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The CERN/CLOUD results are surprisingly interesting…

Filed under: — gavin @ 24 August 2011

The long-awaited first paper from the CERN/CLOUD project has just been published in Nature. The paper, by Kirkby et al, describes changes in aerosol nucleation as a function of increasing sulphates, ammonia and ionisation in the CERN-based ‘CLOUD’ chamber. Perhaps surprisingly, the key innovation in this experimental set up is not the presence of the controllable ionisation source (from the Proton Synchrotron accelerator), but rather the state-of-the-art instrumentation of the chamber that has allowed them to see in unprecedented detail what is going on in the aerosol nucleation process (this is according to a couple of aerosol people I’ve spoken about this with).

This paper is actually remarkably free of the over-the-top spin that has accompanied previous papers, and that bodes very well for making actual scientific progress on this topic.

The paper first confirms some results that are well known: aerosol nucleation increases enormously when you add H2SO4 into the air (the biggest contributor to human aerosol impacts via the oxidation of our emissions of SO2), it increases further when you add ammonia (NH3), and it increases even more when you increase ionisation levels from neutral, to ambient ground levels, and to upper atmospheric levels (as long as you are below what is called the ‘ion-pair’ limit). However, the most intriguing result is that despite going to a lot of trouble to make sure the chamber was ultra-free of contaminants, the researchers found that within most of the aerosols that formed, there were traces of organic nitrogen compounds that must have been present in almost undetectably low concentrations. The other intriguing finding is that aerosol nucleation rates in the chamber don’t match (by a an order of magnitude or more) actual formation rates seen in real world near-surface atmospheric layers at realistic temperatures (only in unrealistically cold conditions do rates come close). The authors speculate (quite convincingly) that this is precisely because they didn’t have enough volatile organic compounds (which are ubiquitous in the real world) to help get the nucleation started. This result will surely inspire some of their next experiments. All-in-all this is a treasure trove of results (and potential future results) for people tasked with trying to model or understand aerosol processes in the atmosphere.

Annotated Fig 5 from Kirkby et al
Figure 1: Annotated version of fig 5 in Kirkby et al. Small dots are in situ observations, lines are other lab data. Colours for the CLOUD results are coded with respect to temperature. Going from open to filled symbols denote increasing NH3. All results are for ambient CR ionisation (changes in CR only make a difference below the ion-pair limit).

However, aerosol nucleation experiments are not usually front page news, and the likely high public profile of this paper is only loosely related to the science that is actually being done. Rather, the excitement is based on the expectation that this work will provide some insight into the proposed cosmic ray/cloud/climate link that Svensmark (for instance) has claimed is the dominant driver of climate change (though note he is not an author on this paper, despite an earlier affiliation with the project). Indeed, the first justification for the CLOUD experiment was that: “The basic purpose of the CLOUD detector … is to confirm, or otherwise, a direct link between cosmic rays and cloud formation by measuring droplet formation in a controlled test-beam environment”. It is eminently predictable that the published results will be wildly misconstrued by the contrarian blogosphere as actually proving this link. However, that would be quite wrong.

We were clear in the 2006 post that establishing a significant GCR/cloud/climate link would require the following steps (given that we have known that ionisation plays a role in nucleation for decades). One would need to demonstrate:

  1. … that increased nucleation gives rise to increased numbers of (much larger) cloud condensation nuclei (CCN)
  2. … and that even in the presence of other CCN, ionisation changes can make a noticeable difference to total CCN
  3. … and even if there were more CCN, you would need to show that this actually changed cloud properties significantly,
  4. … and that given that change in cloud properties, you would need to show that it had a significant effect on radiative forcing.

Of course, 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).


Figure 2: Normalised changes in cosmic rays since 1953. There has not been a significant downward trend. The exceptional solar minimum in 2008-2010 stands out a little.

The CLOUD results are not in any position to address any of these points, and anybody jumping to the conclusions that they have all been settled will be going way out on a limb. Indeed, there is a lot of evidence that (particularly) point 2 will not be satisfied (see for instance, Pierce and Adams (2009), and a new paper by Snow-Kropla et al).

So what changes did they show as a function of the CR activity? In going from neutral (shielded) conditions to ambient CR levels typical of the lower atmosphere, the ionisation changed by a factor of 2 to 10 (depending on the temperature – colder conditions are more sensitive). However this is a much bigger change (by an order of magnitude or more) than the percentage change in CR activity over a solar cycle (i.e. ~10-20%). A rough calculation (by way of Jeff Pierce) that takes into account the square root dependence of ion concentrations on GCRs and the neutral nucleation in the CLOUD results, suggests that for average conditions the solar modulation of GCR would impact nucleation by about 1% – rising to perhaps 12% for the biggest changes in GCR seen in figure 2 at very cold temperatures. Thus the nucleation change as a result of real world GCR modulation is going to be much smaller than seen in these experiments, and much less important than the amount of pollutants.

In summary, this is a great example of doing science and making progress, even if it isn’t what they first thought they’d find.

220 Responses to “The CERN/CLOUD results are surprisingly interesting…”

  1. 1
    SteveF says:

    I would be interested in thoughts on this new research from the CLOUD project. A write up at Nature entitled “Cloud formation may be linked to cosmic rays”

    the paper:


    [Response: You've got it. - gavin]

  2. 2
    SteveF says:

    A first rate service! I will come here again!

  3. 3
    arch stanton says:

    I don’t see Svensmark listed as an author (confirming the RC in-line comment from a few weeks ago). One of his papers is listed as a reference in the abstract for background information.

  4. 4
    Pete Dunkelberg says:

    Just saying Kirby et al. doesn’t do it justice:

    Nature | Letter

    * Previous abstract
    * Next abstract

    Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation

    * Jasper Kirkby,1
    * Joachim Curtius,2
    * João Almeida,2, 3
    * Eimear Dunne,4
    * Jonathan Duplissy,1, 5, 6
    * Sebastian Ehrhart,2
    * Alessandro Franchin,5
    * Stéphanie Gagné,5, 6
    * Luisa Ickes,2
    * Andreas Kürten,2
    * Agnieszka Kupc,7
    * Axel Metzger,8
    * Francesco Riccobono,9
    * Linda Rondo,2
    * Siegfried Schobesberger,5
    * Georgios Tsagkogeorgas,10
    * Daniela Wimmer,2
    * Antonio Amorim,3
    * Federico Bianchi,9, 11
    * Martin Breitenlechner,8
    * André David,1
    * Josef Dommen,9
    * Andrew Downard,12
    * Mikael Ehn,5
    * Richard C. Flagan,12
    * Stefan Haider,1
    * Armin Hansel,8
    * Daniel Hauser,8
    * Werner Jud,8
    * Heikki Junninen,5
    * Fabian Kreissl,2
    * Alexander Kvashin,13
    * Ari Laaksonen,14
    * Katrianne Lehtipalo,5
    * Jorge Lima,3
    * Edward R. Lovejoy,15
    * Vladimir Makhmutov,13
    * Serge Mathot,1
    * Jyri Mikkilä,5
    * Pierre Minginette,1
    * Sandra Mogo,3
    * Tuomo Nieminen,5
    * Antti Onnela,1
    * Paulo Pereira,3
    * Tuukka Petäjä,5
    * Ralf Schnitzhofer,8
    * John H. Seinfeld,12
    * Mikko Sipilä,5, 6
    * Yuri Stozhkov,13
    * Frank Stratmann,10
    * Antonio Tomé,3
    * Joonas Vanhanen,5
    * Yrjo Viisanen,16
    * Aron Vrtala,7
    * Paul E. Wagner,7
    * Hansueli Walther,9
    * Ernest Weingartner,9
    * Heike Wex,10
    * Paul M. Winkler,7
    * Kenneth S. Carslaw,4
    * Douglas R. Worsnop,5, 17
    * Urs Baltensperger9
    * & Markku Kulmala5
    * Show fewer authors

    There must be a joke that starts “How many physicists does it take to write a paper?”


    Atmospheric aerosols exert an important influence on climate1 through their effects on stratiform cloud albedo and lifetime2 and the invigoration of convective storms3. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours4, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small5, 6. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia7. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100–1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H2SO4–H2O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.


    What is the boundary layer of which they speak?

  5. 5
    vboring says:

    It seems like steps 1-3 are pretty well demonstrated by Forbush Decrease studies that show a short term rapid changes in solar activity producing an impact on cloud cover. Are you suggesting that the sun is impacting cloud cover through a mechanism other than cosmic rays?

    sorry if this is a repeat the captcha system is a pain.

  6. 6
    Chris Colose says:


    The boundary layer is the lower part of the troposphere, roughly where the flow is still influenced by Earth´s surface (friction)

  7. 7
    Jeroen says:

    Wow… Spin spin spin…

    [Response: You should probably learn the difference between context and spin. Here's a link to help you distinguish. I count 3 lies in the title and first paragraph alone. - gavin]

  8. 8
    Jimmy James says:

    I would have thought Rasmus would be the one to respond to this given his previous posts on the subject. I wonder what he thinks of the results.

  9. 9
    Scottie says:


    You say:

    “The other intriguing finding is that aerosol nucleation rates in the chamber don’t match (by a an order of magnitude or more) actual formation rates seen in real world near-surface atmospheric layers at realistic temperatures (only in unrealistically cold conditions do rates come close).

    I understand that the CLOUD experiment considered temperatures down to –25C which is equivalent to only about 20000ft or 6000 metres altitude.

    Given that clouds exist at all altitudes up to the tropopause, (and even above in some circumstances) where the temperature is typically –56C and below, are you suggesting that only low, near-surface clouds can affect albedo? Surely high altitude clouds cannot be discounted?

    [Response: The comparison being made in the figure was to boundary layer clouds - and so -25 C is unrealistic. It might well be that mid-troposphere comparisons would be better - but you would have different H2SO4, specific humidity and pressure so it is not obvious that what they have now is relevant to real world mid-trop values. Your larger point is well taken - there is no magic rule that says that this mechanism can only work for low clouds - one might expect impacts all through the atmosphere as a function of all these inputs (GCR (higher aloft and near the poles), H2SO4 higher in polluted regions near the surface, temperature etc.). This is precisely the reason why one cannot automatically assume that the net radiative forcing would be negative (remember higher clouds have a significant greenhouse impact). - gavin]

  10. 10
    Jeffrey Park says:

    What is the boundary layer of which they speak?

    The boundary layer that you and I breathe in while we walk around, I believe.

  11. 11
    R. Gates says:

    Just a few broad questions related to the potential GCR/Cloud relationship in context of overall longer-term climate modulation:

    1) Does this provide yet one more potential explanation of the causes of the Little Ice Age? Though the Maunder Minimum has long been suspected as related at least in part to the cooling seen during this period, the lower TSI in and of itself, was never enough to provide such a cooling, so would a tighter connection between the slightly lower TSI of the Maunder (and hence higher GCR) provide a bit more of a mechanism for the period?

    [Response: Undeteriminable at this stage because we don't actually know the impact on real clouds, or what the net radiative effect might be. It could even be positive (since colder areas are more sensitive to CR, and high clouds have a net warming effect). But see too the last post - MM TSI is also uncertain so whether it is or it is not sufficient is unclear. - gavin]

    2) Related to question 1), what implications are there for judging the relative strength of the forcing from periods of higher GCR’s versus higher CO2? This question may indeed come back to aerosols, as perhaps a combination of higher volcanic activity PLUS increased GCR’s, is far more potent in providing cooling. Meaning that, each period of low solar activity, such as the Maunder, must be looked at in the overall context of other factors, with aerosols playing a pivotal role in determining the potency of effect. I think about this question more on the very long term scale as well, as the solar system in traveling around the galactic center, may pass through dustier areas or periods of higher GCR’s, and the combination, when occurring at the same time, could provide extra aerosol boost to making clouds.

    [Response: None as yet because you don't know the sign or the magnitude of the radiative forcing, let alone how much GCR shielding exists in the rest of the galaxy. This just ends up being unconstrained speculation. - gavin]

  12. 12
    Meow says:

    On a related topic, Palle et al 2004 explored changes in earthshine-determined albedo, concluding that albedo fell by ~0.02 from 1985 to 1997, then rose by almost the same amount until 2003 when their data series ended. How useful is this technique?

    [Response: Compared to the ERBE/CERES data it doesn't appear to be accurate enough to be useful. - gavin]

  13. 13
    Jeff Pierce says:

    vboring: I believe that the Svensmark FD paper does show a strong connection between cosmic rays and clouds (and some aerosol properties too) that is hard to have happened by chance. I had to repeat some of the analysis myself to believe it (having already published a paper that found that the CCN should not be greatly changed by cosmic rays).

    However, we don’t know what physical pathway connects cosmic rays to clouds. The aerosol nucleation/CCN pathway is the one that CLOUD is currently testing, the one I have explored and the one that has generally gotten the most attention. However, there are other ways cosmic rays and clouds might be linked, although we know even less about them. This paper ( is a nice overview.

    Unfortunately, until we fully understand these physical links, it is difficult to predict how cosmic rays may have changed climate. And as Gavin says above, there really hasn’t been any trend in cosmic rays in the past 50 years.

  14. 14
    Hank Roberts says:

    “… observed correlation between cosmic ray intensity and Earth’s average cloud cover over the course of one solar cycle….” (Carslaw et al. 2002)

    What, if any, intervening variables have been thought about? Have any been eliminated? (Blue-skying, I wonder if plankton DMSO production varies (the quantity, or the dominant species, or ???) with the solar cycle, perhaps correlated with changes in the amount of UV getting through to the ocean surface.)

  15. 15
    Eli Rabett says:

    A regional atmospheric modeler Eli knows thinks that the nucleation process needs NOx as well as H2SO4

  16. 16
    JimA says:

    Gavin why is your Cosmic Ray graph above significantly different from the Moscow Neutron Monitor which clearly supports a downward trend.

    [Response: Your moscow data only goes to 2006 - more up-to-date data here. I will plot it on the same graph and link it here. There are minor differences in the neutron monitors that depend on latitude, pressure corrections, sensitivity, but they are all very highly correlated. There is no significant long term trend. - gavin]

  17. 17
    Hank Roberts says:

    DMS measurements and variation:

    Relating Atmospheric and Oceanic DMS Levels to Particle Nucleation Events in the Canadian Arctic

    Oceanic Dimethyl Sulfide Emission and New Particle Formation

    Plenty more there. I know this must be well discussed somewhere (pointer welcomed). It’s just the one mechanism I happen to have heard about, that seems likely to be able to multiply a little variation in solar influence greatly over a few years, given how fast plankton populations can boom.

    Makes more sense to me than pure physics explanations for changing cloudiness. But, then, I was raised by and among biologists ….

  18. 18
    Edward Greisch says:

    Gavin: I don’t understand what is unrealistic about 25 below C, unless you live down south. I have been outside in central Iowa when the straight temperature was 40 below. -25C = +13F. 25 C below is no big deal. Actually, +13 degrees F is fairly warm. The sky can be gray at that temperature. In western New York state, 40 below is too cold for snow, but that doesn’t mean the ceiling is unlimited.

    Your CV says you are from Oxford, England and New York City. NYC is south of my home town, but not that far.

    13 Jeff Pierce: Why don’t I see cosmic ray tracks on foggy days? Did the charged pion beam make a cloud that looked like a beam?

    “All measurements were made at 38% relative hum”idity. Why were the experiments done at such a low relative humidity?

    Killer sentence: “Given the uncertainties in these models, many scientists consider there is no convincing evidence at present to demonstrate that a greenhouse warming of the planet is in progress,” The denialists quoted it at:

  19. 19
    CM says:

    Hank #14, 17,

    I’ve wondered about solar/DMS, too, but thought it was just me. I’ve googled a bit to no effect.

  20. 20
    Theo Kurtén says:

    Eli: the nucleation process in itself probably doesn’t involve or need NOx, but growth to larger (e.g. climate-relevant) sizes almost always needs condensable organic vapors, and their formation usually involves NOx one way or the other. And of course NOx affects oxidant concentrations, which also drives the production of H2SO4 – but this is still different from actually directly participating in the process. (From a regional modeling viewpoint, the difference between nucleation and subsequent growth might not be that big, but it certainly is for us nucleation modellers!)
    Hank: in addition to DMS, algae also likely emit nitrogen-containing bases (like amines) which are also important for particle formation. Continuing on your blue-sky hypothesis, these emissions could conceivably also be dependent on UV.

  21. 21
    AIC says:


    In your response to #16, the second link “I will plot it on the same graph and link it here.” does not work. Error 404

    [Response: Fixed. thanks. - gavin]

  22. 22
    Tea Partier says:

    “…There is no significant long term trend…”

    (in the neutron count)

    True, but there is downward trend in the period 1966 to 1996, when a lot of warming took place. What happened after is a climb in the neutron count, which might explain the lack of gain in ocean heat after 2003.

  23. 23
    CM says:

    vboring #5, Jeff Pierce #13, re: Forbush decreases affecting clouds,

    Then on the other hand, Kristjánsson et al. (2008) had looked pretty carefully for an effect of FD events on clouds and didn’t find much of anything significant. Some questions about Svensmark’s 2009 paper were raised here at the time. The jury’s still out, perhaps?

  24. 24
    Jeff Pierce says:

    18 Edward Greisch: You cannot visibly see the effects of cosmic rays with your eyes. Clouds are not instantly formed when cosmic rays form ions in the atmosphere, which is a good thing since cosmic rays create more than 10 ion in every cubic centimeter of air each second (we’d be engulfed in thick clouds all of the time!). The ions from cosmic rays aid in forming aerosol particles that are too small too see. These particles may eventually grow (over the course of several days) by condensation of sulfuric acid and organic vapors to be large enough for a cloud droplet to form on (even then a cloud droplet will only form when the air becomes saturated with water vapor, and this needs to happen independently of these other processes).

    Thus, the pion beam did not make a cloud that looked like a beam. In fact, no clouds were formed during these experiments at all (as you point out, the RH was ~38% and you need to reach >100% RH to form a cloud). These cloud experiments only tested the very first step of this cosmic-ray/aerosol/cloud hypothesis (the aerosol nucleation step). There are plans in the future cloud experiments to test the other steps (and other, entirely different, cosmic-ray/cloud connections).

    Hope this helps!

  25. 25
    cRR Kampen says:

    Tea Partier says in #22 “True, but there is downward trend in the period 1966 to 1996″ and a strong upward trend since, peaking in 2010 which is one of the warmest years in the temperature record, while the first decennium of this century is by far the warmest in the record. Please explain these cherries.

  26. 26
    Robin Levett says:

    @Tea Partier #22:

    True, but there is downward trend in the period 1966 to 1996, when a lot of warming took place.

    What’s the magnitude and significance of that trend; how have you calculated both?

    Is there a significant trend between 1986 and 1996?

  27. 27
    Lotharsson says:

    -25C = +13F

    Not quite: -25C = -13F.

  28. 28
    Dikran Marsupial says:

    Pete Dunkelberg writes: There must be a joke that starts “How many physicists does it take to write a paper?”

    Perhaps but the parody has been in print for a fair while ;o)

    August et al., “The effects of Peanut Butter on the Rotation of the Earth”, Annals of Improbable Research, 1993.

  29. 29
    Christo says:

    Another point that receives little attention is spatial variation in the secondary cosmic ray flux that reaches the lower atmosphere, as well as its composition. Upon reaching the upper atmosphere the primary cosmic rays (mostly protons) cause nuclear disintegrations, which in turn give rise to a shower of secondary cosmic rays, including the neutron flux that is typically used as a measure of CR strength and solar modulation.

    1) The neutron monitor data shown here are from Oulu, Northern Finland. At high latitudes solar modulation of cosmic rays is much stronger, at the equator you would be looking at <5% of variation. The reason for this is the shielding effect of the earth, which is strong at the equator, and practically absent at the poles. So the 10-20% you use in the calculations surely is an overestimate for the globe, in particular when weighed by the relatively small surface area of the high latitudes.

    2) The muon component of the secondary cosmic rays is often used to explain the ionizing effect of CRs. In the CLOUD study in Nature they use a pion beam (pions are also charged particles; pions have a short lifetime and typically decay to muons before reaching the lower atmosphere). However, the muons originate from high-energy primary cosmic rays, which are thought to be hardly modulated by solar activity, even at high latitudes. There is much less muon data available than neutron monitor data, which is probably the reason why the neutron data is always shown. But there is no reason to believe the muons are modulated in the exact same way that neutrons are.

    Many of these effects are nicely explained in Lifton et al 2005 ("Addressing solar modulation and long-term uncertainties in scaling
    secondary cosmic rays for in situ cosmogenic nuclide applications")

    To summarize: high latitude neutron monitor data do not represent the entire globe, and do not represent the muon flux that is held responsible for aerosol nucleation.
    Perhaps a 5th point to add to your list things that need be worked out before we can assess the influence of GCR on global climate!

  30. 30
    Yvan Dutil says:

    #22 Tea Partier If your interpretation was right, we would see large temperature swing over a solar cycle. However, this signal is much lower than the observed temperature change.

  31. 31
    vukcevic says:

    GCR count is most likely too low (unless there is some kind of ‘chain reaction’ within cloud formation process) to make any significant difference.
    But, if there is a GCR-climate link than the feedback may be a positive one (clouds also prevent heat loss at night, particularly at higher latitudes and the Arctic’s winter months).
    Some relevant facts:
    - The Earth’s magnetic field (gmf) is far stronger modulator of the GCRs then the heliospheric mf.
    - The Arctic’s gmf intensity moves in the opposite direction to the solar mf: (vukcevic discovery)
    - Since 1800 the global gmf lost about 10% of its strength, so the GCR count (and clouds) should have gone up strongly, and according to the Svensmark’s albedo hypothesis causing global cooling; but we had global warming since 1800, in line with the idea of a positive feedback induced by gamogenetically GCR modulation.
    - There is a good correlation between temperature movements and the gmf:

  32. 32
    gavin says:

    The CERN press briefing is quite good on what they say it all means. Particularly clear is their final conclusion: “However,

  33. 33
    tea partier says:

    #24 “…If your interpretation was right…”

    The 2 deepest “troughs” in the neutron count of 1982 and 1991 unfortunately were close to major volcanic eruptions (El Chichon and Pinatubo), so the results are muddied. Otherwise it is true that we should see warming pulses during the “troughs” in the neutron count on or after (approximately) 1958, 1969, 1981, 1990, and 2000. Is that true? I think if you extracted the ENSO “noise” from the signal it might be.

    [Response: You are clutching at straws. There would only be a minimal delay between GCR changes and cloud formation if this is a big effect. If you posit that the very small change from 1966 to 1996 is enough to cause a 1% (?) change in global clouds, then the solar cycle effects would be an order of magnitude larger. There is no evidence of this at all. Other factors also strongly mitigate against an effect this large - the ionisation from radon is dominant over much of the land surface - you would see that in the cloud data (you don't). The Laschamp excursion led to a dramatic increase in GCR around 40,000 years ago (seen clearly in the 10Be ice core data), but did not noticeably impact climate at all. This doesn't mean that there is no modulation of climate, just that it isn't the enormously dominant player people like Calder or Svensmark imagine. - gavin]

  34. 34
    Jeff Pierce says:

    CM #23. Yes, the case of the FD observations is definitely not closed. The difference between the Kristjánsson and Svensmark papers is likely the difference in the number of FDs used in their primary results (both papers agree that using the strongest cases strengthens observed trends and using more cases buries these trends); however, Kristjánsson chooses to highlight the results from 22 events, where Svensmark chooses to highlight the results from 5. Obviously the FD question would be easier to answer if we had more observed “strong” FD events.

    I was an opponent at Torston Bondo’s (Svensmark’s student) PhD defense. I wanted to know what I was getting myself into, so I re-analyzed much of the data in the Svensmark paper and tweaked some of their assumptions including some of the issues raised in the RC post (e.g. randomly removed 1 or 2 of the “big 5″ events, changed their criteria for their minimum daily AERONET measurements, not used any temporal smoothing) and the results do not change greatly. I definitely think the jury is still out, but I also think the Svensmark paper caries weight.

    This all being said, I still don’t have a clue as to why these cloud changes occur. The Pierce and Adams and Snow-Kropla et al. papers that Gavin mentioned in the article are modeling work that I or my group have done. They show that the changes in nucleation from cosmic rays (consistent with these CLOUD results) lead to insignificant changes in CCN (too small to greatly affect clouds). Luckily the CLOUD experiment people are planning on testing the nucleation-CCN connection, so we don’t need to rely on only modeling for these estimates, but it will be another year or so before we see these results, I think. If the CLOUD results on nucleation-CCN agree with my group’s modeling work, some entirely different processes must be going on if cosmic rays actually are affecting clouds (again see

  35. 35
    HR says:

    So if you are a lead author for the next IPCC report what do you do?

    Do you mention the climate/CGR link with one sentence or do you include it as a natural forcing with wide uncertainty limits or something else?

    I recognize this science is at an early stage but surely the IPCC has to deal with this even if it’s early. I guess I’m just looking for speculation/opinion on this.


  36. 36
    CM says:

    Jeff Pierce,

    Silly me, I didn’t connect your name with the papers. Thanks for an enlightening perspective on Svensmark’s Forbush paper.

  37. 37
    deconvoluter says:

    Fifth step.

    In addition to the four steps listed in the article, perhaps a fifth one should be added for “insensitivist fundamentalists” *.

    5…Demonstrate why the climate is effectively insensitive to the accumulation of greenhouse gases.

    * Exemplified in the UK by the medium term weather man, Pers Corbyn, the spinner linked after #5, and possibly some of the other contributors to Channel 4′s Swindle programme.

  38. 38
    Scott says:

    while there isn’t a downward or upward trend in the amount of CR, is there a trend in the amount of aerosols over the past 100 years or so?

    [Response: Yes. Mostly from coal, oil, agriculture, biomass burning. - gavin]

  39. 39
    Scott says:

    Also, does this hint at a possible solution to Global Warming? Could we just pump more aerosols into the atmosphere?

    [Response: No. Public health, acid rain implications make this a really bad idea. - gavin]

  40. 40
    deconvoluter says:

    Re: my previous comment.


    Suppose recent warming were to be attributed mainly to a reduction of low level cloud. Are there any finger prints associated with that?

    Wouldn’t that mean that days should have warmed more than nights?
    Wouldn’t that mean that the stratosphere would also have been warming?
    How would such a mechanism vary with latitude?

  41. 41
    tea partier says:

    #25 “…peaking in 2010 which is one of the warmest years in the temperature record,…”

    …straddled by what are likely to be (once 2011 is in) by 2 cold years (by recent standards). My point was that ocean heat gain is not there since 2003 and that coincides with an elevated neutron count since roughly the same time.

  42. 42
    tea partier says:

    #34 “…The difference between the Kristjánsson and Svensmark papers is likely the difference in the number of FDs…”

    Neither paper attempts to filter FD events for weather related masking of the effect (If my memory serves correct), but High/Low pressure systems in waxing/waning modes must have a large potential to obscure the GCR signal if it exists. That fact that a signal appears in the strongest FD events, irrespective of weather, is an indication the effect is significant.

  43. 43
    Bob from the UK says:

    With respect to figure 2, you say there has been no discernable trend. But that graph doesn’t plot the trend does it. (Hint) The trend depends on the not just the peak amplitude, but the troughs and the width of these peaks and troughs. The troughs actually show a downward trend to 1990 and recently there has been an upward trend. Of course we can’t really determine this by eyeballing the graph can we.

    Why don’t post the trend and not raw data?

  44. 44
    Hank Roberts says:

    > more aerosols
    DMS: The Climate Gas You’ve Never Heard Of
    Made by tiny plants in the ocean, dimethylsulfide helps make clouds in the sky
    “… the question becomes, can algae produce enough DMS to increase cloud cover and keep the planet’s temperature from rising ….”
    (good article, names many of those who are publishing in this area and provides links to their home pages and research articles)

  45. 45
    Edward Greisch says:

    24 Professor Pierce: Thanks

    27 Lotharsson: Thanks

    What happened to dust particles being the condensation nuclei? Aren’t there plenty of dust particles?

  46. 46
    Hank Roberts says:

    > climate/CGR link

    Don’t presume what you want to find out — whether there is a link.
    At most there are a variety of correlations and a variety of hypotheses, and they don’t consistently add up (yet), near as I can tell. That’s why I asked above about possible intervening variables or other factors that might also correlate with the observations and whether any have been investigated sufficiently to rule them out.

    Is this a fair summary to date?
    It says:
    “… while cosmic rays do seem to have some minor atmospheric effects, they do not seem to have anything to do with global warming, particularly over the past century. A.D. Erlykin, B.A. Laken and A.W. Wolfendale, Cosmic ray effects on cloud cover and their relevance to climate change, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.03.001.

  47. 47
    Jeff Pierce says:

    #36, CM: Cheers!
    #43, Edward: Yes, dust and other primary particles (e.g. soot, sea salt) can act as cloud condensation nuclei (CCN) too. Aerosol nucleation is not the only way CCN are formed. Both nucleation and primary emissions are important, but it varies from region to region. As you can imagine, dust may be the dominant CCN source in dust storms blown off of the Sahara.

    Thus, the impact of cosmic rays on CCN/clouds is also limited by primary emissions contributing to CCN. Even in the case where there is no nucleation (and thus no impact of cosmic rays on aerosol nucleation) there will still be CCN (albeit a reduced amount) for cloud droplets to form on.

  48. 48
    Paul S says:

    Hank Roberts – AR4 had this to say:

    Because the mechanisms are uncertain, the apparent relationship between solar variability and cloud cover has been interpreted to result not only from changing cosmic ray fluxes modulated by solar activity in the heliosphere (Usoskin et al., 2004) and solar-induced changes in ozone (Udelhofen and Cess, 2001), but also from sea surface temperatures altered directly by changing total solar irradiance (Kristjánsson et al., 2002) and by internal variability due to the El Niño-Southern Oscillation (Kernthaler et al., 1999). In reality, different direct and indirect physical processes (such as those described in Section 9.2) may operate simultaneously.

  49. 49
    SecularAnimist says:

    By the way, this CERN/CLOUD paper is already being touted by deniers in blog comments everywhere as the latest “bombshell” that “blows a hole” in the AGW “hoax”.

    Oddly, not one of those comments that I have seen bothers to explain exactly what the supposed “bombshell” is.

    Perhaps content-free “bombshells” are the latest weapon in the denier arsenal.

  50. 50
    David Beach says:

    There are repeated complaints about Recaptcha which I find unjustified. Cycling through the process, I can read at least 80% without difficulty, though this is an update on rather worse previous values, following the reformatting of the confusion parameter from blurred doubling to superposition of a sine wave.

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