link.

I contacted Terry Sloan yesterday afternoon via email and asked him if he would like to respond to Mr. Shaviv's arguments, and he asked me to post the following:

Dear Shaviv,

I would like to correct the factual errors in your blog.

1. Concerning cosmic rays. Muons, neutrons and the soft component of cosmic rays are all produced from the interactions of the primaries in the upper atmosphere. So the thickness of atmosphere above them is irrelevant. This is a factual error in your paper.

You say we should have compared with ionization chamber data - no such long term data exist either for shielded ion chambers (only sensitive to muons) or unshielded (sensitive to ionization from both muons and electrons). If such data had existed we would have used them.

The Ususkin et al computations of the solar modulation of the total ionization in cycle 22 are compatible with our neutron monitor curve. So our analysis is safe.

2. Your fig 2 from the other Usoskin et al paper is for a highly selected data sample with a large correlation coefficient - not the global average with which we compare. Hence your fig 2 has little to do with our analysis using global averages. We stuck to global averages because in the original Marsh and Svensmark work they computed from the globally averaged dip in cycle 22 that the radiative forcing was 1.4 W m^-2 if all the dip was caused by CR. We set out either to confirm whether the dip was due to CR or not and if not to set a limit on the fraction of it which could come from this source. As we could find no corroborative evidence that it was due to ionization we set a limit. Our limit says that the radiative forcing cannot be more than 23% of 1.4 W m^-2.

3. Forbush decreases - the changes in the CR rate were averaged over the same time intervals as the changes in the LCC - so we have done this correctly and not incorrectly as you imply. The Forbush decreases usually take place over times between days to a month.

Regards, Terry Sloan.