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Galactic cosmic rays: Backing the wrong horse

Posted on 24 September 2011 by muoncounter

The popular press is still pushing the preliminary CERN CLOUD results as proof that galactic cosmic rays (GCRs) are a major influence on climate. We've already had an excellent rebuttal here on SkS, featuring Jasper Kirkby's own words urging a more sober interpretation of his preliminary results.  Yet those who do not fully understand the science are willing to bet that they have proof positive of the GCR-climate connection.  Here is another look at the science of cosmic rays, in which we find out that's not a very good bet.

In horse racing, there's a payout for the 1st, 2nd and 3rd place finishers.  All the other horses in the race finish 'out of the money.'  One way to go broke very quickly is to repeatedly back the wrong horse.




Let's Check the Odds

The GCR-climate connection is based on well known science:  cosmic rays do indeed contribute to ionization of the earth's  atmosphere (known as CRII, for cosmic ray induced ionization).  Whether CRII leads to enhanced cloud formation is the basic conjecture that GCR supporters want to establish.  They must then show that GCR-induced clouds (if any such exist) in turn produce observable climatic effects. 

If this is to be a horse a race, we must examine the field of entrants and study their track records.  The full family of particles observed when an energetic primary GCR particle enters the atmosphere is illustrated below.

-- source

The CERN CLOUD experiment uses a positive pion beam of 3.5 GeV energy, a relatively middle-of-the-road energy on the spectrum of GCRs.  Thus CLOUD backs only one horse in this race: the right-most interaction, pions (π) decay to muons (µ) and neutrinos (ν); note that this interaction does not produce neutrons and is thus invisible to neutron monitors around the world.  What of all the other particle interactions on the diagram above?  Which horse is the favorite in this race?

Picking a Favorite

Cosmic ray particles sourced by the sun are  known as Solar Energetic Particles (SEPs) -- these are typically fast-moving solar wind protons.  The energy associated with SEPs runs as high as 5 GeV, equivalent to a flux of  3x10-6 to 2x10-5 W/m2.  Those on the lower end tend to penetrate only the upper atmosphere; these are the events that can lead to Forbush Decreases (FDs).  Even higher energy SEPs can lead to significant increases in particle count rates at the earth's surface known as Ground Level Enhancements (GLEs).  These events produce the additional particles shown in the illustration above; we do indeed see these events on neutron monitors. 

The image below is a composite of neutron monitor records, illustrating the distinction between the appearance of FDs and GLEs.  FDs have been observed as precursors to GLEs.  In this example, the count rate multiple is approximately 25%, so the GLE is not particularly energetic.

FD and GLE

-- source

Usoskin et al 2009 investigated ionization by GLEs (emphasis added):

"There is a strong correlation between the GLE magnitude (in Neutron Monitor %) and the ionization effect in the stratosphere ... – all strong GLEs led to a more than 10% enhancement of CRII in the polar region. There is still some weak relation in the upper troposphere ... – all strong GLEs lead to a slight positive ionization effect.  ...

SEP play a role in the ionization only in the upper-middle polar atmosphere. In all other regions the ionization is suppressed due to the accompanying Forbush decrease. ... There is no ionization effect at mid- or low-latitudes, even for the strongest events. It is clear ... that there is no straightforward relation between the strength of GLE (as measured by neutron monitors) and the ionization effect in polar atmosphere. The net atmospheric ionization effect is defined by an interplay between the SEP event itself and a Forbush decrease, which often accompanies it."

That last statement is key to understanding just how difficult it is to establish a cosmic ray-climate connection:  Not all cosmic ray increases ionize the atmosphere.  This horse race went from a walk in the park to a long, slow steeplechase on a very muddy field.

Jumping the Ionization Hurdle

Many GLEs originate as X-class solar flares and are thus relatively rare.  The neutron monitor at  Oulu, Finland observed  55 GLEs during the 50 year period 1960-2010. The neutron count rate increased by more than 10% in only 21 of these recorded GLEs.  One of the largest occurred on 20 Jan 2005, as reported by a number of authors.  From Bieber et al 2005,

"Within a 6-minute span on January 20, 2005, the count rate registered by a neutron monitor at the sea level station of McMurdo, Antarctica increased by a factor of 30, while the rate at the high-altitude (2820 m) site of South Pole increased by a factor of 56."

Inuvik and Fort Smith, Canada reported count rate multiples of 4-5; at Oulu the increase was 269%.   High multiples of the background count rate persisted for several hours.  Per Moraal et al 2008, the protons in this GLE contained a spectrum of energies from ~1.5 - 5 GeV; they also reported that the GLE was composed of at least 3 distinct pulses of particles arriving at the surface of the earth (the first of which caused a Forbush Decrease).  Mironova et al 2011 looked at ionization due to this GLE (emphasis added):  

"The very high level of neutron monitor count rate increase implies that the ionization of the polar atmosphere was dramatically increased during the event ... the calculated ionization due  to the SEP event of 20 January started dominating over the GCR ionization already at 10-km altitude and reached its maximum at about 30 km altitude.  In particular, the CRAC:CRII model calculations suggest that the SEP event produced additional ionization in the polar atmosphere in the altitude range 12–23 km, with the number of ions being greater by a factor of 3–30 than the averaged GCR-induced daily ionization in January 2005." 

Mironova also looked for atmospheric effects due to this GLE (emphasis added):

"We would like also to emphasize that the observed atmospheric effect for this extreme GLE event was barely significant. No clear atmospheric effect was found beyond statistical fluctuations for the weaker SEP event of 17 January 2005, which is a typical SEP event. This implies that only extremely hard-spectrum (high energy) GLE/SEP events can produce a noticeable direct effect on aerosols in the polar low-middle stratosphere."

Thus one of the strongest known GLEs, producing much more ionization than the typical GCR, had no direct affect on the weather - and the sum of many such events will have no connection to climate

In this horse race, until the CLOUD experiment can clear the ionization hurdle by investigating the complex relationship between FDs and higher energy GLEs, it will continue to be tripped by this hurdle and always finish out of the money. Those who've put their money on CERN CLOUD finding a GCR-climate connection are backing the wrong horse.  




Note:  Revised 9/24/2011

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Comments 101 to 127 out of 127:

  1. So Eric, in light of this discussion can we assume that you now agree that GCR remain a dead duck? And short of new evidence (as opposed to speculation) that provides a better model than current thinking, policy should be informed by conventional understanding of climate?
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  2. Lucky for me, Dr. Laken took part of his evening to explain the TSI-GCR link. Over the long run an active sun means more TSI and an active sun means less GCR (due to more solar wind). The measurements of solar activity are smoothed and somewhat qualitative sunspot counts and TSI and GCR are running averages or proxies. Everything works the way I thought. But on a timescale of days the TSI relationship to GCR is complex due to positioning of the sunspots and other features and the movement of those features. So TSI and GCR (and solar UV) have more complex relationships including time delays. The wording in the abstract refers to those short term relationships (because that is what the paper is about).
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  3. scaddenp, GCR was always a dead issue to me for explaining current warming. Now it is less clear to me over the long run also. I am however still interested in GCR due to its potential modulation of water vapor feedback. What I would like to see is a study examining uncertainties in climate sensitivity due to uncertainties in GCR.
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  4. You can get sensitivity directly from model, or you can get sensitivity from empirical methods from past climate events. In the former, its pretty hard to see how you could change sensitivity because you have to have physics to add GCR into climate. Lacking evidence or proven mechanism, then that is pretty hard. For empirical methods, then effectively GCR is already included because there is no way to sort out different factors in such studies without a model.
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  5. And as an observation, you seem to still engaged in trying to find evidence for low sensitivity which you appeared to decided is likely a priori rather than from evidence in front you.
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  6. Either the GCR needs to be added to model physics or it will have to be ignored. Very short term empirical analysis, although still requiring a model, should not need GCR included as we see from the Laken and other papers. For solar cycle sensitivity-based estimates, I don't see how GCR can be ignored if it has any role at all. For longer term empirical it probably needs to be in the model.
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  7. 106, Eric, Except GCR can't be added to the model physics because no one has demonstrated a working mechanism and defined the underlying physics needed to incorporate it into a model. By contrast we know the exact bands at which CO2 absorbs radiation, the emission times, the density throughout the atmosphere, the overlap with other gases, the resulting TOA emissions spectrum, the energy associated with each photon, and 80 bazillion other details that allow us to directly model the physics. For GCRs we have "hey, look, there was maybe sort of a correlation over a several million year time scale, given a window of tens of millions of years, give or take, and a questionable proxy for the strength of GCRs, and no correlation whatsoever in recent, hard, direct instrumental measurements." GCRs are a non-starter until someone does a lot more work and gets some positive results from it, and I don't expect that to happen for a decade at least, if ever. Including GCRs now might as well be accompanied by the well-considered effects of Eurasian Leprechaun Farts (ELFs, a well-known Christmas time seasonal impact).
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  8. Eric#103: "I am however still interested in GCR due to its potential modulation of water vapor feedback." As we've seen, the most recently published results consist of Dragic, Love 2011 and Laken, all reporting that this 'potential modulation' is either minimal, undetectable or non-existent.
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  9. Eric, GCR does not need to be added to anything, as there is still, despite many requests, no mechanism for how it would operate. Cute model pirate ships don't need to be added to the models either. Others have already said the mercurio is junk science and should not be relied upon, one last example is he does not suggest the primary hypothesis for the PDO, that it is simply the integrated result of ENSO (Newman et al 2003). You keep saying 'potential' this, 'possibly' that in relation to GCR, but the reality is there's nothing there to hang your hat on. Sphaerica has it right above.
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  10. Thanks for the replies. Sphaerica, GCR can't be easily modeled but like you say that's not permanent. Other factors like solar UV will eventually get better modeling too. Perhaps after that we will start to understand weather variations better (though not likely predict). Muoncounter those Forbush decreases are minimal in number but we are in a relatively low GCR period so the decreases may not be as effective since we in an interglacial with relatively less GCR to begin with. Skywatcher, I agree that Mercurio's paper has a lot to be undesired. I thought the 140k year chart (fig 13) was sufficient for a study, but instead of analyzing that in depth, he put in enough ideas for 10 more studies. I think muoncounteri is right that the effects are too minimal to be of consequence to climate over short time periods, certainly including temperatures in 2100. The remaining issue IMO is glacial (mostly high GCR) to interglacial (consistently low GCR) differences since those affect studies that require knowing how each quasi-stable state is produced. It seems to me that Mercurio section 13 was a good start to that, then he goes on in section 14 to talk about global warming "hysteria" and I am forced to toss the whole paper.
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  11. Okay, Eric, and you once again impress as being the honest skeptic.
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  12. scaddenp, I have biases (what I consider intuition) like you say in 105 towards (among other things) low sensitivity, but that's another thread. I also realize that I'm not going to make the perfect case for any of these skeptic arguments, there are people with more knowledge about the topics. But I'll accept your complement for this topic.
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  13. Eric#110: "we are in a relatively low GCR period so the decreases may not be as effective" May I remind you, in 2009: Cosmic rays hit space age high And that was measured by the ACE satellite at the L1 point, where no atmospheric ionization gets in the way. FDs would be plenty noticeable. The problem for GCR adherents is that there just aren't enough of them. That's no doubt why the CLOUD experiment design straddled the energy line between solar cosmic rays and GCRs. But if you say solar cosmic ray flux modulates clouds, then you're still stuck in the high solar activity-> fewer clouds -> warming trap. Picking that warming signal out from the high solar activity warming is a tiny needle in a very large haystack.
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  14. muoncounter, true about the space age but looking back further
    we seem to be at relatively low level of cosmic rays, with the caveat that there is no clear connection to climate in the period above, nor evidence of strong physical mechanism as we discussed in this thread. (source of graph is Beer et al 2006 - having trouble linking)
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  15. Eric, Here's another version of a similar graphic: -- source It's difficult to tell if Be10 is that much lower now then in the past; at these scales, the short-term noise is larger than most of the long term variation. I found this Beer slide presentation; the 14th page after the title has another Be10 graph. The lowest points are roughly 48ka, 30ka, 22ka and 2ka. He cites a paper by Muscheler et al in EPSL 219, which I haven't gone after, as the source of that data. I don't see how this line of inquiry, without a mechanism for a climate connection to cosmogenic radioisotopes, helps one way or the other.
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  16. muoncounter, Dr. Laken kindly responded to more of my questions and suggests caution in reading a lot into long term changes in GCR flux, too many unknowns in the relationship to clouds over those timescales. He also cautioned on Dragic's selection of GCR events. In the Lakin paper they selected using TSI criteria that were designed to preclude bias in event selection. Dr Laken also questioned the use of Diurnal Temperature Range rather than direct cloud measurements, and he might have a point there, but personally I'm not sure what is wrong with DTR which is a localized climatological response.
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  17. 116, Eric, DTR is also strongly influenced by other GHGs, so you have a confounding factor involved.
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  18. Spharica, that is true, but not for the Dragic study because it only look for a DTR response a few days after the cosmic ray event.
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  19. 118, Eric, Sorry, yes, you are correct. My bad.
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  20. Eric, Dragic used DTR because it was something they could quantify and measure. See the comments and quoted section here. It is not that they 'only look for a DTR' a few days after the FD; that's when the DTR change showed up. The unanswered question is why it takes a few days; another example of the weakness of this whole idea.
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  21. The solar flare series of early-mid March has produced a Forbush decrease on the order of 10% at Oulu for several days. This fits Dragic's detectability criteria and should thus result in decreased cloud formation. If the Svensmarkers are to have any credibility going forward, this is their moment in the sun. Where I sit, its still pretty cloudy.
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  22. Everyone use cloud formation as proof of connection between GCR and climate, whatever direction it is, as it is the one and only possible cause. What if there is another? In the lower region of the GCR energy spectrum, 10MeV-1GeV, where the flux is high, it is still able to create air showers of relativistic speed. In this region solar activity modulate the flux of a factor 10 between minimum and maximum. What if the shock waves of the secondary particles (muons mostly), even if not strong enough to create air ions, but to "shake the extra heat" out of water and CO2 molecules, in order to increase the loss of stored greenhouse energy. That is, making the night radiation into space to vary between solar minimum and maximum. Or put another way, solar activity modulate the degree of greenhouse effect. Is this a totally wild idea?
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  23. 122 - ibir The 'shock waves' of relativistic particles is called Cherenkov radiation. It's quite easy, given the momentum of the particles, the refractive indecies etc. to work out the radiation spectrum... normally it's towards the ultraviolet and higher - you can then look at the absorption spectrum of CO2 etc. to calculate it's impact. Using e-m radiation to 'shake out' heat sounds interesting but I've no idea what that means. Stimulated emission? Something a bit fancier? Is this a totally wild idea? you'd have to do the maths to find out.
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  24. A recent senior thesis at MIT (not as good as a PhD thesis, but still no slouch), Quintero 2010 calculates the Cerenkov threshold energy for muons in air as 4.4 GeV; this depends on angle and index of refraction (n). It would thus be far more likely to see the Cerenkov effect as these particles pass through water (higher n).
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  25. 123 - les As a non-physicist, the maths is far beyond my skill, and, I wasn't thinking so much about Cherenkov radiation, just that when the charged muons are able to strip electrons from atoms/molecules, when flying by in relativistic speed, then they might much more be able to stimulate release of a temporarily stored photons (~10um), earlier then by chance anyway.
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  26. 125 - ibir Physicist or not, you're speculating about physics and need a certain amount of background. First you said "not strong enough to create 'air ions'" now "able to strip electrons"... Molecules with stripped electrons are ions. etc. naybe there should be a post with more fundimental phulysucs concepts .. But, really, a good go at wiki is a mInimum and you could try to point a physics mechanisms outlined there.
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  27. ibir#125: "they might much more be able to stimulate release of a temporarily stored photons (~10um)," Muon-induced ionization does not result in photon emission: mu + atom -> mu + ion + electron (no photons here). Infrared wavelength photons (10um) are absorbed/emitted by molecular vibration. The molecules involved are GHGs: H2O, CO2, etc. Muons may interact with atomic nuclei, but not with such molecules. So that is not a valid mechanism either. Look at it this way: if muons interacted with greenhouse gas molecules, their flux rate at sea level would be a GHG detector. It isn't.
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