Comments 1 to 27:

1. Bodo at 05:51 AM on 27 September, 2010
   Thank you, very informative and well written! There is one paper you could add, Rohs et al. 2010: A correlation study of high-altitude and midaltitude clouds and galactic cosmic rays by MIPAS-Envisat, http://www.agu.org/pubs/crossref/2010/2009JD012608.shtml They also examined forbush events and they found a small effect (while Calogovic et al. 2010 found no effect), but in the wrong direction!
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2. SoundOff at 05:53 AM on 27 September, 2010
   Good article Dana. One variation I’ve seen on this skeptic argument is that the length of the solar cycle (10.66 years on average) is more meaningful to cloud effects and/or temperatures than the amplitude of the cycle. Cycle 23 was a long one, ~12.5 years long, which means we should experience cooling over the 8 years following the 2002 peak. Of course they predict the next few cycles to be long ones too. I’m sure it’s no more than astrology but some clear evidence against this line of reasoning would be nice to have. A snippet of this idea is presented below with a link to all the gory detail. “The cycle length of cycle 22 which peaked in 1990 was 9.8 years. Landscheidt has suggested a lag of up to 8 years between solar peaks or troughs and temperatures, which would mean a peak warmth from 1995 to 1998. Global temperatures appear to have peaked in 1998. The current longer quieter cycle 23 may be behind the cooling in the last 7+ years.” – Ultralong Solar Cycle 23 and Possible Consequences May 26, 2008
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3. SoundOff at 05:59 AM on 27 September, 2010
   Or is a peak in warming 8 years following the 2002 peak? Their line of reasoning seems inconsistent.
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4. gallopingcamel at 07:29 AM on 27 September, 2010
   For once I have to agree with your conclusions. Galactic Cosmic Rays do appear to have an effect on cloud formation but it is not the dominant effect that Svensmark, Friis-Christensen and Shariv might wish for. However, the correlation between "Cosmic Ray Intensity" and "Sunspot Number" shown in your Figure 2 is striking. Likewise, Figure 4 that shows the imperfect correlation between "Cloud Formation" and "Cosmic Ray" variation. Personally, I don't buy the idea that GCRs have a major impact on climate but these are interesting correlations that need to be better understood.
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5. muoncounter at 08:44 AM on 27 September, 2010
   The GCR-cloud seeding link isn't so obvious: A few comments on the CERN CLOUD experiment here and here. Note two key NASA reports during the last solar minimum: Cosmic rays hit space age high Solar wind loses power The Pierre Auger GCR observatory has as yet unpublished indications of increased frequency of GCR events as the solar magnetic field wound down. All point towards ideal conditions for GCR-induced cloud formation and the cooling that is supposed to accompany it. Annual reports from the US of that so-called cooling: Based on data from January through December [2009], the average annual temperature for the contiguous U.S. was 53.1 degrees F (11.7 degrees C), which is 0.3 degrees F (0.2 degrees C) above the 20th Century average Based on data through the end of 2008, the contiguous U.S. experienced a nationally averaged temperature that was the coolest in more than ten years. The average temperature of 53.0°F (11.7°C) was 0.2°F (0.1°C) above the 20th century (1901-2000) mean. Conclusion? A definite maybe. This particular piece of science isn't settled.
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6. dana1981 at 08:49 AM on 27 September, 2010
   muoncounter - note that increased GCR flux would mean increased cloudcover, increased albedo, and global cooling, if the GCR theory were correct. Quite obviously we're not currently experiencing cooling, as 2010 has been a very hot year. I may update the article to include some of that information though. I recalled reading the NASA reports but couldn't remember where to find them. Thanks for that.
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7. muoncounter at 08:55 AM on 27 September, 2010
   #6: "Quite obviously we're not currently experiencing cooling" Yes, all the GCR cooling thus far has definitely been underwhelming.
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8. Joe Blog at 09:16 AM on 27 September, 2010
   Dana says "In addition to these multiple lines of empirical evidence which contradict the GCR warming theory, the galactic cosmic ray theory cannot easily explain a number of observed fingerprints of the increased greenhouse effect, such as the cooling of the upper atmosphere" Unrelated to the whole cosmic ray hypothesis, the types of radiation are more variable through the solar cycle than TSI, most notably UV. This in itself could most certainly cause upper atmosphere cooling. Through its effect on ozone production and obviously heating o the stratosphere, is primarily through uv absorption by O3. This in itself could most certainly have an effect on the jet stream, and the pressure systems in the troposphere.... there is a lot to be learnt as far as solar effects on climate go. http://www.giss.nasa.gov/research/briefs/rind_03/
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9. Philippe Chantreau at 13:55 PM on 27 September, 2010
   Dana, thanks for mentioning in your review that the main problem about the GCR hypothesis is particle growth. That physical part of it has no solution to date. I do not believe that any significant effect on cloud nucleation exists from GCR at all. No correlation has been demonstrated to the necessary level of confidence.
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10. Glenn Tamblyn at 22:48 PM on 27 September, 2010
    Dana Good Post Personal view is that Svensmark has at best possibly identified a small contributing factor to the residual climate varibility left after allowing for AGW, El Nino's etc. Useful line of marginal investigation (and he may be right at that level) but don't stop the presses. And this post supports that. However one area I would pick up on, just to be pedantic.... Links to Chernobyl. The theory of GCR influences is specific about the energies of the radiation involved, height in the atmpsphere etc. The suggestion that Chernobyl might be expected to provide supporting evidence is drawing a long bow.... The difference between Alpha, Beta & Gamma radiation etc, and the energies envolved. I personally wouldn't expect Chernobyl to provide any evidence pro or con.
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11. Glenn Tamblyn at 23:02 PM on 27 September, 2010
    Phillipe Chantreau @9 Good Comment The problems with Svensmark's theory seem to be: 1. Particle growth. 2. Competition with other sources of CCN's that allow his Cosmogenic sourced CCN's to predominate and thus drive the impact. 3. Questions re the total impact of CCN's on the net positive or negative impact of the radiative forcing impacts of Cloud changes. 4. No evidence of long term trend in Cosmic ray fluxes to support long term trend in climate influences. So.... A minor contributing factor to residual climate variability.. Yeh, Maybe. A major driver of climate change. Show me the data. Otherwise he's dreaming. And his act of climbing into bed with the more radical climnate denialist cause has damaged his case. He may well have identified a modest contributor to residual climate variability. But by overselling his case and getting into bed with the whacko's, he has done himself a dis-service. Sad really.
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12. muoncounter at 02:57 AM on 28 September, 2010
    #10:"I personally wouldn't expect Chernobyl to provide any evidence pro or con." I don't see how low energy alpha or beta radiation could go far enough to ionize any part of the atmosphere. To consider gamma radiation as a factor, you could look at Gamma ray bursts. In March 2003, a large GRB was detected: The burst poured out a thousand trillion, trillion times the gamma rays seen in a solar flare. When measured more than one hour after the burst, the afterglow was still about as bright as a 12th magnitude star. But its not clear at all if this radiation seeds clouds.
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13. dana1981 at 04:21 AM on 28 September, 2010
    I took the Chernobyl discussion straight out of Sloan and Wolfendale (linked in the article). "We estimate that the increase in ionization from this [Chernobyl] radioactivity relative to that produced by CR is a factor of ~15 in the immediate vicinity of Chernobyl (50-52.5◦ N, 30-32.5◦ E) and a factor ~3 in the fallout region..."
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14. EliRabett at 13:33 PM on 28 September, 2010
    The basic problem is that cosmic ray seeded CCNs are not the only aerosols that can seed clouds.
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15. Argus at 18:24 PM on 28 September, 2010
    "Fortunately we have empirical observations against which we can test these requirements." Somehow I stopped to think about the connotation of this sentence from the prolog. Question: Why is the word 'fortunately' appropriate in this context? (a) Because it is such a joy to be able to 'debunk' all skeptic arguments? (b) Because it would be terrible if somebody holding opinions other than ours would ever be right, plus it would be so embarassing if main stream climate scientists were ever wrong?? (c) Because if our climate was governed by outer space, there would be nothing we could do about it - now, all we have to do is stop burning coal and oil? (d) Because of other reason (please specify!) (Check one)
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16. adelady at 18:30 PM on 28 September, 2010
    No Argus. It's fortunate that we live in the times that we do with all the advantages of scientific instruments unimaginable to earlier generations. It's worth reminding ourselves of that from time to time. It's not just dentistry and antibiotics that make this a good time for us. There's a whole infrastructure of scientific endeavour which we don't bother to look at most of the time. When we need it, it's there.
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17. VeryTallGuy at 20:54 PM on 28 September, 2010
    Argus (d) Fortunately rather than being ignorant and subject to argument by arbitrary assertion, we can use facts to check our understanding of the world.
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18. dana1981 at 04:35 AM on 29 September, 2010
    Argus, it's *always* fortunate when there is empirical data against which we can test *any* theory. If his theory were correct, Svensmark would be fortunate that the data exists to confirm it.
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19. Glenn Tamblyn at 10:06 AM on 29 September, 2010
    Interesting article in this weeks New Scientist about possible links between the Solar Cycle and climate. The mention Svensmarks theory and that it has issues, but also mention another mechanism where GCR's may have more impact. Rather than creating CCN's to seed cloud formation, they may contribute to explaining the fact that clouds are often charged on their top and bottom surfaces as GCR's may ionise existing droplets. Speculation is that this could impact on the lifetime of a cloud, precipitation rates from a cloud etc. Certainly a more plausible then Svensmarks more convoluted mechanism. But these may not be the only impacts of Solar variability. Possibly variations in solar wind and magnetic field strengths could impact on the rate of deposition of cometary and meteoritic dust from space, another source of CCN's. Preliminary evidence suggests that although TSI only varies by about +/- 0.1% over a solar cycle, the Ultraviolet component of this may vary by as much as 1-2%. Ultraviolet is preferentially absorded in the stratosphere by ozone, but in addition UV is also part of the cycle vy which Ozone is actually created and destroyed, as well as the processes by which CFC's are destroyed, all of which can impact on climate. Also the stratosphere is where methane is converted to CO2 & Water so changes in the chemistry up there due to Solar cycle influences could impact on levels of Methane. Interestingly, Methane levels in the atmosphere plateaued for much of the 2000's, only to resume rising towards the end of the decade, roughly in line with the 'It hasn't warmed since 1998' period. Coincidence? And there may well be other mechanisms yet to be found by which different components of the solar system that vary with the solar cycle may have climate impacts - UV, Solar wind, Magnetic Field strengths, Simply correlating just GCR's to Atmospheric Temperature variability alone and implying a single major forcing here is stretching too long a bow. I suspect we will find a range of different mechanisms, caused by different phenomena associated with the solar cycle that each make modest contributions to climate variability. This doesn't in any way detract from the central theories about AGW that are based on solid radiative physics. Rather these would be simply additional secondary mechanisms that contribute to climate variability. Put simply, AGW currently describes the physics driving underlying trends. A range of other factors, including but not limited too solar cycle factors probably explain shorter term climate variability that is overlaid on top of the underlying trend. And periods such as a decade of lesser warming is still just short term variability.. Never forget, to produce his graph correlating GCR's with temperature Svensmark not only removed the impacts of ENSO, Volcanoes etc to reveal the residual impact, but also he had to remove a .14 DeC PER DECADE TREND as well. AGW due to GH Gases AS WELL as Solar Cycles influences. Not INSTEAD OF.
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20. muoncounter at 10:27 AM on 29 September, 2010
    #19: "they may contribute to explaining the fact that clouds are often charged on their top and bottom surfaces as GCR's may ionise existing droplets." Glenn, Interesting post. Looking at the abstract of the GRL article cited in the New Scientist post you mention, I don't see any specific mention of GCRs as opposed to solar cosmic rays: Cloud edge droplet charging is expected from vertical flow of cosmic ray generated atmospheric ions in the global electric circuit. Its long been known that solar cosmic rays (mostly muons - my personal favorite), are ionizing. The origin of cosmic ray research was an effort to explain why charged, shielded electroscopes spontaneously lost their charge. Solar cosmic rays are vastly more abundant than GCRs and thus would be more likely candidates for 'cloud edge droplet charging.'
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21. Glenn Tamblyn at 15:18 PM on 29 September, 2010
    muoncounter @20 I wasn't aware of the distinction between the two sources of Cosmic Rays. Do you know whether the underlying fluxes of SCR's from the Sun are constant; as distinct from the levels reaching the Earth which are influenced by Solar cycle influenced shielding of the planet? Or do the raw fluxes vary with the Solar cycle?
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22. muoncounter at 23:49 PM on 29 September, 2010
    #21: Solar cosmic rays are produced by solar wind ions (protons mainly) striking gas nuclei in the upper atmosphere. The flux to the upper atmosphere is thus a product of solar activity (CMEs and flares), observed for several years now by NASA's ACE satellite. The flux at the surface, measured for many years by an international network of neutron monitors and more recently by a network of 'muon counters', varies on a scale of hours, days, months for different types of solar events. These are typically low energy particles, moving at relativistic speeds. The earth's magnetic field (as distinct from the solar or interplanetary magnetic field) is a strong modulator of solar cosmic ray flux. That's why auroral displays (the interaction of charged particles in the earth's magnetic field) are mainly visible in the high latitudes. GCR flux, even in times of the lowest solar magnetic field intensity, is much smaller than solar cosmic ray flux. The key point about GCRs is that they are much higher energy than solar cosmic ray particles.
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23. HumanityRules at 01:51 AM on 17 November, 2010
    On the issue of GCR Cloud Seeding You seem to have completely ignored the body of work by Harrison and others who have made in situ cloud observations which "are consistent with enhanced production of large cloud droplets from charging at layer cloud edges." There's an example of their work below but also many more from what I can see in literature searches. Harrison and Maarten 2009
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24. muoncounter at 04:51 AM on 17 November, 2010
    #23: The Harrison and Ambaum 2009 paper you cite is about earth's electric field; it has nothing to do with this topic. The words 'cosmic ray' appear in the abstract, keywords and a non-specific reference to a 1989 paper. The statement in the abstract ... arising from the combination of distant thunderstorms, Earth’s conducting surface, a charged ionosphere and cosmic ray ionization is utterly inconclusive. Neither 'GCR' or 'galactic' appears at all.
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25. Tom Curtis at 17:36 PM on 25 February, 2011
    Responding to Muoncounter: ""may be a connection between low solar activity and lack of major volcanoes, ... may also be an impact of galactic cosmic rays, ... on cloud albedo." They're way off topic, but those are new ones on me. If you can find an appropriate thread, care to explain?" This is just a speculative thought of mine about Svenmark's hypothesis. My first thought when I heard Svenmark's hypothesis is exactly described by El @14 above. There is an abundance of Cloud Condensation Nuclei, particularly over ocean (salt from sea spray), desert (dust) and forest (aramotic compounds released from leaves). Adding one more source of CCN is therefore unlikely to increase cloud cover. However, adding additional CCN is known to reduce the average droplet size within clouds. This can be seen most easily in ship tracks: It is also a known effect of industrial polution, with clouds downwind of cities typically having smaller than usual droplet size. (This does not get much discussion when deniers discuss the Urban Heat Island effect, and surface station placement, for reasons that will become obvious.) Decreasing cloud droplet size has two effects. It decreases the probability of rain, and it increases the albedo of the cloud. The former may result in longer lasting clouds, but if humidity drops, it is unlikely to compensate for the faster evaporation due to the increased surface area per unit volume from smaller droplet size. However, the increased albedo is real, detectable, and will have a cooling effect. So, assuming that Svenmaark is right in claiming that GCMs form CCN, and he has at least mounted a plausible case, then increased GCMs will increase cloud albedo by a small amount. It is obviously not a large amount because, if it were, the effect would be very obvious in the temperature record as a strong correlation between temperature and Sun Spot Number. But it may explain the small correlation seen between temperature and SSN surface temperatures, and some of the correlation between deep solar minima and cool temperatures which far excede the ability of TSI changes to explain.
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26. muoncounter at 06:41 AM on 26 February, 2011
    Tom, "increased GCMs will increase cloud albedo by a small amount. It is obviously not a large amount because, if it were, the effect would be very obvious in the temperature record " Thanks. But that albedo increase may well be below any reliably detectable threshold. It would seem to be a second-order mechanism to the whole Svensmark idea, which has thus far eluded reliable detection on its own. It was really the low solar-lack of volcano activity link that made me wonder what I had missed way back when in my 'shake and bake' class. Editors: an unclosed italics tag seems to have infected this thread, immediately after Fig 4.
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    Moderator Response: [Daniel Bailey] I took a look at it; the error is in the html editing window. It's like The Matrix, raw code. Gonna take a bigger boat than I have to fix...
27. muoncounter at 14:01 PM on 26 February, 2011
    DB, (or should I call you Spoon Boy?) Do not try to bend the spoon fix the italics tag — that's impossible. Instead, only try to realize the truth: there is no spoon italics tag.
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    Moderator Response: [DB] Yes, Obi-Wan; this Padawan realized his error, adapted, improvised and overcame. Move along, go about your business now.

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