RealClimate logo

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. 101
    Tilo Reber says:

    Jeff Pierce: “However, the comment is really stating that the CLOUD experiments could not reproduce atmospheric nucleation rates from sulfuric acid + ammonia + cosmic rays + water vapor, “The nucleation observed in the chamber occurs at only one‐tenth to one‐thousandth of the rate observed in the lower atmosphere.”.”

    And yet Svenmark’s data on Forbush decreases show a variation of liquid water in clouds of 6-9%.

    Jeff Pierce: “THESE missing components are what needs to be revised in our models, not the dependence of cosmic rays.”

    Given Svenmark’s Forbush results, are you sure that organics are not working in conjuntion with the smaller nucleation particles created by the GCRs to create CCNs.

    Jeff Pierce: “Therefore, some other component (e.g. organic vapors) needs to be included in order for the CLOUD experiments match atmospheric nucleation in their chamber. These are going to be the results from the next set of CLOUD experiments (which occurred earlier this summer), and they are foreshadowing these results.”

    Hopefully these experiments include cases of increasing GCRs alone, increasing organic vapors alone, and increasing the two of them together.

  2. 102
    Jeff Pierce says:

    #101 Tilo Reber. Yes, I agree that the FD data cannot be taken lightly. Please see my earlier comment (#34) on them. However, that isn’t what the “climate models will need to be significantly revised” comment was referring to. There is A LOT of interesting stuff in the CLOUD nature paper, its not only cosmic rays.

    Organics are generally required to grow nucleated particles to CCN sizes (and is included our models… albeit, there are many uncertainties regarding how much organics we should have), but what I was referring to here was organics in the nucleation process. This is what we are entirely lacking. Again, please see my earlier comment on FDs. There may be other mechanisms at work (e.g. the effects of ions on the freezing of cloud drops), and models may be lacking something important to explain them, but we really don’t know yet. The CLOUD results unfortunately haven’t changed that.

    Yes, the CLOUD experiments are very well organized such that the individual contributions of different components can be determined. I’m hoping we’ll continue to learn new information from the additional CLOUD experiments.


  3. 103
    Hank Roberts says:

    Jeff, when you say “organics in the nucleation process … is what we are entirely lacking” — do you mean lacking in the models?

    This review/summary says

    “… Understanding the aerosol budget in the absence of anthropogenic influence is necessary to establish a baseline aerosol forcing and provide a framework for models …

    … This special issue presents a snapshot of current research topics in this study area. It comprises twelve peer-reviewed open access articles spanning the full spectrum of atmospheric science research on this subject….”

    How does this sort of field work make its way into climate models?

  4. 104
    Jeff Pierce says:

    #103, Hank Roberts: Yes, I was referring to the detailed aerosol models that include nucleation. As far as I know, only one of these models (Ken Carslaw’s group in Leeds) has ran simulations with a nucleation scheme that includes organics.

    Are you asking how does research on remote and natural sources make it into climate models?

    In general there are 2 ways. (1) A research team publishes measurements of some chemical concentrations, a certain phenomena or some process. We test our models to see if we can represent what was observed. If the model does not represent this test, we try to see if we can better represent this process in the model (often it might be a good idea to work with the people who took the measurements). (2) The group who makes the measurements develops a parametrization, or representation, of the process for models. The models incorporate the process and test against observations.

    A nice example of these is in the special issue that you sent that editorial from ( There have recently been a wealth of new observations regarding natural organic aerosols from the ocean, (see the paper, “Primary and Secondary Organic Marine Aerosol and Oceanic Biological Activity: Recent Results and New Perspectives for Future Studies”), and we are beginning to incorporate these into the detailed aerosol models, (see the paper “Global Modeling of the Oceanic Source of Organic Aerosols”). If we find in the detailed aerosol models that the marine organic aerosol sources may be important for climate change predictions, we work with the groups in charge of IPCC models in representing these processes in their models.

  5. 105
    Hank Roberts says:

    Thank you Jeff Pierce, wonderful answer.
    I found another review article from 2003 that mentions more research areas I didn’t know existed, informative:

  6. 106
    Jeff Pierce says:

    Thanks, Hank. Indeed organic aerosols are a very hot topic in aerosol research. They involve on the order of 100s of different compounds with a wide range of chemical properties. And now we know that they are important for aerosol nucleation and the growth of these new particles to larger sizes where they can act as Cloud Condensation Nuclei (CCN). It may be useful to have a post on organic aerosols sometime in the future.

  7. 107
    melty says:

    Meow says: 24 Aug 2011 at 6:29 PM “Palle et al 2004 … Earthshine… albedo… ” Please. That study made for good press releases but the science was horribly flawed (e.g., along the lines of “Pinatubo? Where the hell is Pinaetubo?!”; “…sooooo, both the Moon and the Earth are Lambertian scatterers?!”. Almost wrote to the editor on that one.

  8. 108
    melty says:

    p.s. sorry for the typo (Pinaetubo). Didn’t we learn anything about aerosol formation from INDOEX?

  9. 109
    pete best says:

    James Dellingpole of the UK Telegraph (mainly right wing broadsheet although at times a good newspaper) who is renewned for his Anti AGW stance links svensmark and GCR to cloud formation and hence its the sun type arguments.

  10. 110
    Graham Stark says:


    Fitting a time trend through that Oulu data does indeed show a significant positive time trend:

    OLS, using observations 1964:07-2011:07 (T = 565)

    Dependent variable: adj_neu

          coefficient   std. error   t-ratio   p-value 

    const 6024.12       30.3929      198.2     0.0000   ***

    time  0.401073      0.0930483     4.310   1.92e-05  ***

    Mean dependent var 6137.623 S.D. dependent var 366.3152

    Sum squared resid 73263626 S.E. of regression 360.7364

    R-squared 0.031946 Adjusted R-squared 0.030227

    F(1, 563) 18.57931 P-value(F) 0.000019

    using monthly data from 1964/07 to 2011/07

    where time is a linear time trend (1964.07 = 1) and adj_neu is Oulu’s neutron count rates [counts/min] measure corrected for pressure and efficiency.

    I’m absolutely not an expert on this, though. Might just be an artifact of the choice of start/end periods, or something. And sorry about the formatting.

  11. 111
    Graham Stark says:

    Fitting a time trend through that Oulu data does indeed show a significant positive time trend:

    OLS, using observations 1964:07-2011:07 (T = 565)

    Dependent variable: adj_neu

          coefficient   std. error   t-ratio   p-value 

    const 6024.12       30.3929      198.2     0.0000   ***

    time  0.401073      0.0930483     4.310   1.92e-05  ***

    Mean dependent var 6137.623 S.D. dependent var 366.3152

    Sum squared resid 73263626 S.E. of regression 360.7364

    R-squared 0.031946 Adjusted R-squared 0.030227

    F(1, 563) 18.57931 P-value(F) 0.000019

    using monthly data from 1964/07 to 2011/07

    where time is a linear time trend (1964.07 = 1) and adj_neu is Oulu’s neutron count rates [counts/min] measure corrected for pressure and efficiency.

    I’m absolutely not an expert on this, though. Might just be an artifact of the choice of start/end periods, or something. And sorry about the formatting.

  12. 112
    greg says:

    It seems to me, a non-scientist, quite obvious that non-human factors have a play in regulating atmospheric biochemistry. CERNs experiments validate the connections between our planet and the larger cosmos. This is one of the reasons why I love life so much. I also feel that using this study to justify continued ignorance of sulphur and CO2 pollutants, especially given their massive increase over the last few centuries, is very dangerous.

    Basic (maybe dumb) question: GCR increase ionization towards creation of aerosols, right? Are CO2 and sulphur pollutants ionically charged or relatively inert?

    Thanks for the article (that I had to read about three times to begin to understand) and informative posts.

  13. 113
    Jim Groom says:

    I read the James Dellingpole UK Telegraph article, which was of course difficult to digest. However, more disturbing was reading many of the comments attached to the article. Truly astounding. The PR war is being won by the deniers, or so it appears from the public’s reaction to the Dellingpole trash.

  14. 114

    #112–I wouldn’t get too alarmed. A lot of news sites have their resident denialist trolls, and the reputation of the Telly would lead me to expect a bunch of them there. Most likely, the greatest number of the true ‘public’ pass by with barely a yawn. Which is both good and bad–they are far less influenced (IMO) by denialist propaganda than we might think (or they DO think, judging by the triumphalist rhetoric frequently bubbling up), but on the other hand we aren’t having all that much effect either.

    Or so it seems to me.

  15. 115
    Clippo (UK) says:

    Although off main topic, Re: #109,112,113

    Although a dedicated ‘alarmist’, I subscribe to the Daily ‘Bellylaugh’ – (‘cos I get it at half price )- and they have published 3 letters from me.

    In particular, 2 of them were very critical of AGW denier Christopher Booker who continually supports the anti-AGW cause and criticises UK efforts at Sustainability. However, Delingpole rarely appears in print – he seems to be Telegraph blog based, so those silly comments referred to there are just the only way nutty extremists can have a say.

    The main environmental reporters, Geoffrey Lean and Louise Gray are clearly pro-AGW and the Telegraph is working behind the scenes with Shell and Environmental groups to influence the UK’s future energy policy – see Age Of Energy on their website.

    So……. I suspect the Telegraph is doing what many other newspapers do – simulating ‘debate’ to increase sales.

    And, regarding Delingpole, I’m sure most UK readers here remember the BBC recently ran an interview with him in “Horizon – Science under Attack” by Sir Paul Nurse,(President of the Royal Society) and made Delingpole look an utter fool in the eyes of millions of viewers.

    I just hope the BBC now have the courage to present the CERN findings in an unbiased Horizon type program.

    (gi’ss a job )

  16. 116
    deconvoluter says:

    #109 includes some highly controversial phrases, some of which would be OT to explore here. I’ll content myself with the euphemism

    “anti AGW stance”

    which suggests a paper with contrary opinions rather than a host for major propagandists like Delingpole and Monckton.

  17. 117
    CM says:

    Graham Stark #110,

    I think you’ll find the significance you get using OLS is way inflated due to auto-correlation in the monthly data.

  18. 118
    Hank Roberts says:

    > Jeff Pierce says: 30 Aug 2011 at 6:23 AM
    > … organic aerosols … 100s of different compounds with a wide range
    > of chemical properties…..

    This reminds me of Crutzen’s Nobel lecture; he says: “Heterogeneous reactions on aerosol particles — The issue of interactions between gases and atmospheric aerosol is largely unexplored and very little considered in tropospheric chemistry models….”

  19. 119
    Jeff Pierce says:

    #111, Greg: Sulfuric acid vapor, which is formed by the oxidation of SO2 (a primary pollutant emitted from coal combustion and other sources) may become ionized in the atmosphere through GCRs or radioactive gases such as Radon. It is these sulfuric acid ions (along with perhaps nitric acid ions and ammonia ions) that are the ions that aid in aerosol nucleation.

    Sulfuric acid vapor in general (even in its neutral, non-ionic form) has long been known to be the main ingredient in atmospheric aerosol nucleation (and these CLOUD results continue to show this… nucleation goes to zero at low sulfuric acid concentrations, but nucleation did not go to zero when ion concentrations were low). Therefore, changes in anthropogenic sulfur emissions have a very large impact on nucleation rates (larger than the change in nucleation due to cosmic ray changes between the solar max and min).

    As far as I know CO2 does not greatly affect the ion concentrations of the atmosphere.

    #116, Hank: Nice find!

  20. 120
    Louis Derry says:

    Before people get all breathless about this study, it may be instructive to recall the chamber experiments on cloud seeding using iodide salts in the 1940’s. They unambiguously showed greatly enhanced water droplet nucleation, following on some theoretical considerations of the interaction of I and H2O, and the observation that aerosols could nucleate raindrop formation. Subsequent decades of research and experiment have not shown simple or reproducible results for cloud seeding. So the chamber experiments from CERN are nice, but it’s pretty clear that there is a very long way to go before or if the CLOUD results can tell us much about the real atmosphere. If you’re not a big fan of cloud seeding, best to hold off on GCR as the 21st century alternative.

    [Response: Thanks Lou for that cogent analysis. –eric]

  21. 121
    Edward Greisch says:

    “RealClimate has a good rundown of what Kirkby et al.’s results do and do not mean.”

  22. 122
    CRS, Dr.P.H. says:

    Chicago Tribune editorial:,0,7115731.column

    [Response: The guy seems a little confused as to what the CERN experiment is studying – aerosols or greenhouse gases? – but then it is only the ‘consensus’ that says these things are different… – gavin]

  23. 123
    Bengt A says:

    In figure S.4 (Supplementary material) one can clearly see the build up of particles to the size of + 40 nm. Why don’t they comment on that? Is this some other irrelevant process going on or are they saving this finding for a later paper?

    [Response: This is called a ‘nucleation event’ and happens far more haphazardly or randomly than simple nucleation of small particles. Jeff might know better, but I guess that this hasn’t happened sufficiently often to get any idea of whether it is more or less common or affected some other way as a function of the inputs. – gavin]

  24. 124
    gavin says:

    This is odd. The link that we had to the initial CLOUD concept paper (written in 1998) was:

    which was functional last week. However, this directory has since been scrubbed, and that link no longer works. Fortunately, Jasper Kirkby still has the document on his personal site:

    and of course, it exists in the google cache as well.

  25. 125
    Hank Roberts says:

    Looking there makes me wonder — could this have begun as an attempt to refute the idea that dimethyl sulfide is a feedback for creating clouds?

    Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate

    Robert J. Charlson, James E. Lovelock, Meinrat O. Andreae & Stephen G. Warren

    “The major source of cloud-condensation nuclei (CCN) over the oceans appears to be dimethylsulphide, which is produced by planktonic algae in sea water and oxidizes in the atmosphere to form a sulphate aerosol Because the reflectance (albedo) of clouds (and thus the Earth’s radiation budget) is sensitive to CCN density, biological regulation of the climate is possible through the effects of temperature and sunlight on phytoplankton population and dimethylsulphide production. To counteract the warming due to doubling of atmospheric CO2, an approximate doubling of CCN would be needed.”

    Not that it matters what the originators believed, as long as the work’s done fairly.

    But I find it odd that the CERN/CLOUD group seems to believe that organic material, if needed, could only increase but could not initiate the process, e.g.

    “The critical cluster size associated with nucleation is somewhere between 0.8 and 3.0 nm. Some studies have found that growth rates of particles from 3.0 nm to around 20 nm cannot be accounted for using condensation of sulphuric acid alone. Volatile organics compounds could account for some of this additional growth. …”

  26. 126
    Hank Roberts says:

    Oh, apparently it was a surprise.

    Compare this, particularly the illustrations for paleo climate change

    to this:
    “Cloud-making: Another human effect on the climate
    24 August 2011 by Michael Le Page

    IN HIS Gaia hypothesis, James Lovelock famously suggested that living organisms could affect clouds – and he was eventually proved right. Now it seems the effect may be even stronger than we thought. Organic vapours released by organisms such as trees, marine bacteria and livestock appear to play a far more important role in cloud formation than suspected.

    “This was a big surprise,” says Jasper Kirkby at CERN near Geneva…..

    Kirkby’s piece also refers to the ‘global electrical circuit’ affected by cosmic rays being involved in ionization and cloud formation.

    Has anyone looked for changes in clouds associated with radiation fluxes around earthquakes, as reported to show up in satellite detection of atmospheric electrical events, e.g.

  27. 127
    Jeff Pierce says:

    #123: Bengt A: You are right in thinking that this growth to 40 nm (and larger) particles is very important, and you are also right in thinking that they are saving this for a later paper. This growth process after nucleation is what bridges the connection between nucleation and CCN. They will do an entire new set of experiments to look at how these growth processes. In this first paper, they did a tremendous number of experiments to determine this information about nucleation (and time at CERN is very limited).

    In my group, we’ve theoretically calculated that the change in CCN due to cosmic rays is significantly smaller than the change in nucleation due to cosmic rays. For example, lets say that between the solar max and solar min, nucleation rates increase by 10%. We now have 10% more 1 nm particles, and these particles are all competing for condensible material (sulfuric acid and organics) so they can grow to larger sizes. Thus, the particles grow more slowly when nucleation is increased (all else fixed) Generally the smallest particles are lost by coagulation (colliding with other particles) more quickly than larger particles, so by keeping these particles small for longer, they are more likely to be lost by coagulation. Finally, coagulation will also increase due to the increase in the total number of particles. Thus, we find CCN increase by significantly less than 10%.

    Since (as far as I know) only theoretical calculations of this growth exists, it will be great to see what the results from the CLOUD experiments on aerosol growth show. They may confirm our calculations, or they may find that there were some physical details that our model was not capturing.

  28. 128
    Hank Roberts says:

    Crutzen, in his Nobel speech, also said:

    “… the seriousness of this global problem has been recognized by all nations of the world …. Although the cause-effect relationship is very clear, for the layperson as well, it is depressing to see that it is, nevertheless, not accepted by a small group of very vocal critics without any record of achievements in this area of research. Some of these have recently even succeeded in becoming members of the U.S. Congress.


    … I can only conclude that mankind has been extremely lucky …. we should always be on our guard for the potential consequences of the release of new products into the environment. Continued surveillance of the composition of the stratosphere, therefore, remains a matter of high priority for many years ahead.”


    Hey, what’s the worst that could happen? Hmmmm ….
    May 14, 2007 Astrochemistry Probing Titan’s Smog

    “… it appears that ion-neutral reactions occur in the upper atmosphere to produce polycyclic aromatic hydrocarbons (PAHs) as well as heterocyclic compounds involving nitrogen…. methane, cyanogen, benzene, and other organic molecules up to 100 daltons…. larger molecules such as naphthalene, anthracene derivatives, and an anthracene dimer…. heavy negative ions, with masses up to 8,000 Da, probably produced by aggregation of PAHs.
    ‘These very large organic molecules in the upper atmosphere indicate there’s a complex ion-neutral chemistry going on that really hasn’t been considered much before,’ says Caitlin Griffith, an associate professor of planetary atmospheres at the University of Arizona.
    Those massive negative ions—no longer in the gas phase, as compounds heavier than about 2,000 Da become aerosols in Titan’s atmosphere—then likely lose altitude, becoming condensation nuclei for supersaturated benzene and other components of Titan’s atmosphere. As the particles grow and react, eventually they might become tholins, large hydrocarbon-nitrile particles thought to produce Titan’s orange haze….

    —–end excerpt—–

    Seems like any variation in the solar/interplanetary magnetic/cosmic ray environment ought to show up in Titan’s atmosphere.

    Anyone looking?

  29. 129
    Bengt A says:

    #127 Jeff Pierce

    Thanks for the comprehensive answer!

    So, based on fig S4, one can say that the CLOUD experiments shows that cosmic rays seeds aerosols that grow into CCN:s, though the question is still out whether this process has any relative importance compared to other ways to grow CCN:s (hope I got that right). It will be interesting to read coming papers from CLOUD!

  30. 130
    Jeff Pierce says:

    #129, Bengt A: Yes, this is essentially right. And I too am looking forward to the upcoming CLOUD papers.

  31. 131
    Snorbert Zangox says:


    Again, you refuse to understand my point. First, I said nothing about NOx, I mentioned only NO2. The sulfuric acid concentrations during the CERN experiments were on the order of 0.1 ppb. There is far more sulfur dioxide than that in a normal atmosphere. At relative humidities above 20%, NO2 will oxidize that sulfur dioxide quickly and completely to sulfuric acid. The CCN available to create cloudiness will be at least an order of magnitude higher than that used during the CERN experiments. Plus, CERN did not include other, naturally occurring particles.

    It seems certain that the ionization effect will be far greater than that which occurred during the CERN work.

    [Response: NOx is the sum total of NO and NO2 and since these species are almost always in equilibrium with each other (depending on sunlight/ozone etc), it is a normal shorthand to talk about NOx rather than each species individually. As for ambient concentrations of H2SO4, other sources suggest 10^7 molecules per cm3 – right in line with the CLOUD experiments. But if you have better information, provide some links – this is not my area of expertise and so I’m happy to learn (and please turn down the snark; it is not an inducement to engage). – gavin]

  32. 132


    SO2 is oxidized in the gas phase by the hydroxyl radical (OH) and in the liquid phase (i.e. cloud droplets) by H2O2 or O3 if I remember correctly, dependent on pH. NO2 may play a role here as a precursor to ozone.

    General comment: New Scientist features this study here: (with a citation from yours truly)

  33. 133
    Theo Kurtén says:

    Snorbert: NO2 does not react with SO2, check the NIST chemical kinetics database:

    the reaction rate is ridiculously small, and will never matter. The only known and well-established gas-phase oxidant of SO2 in the atmosphere is OH, as Bart pointed out – though there may be a couple of others in some circumstances. But not NO2 (or NO3 for that matter). NO2 *does* help regenerate OH consumed in hydrocarbon oxidation in polluted conditions, by acting as a O3 precursor. (O3 in turn is needed to produce excited-state oxygen atoms which react with H2O to give 2 OH). Perhaps this is what has confused you? But this will not really affect CLOUD results. (Incidentally, SO2 in the atmosphere normally has a lifetime on the order of days, so your claim of “quick and complete” conversion to H2SO4 is anyway incorrect, in addition to the fact that you have got the chemistry wrong.) I suggest taking a look at an atmospheric chemistry textbook, e.g. Dan Jacobs book:

    Chapter 13 describes the sulfur chemistry quite concisely.

  34. 134
    Cos says:


    Given the exponitial speed and advancement of our computer knowledge since since 1940, it could be soon than you think.

  35. 135
    Pete Dunkelberg says:

    Dust. Black carbon dust in the air, microphysics of: Jacobson is all over it. H/t Bob Wallace at the Sea Ice Blog.

  36. 136
    Brian Dodge says:

    Isn’t there a kind of Liebeg’s law for cloud formation, in that if there isn’t enough moisture to (super)saturate the air, then it doesn’t matter how many GCRs, SO2, H2SO4, PAHs, soluble/insoluble/amphoteric/surfactant organics, or pixie dust is in the air, there won’t be clouds magically formed(well, maybe with pixie dust &:>)? Also, decreases in CCN formers in clear sky won’t cause negative cloud formation.

    Conversely, if there’s enough water vapor but not enough CCN precursors, or less active precursors, then the level of supersaturation will have to go higher to start cloud formation. But, with DMS from plankton, and dust from the Bodélé Depression and other desert areas(which stimulate plankton when they rain out into the ocean), plus particulates from biomass burning and anthropogenic sources, and GCRs which have fluctuated only about plus or minus 10% since at least the 60’s, lack of CCN precursors are less likely (IMHO) to limit cloud formation – which puts nonlinearities into the process.

    It also seems to me that more GCRs might lessen cloud cover by increasing the rate of particle coalescence into rain. For every positive ion that’s created when an atom gets smacked by a cosmic ray, there’s a free electron that will want to attach itself somewhere. Both positive and negative charges will create mirror surface charges on conductive liquid particles, and most cloud particles will have acid, or salts dissolved in them. Once a particle acquires a net charge, it will attract other charged particle of the opposite sex, and through charge mirroring, neutral swinger particles that can go both ways. More charge pairs at high GCR rates might make the process of coalescing into rain more efficient and faster, reducing the amount of cloud “in the pipeline” between cloud formation and precipitation.

  37. 137
    wush says:

    If atmospheric co2 enrichment enhances the growth and reproductive abilities of the biosphere there must also be an increase in BVOC’s from the whole system. e.g. more DMS from phytoplankton and the huge amount of additional VOC from man made conifer plantation in the form of isoprene and terpenes and the rest;-

    “Bvoc’s constitute “one of nature’s biodiversity treasures.” Comprised of isoprene, terpenes, alkanes, alkenes, alcohols, esters, carbonyls and acids, this diverse group of substances is produced by a variety of processes occurring in many plant tissues.”

    and also solid particulate material (with the potential to form CCN), for example more pollen from healthier green photosynthesising plants and waxy leaf particles after decomposition.
    This additional aerosol loading could and should be taken into account.Is it Anthropogenic in origin,due to our co2 enrichment,although it is from natural sources?
    Ionisation by space energy and chemical reaction from solar light energy etc. just has more stuff to play with due to Humans putting more stuff in the atmosphere.
    Does this hold water?

    [Response: Possible but very difficult–practically impossible I’d guess–to demonstrate. You have many other factors affecting global plant biomass that would likely swamp out any such effect, land use/cover change being the biggest such. Also, CO2 fertilization does not necessarily lead to higher amounts of biomass–it likely leads to higher NPP, but that is a rate not a pool, and it doesn’t even necessarily do that, depending on the status of various other potentially limiting factors, climate conditions and such–Jim]

  38. 138
    Hank Roberts says:

    wush, look up “claw hypothesis” — I think that’s what you’re describing.
    Or here:

    > very difficult–practically impossible I’d guess–to demonstrate

    Gack, that would be sad indeed. People seem to be trying to model this along with all the other things mentioned, tho’ just beginning to do that.

    [Response: I was only referring to the amount of VOC that can be attributed to CO2 fertilization. People are definitely working on VOCs from various angles.–Jim]

  39. 139
    David B. Benson says:

    Brian Dodge @136 — In my amateur understanding, it suffices to have saturation has there always seems to be enough CCNs (except possibly in interior Antarctica, where it doesn’t matter). So until there is so much water vapor that CCN availablity becomes some form of limiting factor it suffices to just consider the water cycle. Now availability must be very high indeed when one considers the precipitation rates in parts of Pakistan in the summer of 2010.

  40. 140
    Hank Roberts says:

    > DMS
    Thanks, Jim, that makes more sense.

    Found a fairly big study report here:

    Many different projects under that umbrella. One small excerpt follows:
    The GLOMAP modelling project (led by Ken Carslaw) has, for the first time, quantitatively linked the seasonal cycle of cloud condensation nuclei (CCN) in the marine boundary layer with DMS dynamics using a global aerosol microphysics model. The sensitivity of CCN to local DMS emissions is lower (but the effect more widespread, over thousands of km) than previously thought due to long range transport of aerosol through the global free troposphere (see Achievement 3.3).
    GLOMAP also found that there is a significant source of marine organic aerosol (comparable in magnitude to the fossil fuel organic carbon source), and that stratospheric ozone depletion has driven increases in southern hemisphere winds – leading to increased sea spray, aerosols and CCN concentrations. The change in summertime forcing of – 0.7 W m-2 is comparable in magnitude, but opposite in sign, to the greenhouse gas forcing over the same period…..

    Makes me again wonder why the CERN physicists were surprised to find they might need more than nitrogen and sulfur to make clouds. Oh well, nobody can read everything.

  41. 141
    charles "chick" keller says:

    In terms of whether or not -25C I think I recall that Svensmark et al could only a correlation of GCRs with low clouds. If this is so then the larger lab CLOUD results at -25°C is not what we’re seeing?

  42. 142

    Hank et al,

    the following paper is relevant to what you’re discussing:

    “A review of natural aerosol interactions and feedbacks within the
    Earth system”

    by Carslaw et al

  43. 143
    Ray Ladbury says:

    Brian Dodge,
    Not Lieberg’s law as such, but rather a rate constant, or underlying both, the principle of detailed balance. It ain’t magic. Reactions consume reactants in given proportions. The proportion that is lowest wrt that ideal proportion limits the reaction. CCNs are not the limiting factor in cloud formation. Svensmark would have flunked P Chem.

  44. 144
    Ray Ladbury says:

    Snorbert Z.: “It seems certain that the ionization effect will be far greater than that which occurred during the CERN work.”

    I would put that right by the Nicean Creed as a statement of faith…well except the Nicean Creed would probably have more scientific basis. Dude, please crack an elementary chem text. Look at some reaction rates. Sheesh!

  45. 145
    Richard bird says:

    Some layman questions possibly heretical

    Has any possible cloud seeding by co2 molecules been considered?
    (the unsubtle gist of my question should be obvious)

    In the initiating post at top: “… and that given that change in cloud properties, you would need to show that it had a significant effect on radiative forcing”
    My understanding of the paper is that it shows that ionisation can increase cloud formation. If that applies to low level clouds, then does not the upwardly reflective effect of clouds simply reduce incident energy on earth surface? In which case, is not effect on radiative forcing irrelevant?

    Last, heat moves from a hot body to a cold space. The earth core is at 7000 deg c. Heat must pass out through the oceans and air and eventually into space. Nuclear events and heat generation within the earth may be as variable as sunspots. I don’t believe there is much data on this. Do Climate models assume earth heat emission to be constant?

  46. 146
    CM says:

    Richard Bird,

    Questions are, by definition, never heretical. But sometimes they are confused or irrelevant. Let me try some layman answers.

    1. CO2 gas molecules are some three orders of magnitude smaller than cloud condensation nuclei (CCN). The CO2 that is, in fact, used in cloud seeding takes the form of dry ice crystals.
    2a. Your understanding of the paper is wrong. It does not show that ionization can increase cloud formation, but that it can increase nucleation. As the original post pointed out, there are several steps from there to increased cloud formation.
    b. A change in cloud reflection to space is a radiative forcing.
    c. Yes, low clouds tend to cool the planet (in daytime), high clouds to warm it. The paper does not show that there will be more clouds, or if there are, that they will be low.
    3. Geothermal energy changes on geological timescales. Anyway, it heats the planet with some 0.08 W/m2, five orders of magnitude less than solar and two orders of magnitude less than the forcing from a doubling of CO2.

    Hope this helps.

  47. 147
    Richard bird says:

    CM thank you for the corrections, especially on the definition of radiative forcing.

    Co2: forgive my natural curiosity. Has there been any study of whether free CO2 molecules have any tendency to clump into crystals at the low temperatures of higher altitude?

    Re earth heat transfer: geothermal energy changes on geological timescales. Heat transfer is a constant 0.08 W
    /m2. Understood. Do climate models include consideration of shorter period heat releases such as from submarine volcanoes?

  48. 148
    Hank Roberts says:

    “Richard bird”
    — co2 freezing?
    — volcanoes?
    No measurable effect globally for individual events; no trend over time:

  49. 149
    Jeff S. says:

    I am a fervent reader of this blog as well as skeptic blogs such as Climate Audit and Watts up with that. I am also a follower of Richard Lindzen’s work as well as a few other skeptical climate scientists. I am looking for help to better understand the nature of the science behind positive forcing from CO2.

    Here is what I have trouble with as a scientist who is outside of his field and lacks detailed knowledge of many of the intricate and complex topics within this field. I don’t understand how the scientific method, the only tool we have at our disposal to determine cause and effect relationships, is used when climate modellers asses the impact of CO2 on cloud formation, water vapour and other known factors that effect climate sensitivity. The recent work out of CERN as well as some of Gavin’s posts give me more doubt about the methodology. Here is why:

    In a recent paper by Richard Lindzen he claims that if one were to take into account just the effects of CO2 without the potential impact of CO2 on other factors that a doubling of atmospheric CO2 would cause a 1 degree C global temperature increase. However, most models predict the impact of CO2 to be much larger due to its influence on other factors. On what bases methodological bases are these predictions made and by what measure are they tested? If, as the CERN study demonstrates, there are unknown variables that contribute to cloud nucleation where does one gain confidence in scientist’s ability to make predictions about the effect of increased CO2 on cloud formation in the real world. There is no process by which it is possible to test the effects of CO2 on cloud formation or water vapour in a system we don’t fully comprehend and have no ability to control. In other areas of science the bar to be able to make a publishable claim seams to be set much higher.

    Moreover, as Gavin has said repeatedly, we have no idea what the feedback is of cloud formation on temperature change. Jury is still out. Yet it is these unknown variables that are determining the predictions of CO2 on global warming. It is precisely these mechanisms that are being used to predict feedforward warming from CO2.

    What type of science is there (and where can I find it) to demonstrate to me why I should believe that a double of CO2 will produce more than a 1 degree C temperature change? What is Eric so certain about?

    [Response: Many things can affect climate. Let’s take an extreme example – a big asteroid like the one at the end of the Cretaceous. Now there are obviously many unknowns about exactly what happened. But those unknowns don’t impact our understanding of the role of CO2 (or ozone, or volanoes or solar changes, or land use change etc.) one jot. There is no zero sum game that says that the more we understand about driver X, the less we understand about CO2. The CERN experiments were related to aerosol nucleation and do not impact the constraints on climate sensitivity at all (if you disagree, please show me the paper that uses knowledge about aerosol nucleation at the nanometer stage as part of the argument for climate sensitivity). They are different issues. – gavin]

  50. 150
    Theo Kurtén says:

    Richard: CO2 clustering has been speculated to play a role in cloud formation *on Mars*, and hence has been studied quite a bit. As illustrated in the link by Hank Roberts, temperatures anywhere in the Earth’s troposphere are too high for this to occur.