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An incremental step blown up

New results from the University of Aarhus in Denmark and the Danish National Space Institute allegedly show that particles from space create cloud cover, according to a recent press release. And the Physics World magazine (May, 2011) report that the

researchers say this is the best experimental evidence yet that the Sun influences the climate by altering the intensity of the cosmic-ray flux reaching the Earth’s surface.

Quite spectacular claims! So let’s see what is the source of this information.

The basis for the statements was a recent paper published in GRL by Enghoff et al. The key points in the paper are stated as: (a) Cosmic rays increase nucleation rate, (b) A particle beam is not needed, for experiments, and (c) Ions are important for atmospheric nucleation rate. But where is the link to real clouds?

The word ‘cloud’ is mentioned in the paper. In the introduction:

Aerosol and cloud research is one of the most critical frontiers of climate science [Shindell et al., 2009; Bodenschatz et al., 2010] and the direct radiative forcing and indirect cloud albedo forcing from aerosols remain the dominant uncertainty in the radiative forcing of the atmosphere

The word ‘cloud’ is also found in some of the titles of the publications in the citation list. And that’s it.

OK, so this study is really about a laboratory experiment. The results presented are of the impact of ionization on the formation rate of aerosols with size ~4 nanometers (nm), as shown in the figure below:

Figure 1 from Enghoff et al, 2011

Figure 1. Formation rate of 4 nm aerosols versus ion concentration (Figure 1 in Enghoff et al).

Enghoff et al claim that the figure shows a clear contribution from ion-induced nucleation and considers this to be the (quoted from the paper’s abstract)

first unambiguous observation of the ion-effect on aerosol nucleation using a particle beam under conditions that resemble the Earth’s atmosphere.

Not so fast!

There is a significant amount of aerosol formation taking place with no ionization (“background levels”), and when the sample air in the experiment was replaced, this caused a large jump (seen as a shift along the vertical axis) in the formation rate (the different colours in the figure above). This clearly shows that the formation rate is also highly sensitive to factors other than ionization.

The figure further shows that the relationship between the ionization and the aerosol formation is not all that strong. There is a relationship, but there is substantial scatter and the slopes of the best fit are not very steep.

So let’s look at the clouds data. Is there a clear 11-year cycle in the cloud cover? The figure below presents the global low cloud cover from the ISCCP project. Perhaps there is an 11-year cycle embedded in the evolution since 1983, perhaps not. However, the variations in the evolution are clearly not dominated by 11-year cycles.

Figure 2. ISCCP analysis of global low cloud cover from IR-channel.

We see the same thing in a study by Harrison & Stephenson (2006), which provides an additional clue based on diffuse light, which is light scattered by clouds. They do find a link between cosmic galactic rays (GCR) and the diffuse light (figure below), suggesting a link between the GCR and cloudiness. But when you look at the scatter plot, the link is not very visible (if you ignore the fitted lines). The reason for this is that this link is very weak.

Figure 3. Scatter plot of the daily mean diffuse light fraction measured in Jersey (y-axis) plotted against Climax daily average neutron count rate (x-axis). Reproduction of Harrison & Stephenson (2006), Fig. 2a.

There has been a number of studies on the relationship between solar activity and earth’s climate, suggesting there is a solar signal. But the solar influence seems to be weak. GCR don’t come from the sun, but are charged particles from distant galaxies and stars that are modulated by the solar magnetic field. The solar magnetic field is closely linked to solar activity.

Figure 1 here may be consistent with a weak relationship between GCR and clouds, due to a substantial scatter, weak trend (not very steep slope), and the pronounced effect of changing the air supply.

It is conceivable that turbulent mixing of the air will produce small pockets of air with higher formation rates, in a same fashion as air with different impurities did in the experiments of Enghoff et al.

However, there is another reason why there really is a weak link from Enghoff et al.’s results to clouds. The experiment conducted by Enghoff et al. examined the formation of ultra-fine aerosols with size of 4 nanometers. But clouds need particles of the size approximately 10000 nanometers (10 micrometers) to form cloud drops for air that is barely supersaturated, according to the Köhler curve (which is central to cloud micro-physics).

What happens between the stage where 4nm aerosols form and the stage where they becomeact as CCNcloud drops (with a ~10 micrometer radius) is unknown (see Figure 4 for a depiction of these two stages). The aerosols must grow and become an order of million times larger in terms of their initial volume.

Figure 4. Comparison between ultra-fine aerosols with 4 nm radius (red) and cloud drop with 10 micrometer radius (blue). The ultra-fine aerosol is almost invisible compared to the cloud drop on the left, so a blown up version is shown on the right.

It is interesting to note the way the word “climate” appears in the GRL paper (3 times: once in the introduction and twice in the titles in the reference list) and the Danish press release (15 times, counting phrases such as ‘climate chamber’ and ‘climate researcher’). The press release claims that the results

substantiate the connection between the Sun’s magnetic activity and the Earth’s climate

and that

there is much to indicate that climate models must hereby take cosmic radiation into consideration.

It is difficult to explain any long-term change in our climate in terms of the hypothesis that GCR affect clouds, having an effect on the albedo, and ultimately the temperatures. For starters, we see no evidence for any long-term change in the sun in the last 50 years (light blue and red curves in Figure 5 below) or in the GCR measurements (grey symbols in Figure 5).

Figure 5. Time evolution of the global mean temperature (upper blue curve), forcings associated with CO2 (green), galactic cosmic rays (grey; from CLIMAX and plotted as -1x GCR), total solar irradiance (light blue), and the sunspot number (red, bottom)

So my take on this, is that the paper only really shows that the nature of the ionizing particles is not important for the ion-induced component of the nucleation. Does this imply that the cloud experiment at CERN is necessary? I wonder. But key point (c), that

ions are important for atmospheric nucleation rate

is not supported by the evidence presented in the paper. Ions play a role, but Figure 1 does not really suggest they are important. The most problematic aspect of this story is that I find it difficult to explain how the Danish press release can be based on science but on is more like wishful thinking.

57 Responses to “An incremental step blown up”

  1. 1
    Erik says:


    While I totally agree with the overall message of this post, I think that your stated CCN size is too high. There are very few 10 micron particles around and typical CCN sizes in the real atmosphere are 200-500 nm.

    [Response: Right, but they need to grow ~ 10 micron to form cloud droplets. The process, as you indicate, is complex, involving more than one phase, such as the condensation of water vapour. -rasmus]

  2. 2
    Marco says:

    Rasmus, I had the same idea when I first saw the press release: wishful thinking. Internal Danish issue perhaps, showing you don’t need CERN (and why didn’t Svensmark talk to them, eh?).

    Minor quibble: there seems to be an error in the last science:
    “how the Danish press release can be based on science but on wishful thinking”

    [Response: The rumours say that Svensmark no longer is a part of the CERN team. -rasmus]

  3. 3

    Hi Rasmus,

    Great context work here and much appreciated. The nuances of their method and usage of cloud and climate are certainly indicative of intent. Too bad the media can’t, or won’t, parse the reality from the inference or intent.

    Looks like yet another Svensmark styled piece with overtones of lost leaders and red herring messaging.

    Of course, some call it science :)

  4. 4
    ellenlee says:

    [edit spam]

  5. 5
    Alex says:

    Just to clarify what Erik and Rasmus are talking about in the first response. 4nm particles cannot serve as cloud condensation nuclei at all. They aresimply too small and the curvature effect (associated with surface tension) imposes that the supersaturation needed to activate them is huge and does not occur in the Earth’s atmosphere. See, for example, the Köhler curves at
    They show clearly that in order to “activate” an aerosol, the supersaturation is not very big only when its dry radius is on the order of several tens to a few hundreds of nanometers. We must have in mind that this would imply that the particles generated in the experiment would have to experience a growth on the order of 10^4 to 10^6 (in dry conditions) for them to become CCN. We must remember that are a number of aerosol sources that produce particles of this size (about 100 nm or 0.1 micron), including anthropogenic ones.
    Once activated, the instability shown in the Köhler curve implies that the condensational growth takes over and the newly formed cloud droplet quickly reaches the size of few microns, as the ones we find in shallow cumuli. However, since the rate the droplets grow by condensation is inversely proportional to the own droplet radius, other processes are needed to precipitation-size particles to form (collision-coalescence and ice-phase processes).

  6. 6
    CM says:


    While on the subject: Could I ask your take on Erlykin et al. 2011, in particular their finding that any effect of cosmic radiation is limited to 1% of cloud cover, and their estimate that any temperature increase due to such a mechanism over the past 50 years of barely changing CR is limited to 0.002 °C?

    Meanwhile, I’m enjoying how the Aarhus press release suggests a steel bucket in a lab gives you a direct view of what goes on in the atmosphere.

    Press release (emphases added): …scientists have succeeded for the first time in directly observing that the electrically charged particles coming from space and hitting the atmosphere at high speed contribute to creating the aerosols that are the prerequisites for cloud formation.

    Paper: The experiments took place in a 1 m long, 50 L cylindrical, electropolished stainless steel reactor… A low‐intensity beam of 580 MeV electrons from the Aarhus Storage Ring ASTRID… at the University of Aarhus was used as the ionizing source.

    Press release: With the researchers’ new knowledge, it is now clear that here is a correlation between the Sun’s varying activity and the formation of aerosols in the Earth’s atmosphere. Initially, the researchers have demonstrated that there is a correlation…

    Paper: …

    (Does a correlation between ionization and aerosol formation in a lab experiment “demonstrate” a correlation between solar activity and aerosol formation in the atmosphere? I think they have demonstrated a mechanism, which supports a plausible hypothesis that there should be such a correlation — to be tested against solar and atmospheric data. Or, alternatively, if such a correlation has been demonstrated — again, the paper does not say — it suggests a plausible causal relationship to account for it. But maybe I’m being overly pedantic here?)

    [Response: For Erlykin et al. 2011, see the post ‘Still not convincing‘. -rasmus]

  7. 7
    CM says:

    Marco #2, Svensmark is one of the et al. on this paper.

  8. 8
    Jonathan Gilligan says:

    Stepping back from this specific paper to the big picture, has any proponent of the cosmic ray/CCN hypothesis addressed the fingerprinting question? What does the cloud hypothesis imply regarding spatiotemporal patterns (stratospheric cooling, nights vs. days, etc.)? It seems to me that people advancing unconventional hypotheses tend to focus on one or two details and never ask how their hypothesis fits the big picture.

  9. 9
    Bill Hunter says:

    “it suggests a plausible causal relationship to account for it. But maybe I’m being overly pedantic here?”

    That will certainly be necessary.

  10. 10
    Eli Rabett says:

    The most interesting thing about aerosol growth to Eli is the role that SOx plays. Cleaning the air, at least locally, strongly affects cloud cover (see the Molina’s work in Mexico City, and Monet’s pictures of Parliament), and there is also something obvious there WRT volcanos. A much more direct and convincing part of the mechanism. Clean air is air without much SOx and that must have effects on global temperature.

  11. 11
    Nick Berini says:

    “Stepping back from this specific paper to the big picture, has any proponent of the cosmic ray/CCN hypothesis addressed the fingerprinting question? What does the cloud hypothesis imply regarding spatiotemporal patterns (stratospheric cooling, nights vs. days, etc.)? It seems to me that people advancing unconventional hypotheses tend to focus on one or two details and never ask how their hypothesis fits the big picture.”

    I would also add that a major missing piece from this argument (and many others) is – OK, so why is CO2 NOT causing the warming effect physical theory suggests it should? Lost on some, but there is just a whole ton of evidence to overcome / “fit” when trying to overturn a well established theory…

  12. 12
    Dirk McCoy says:

    Thanks for publishing this, there are folks who denigrated the work of scientists that claimed a solar-climate(temperature) link because the variability in solar energy output just wasn’t enough to explain the temperature swings, and perhaps they now realize that there could be another mechanism- similar to a transistor where small changes in gate voltage can affect large changes in power transmission- whereby solar activity can create significant effects on temperature.

    And this is why CERN is necessary- because it carries a bit more weight in scientific matters- and they are working to understand the unknown mechanisms of how 10 micron particles nucleate from smaller particles (and nucleate from smaller particles they obviously do, how much cosmic rays affect that is unknown).

    And as this knowledge is disseminated and better understood, eventually we’ll have better models, and can achieve more widespread adoption of them- if the solar/cosmic ray/cloud mechanism is significant it could explain why temperatures in neither hemisphere are proceeding upwards lock-step with IPCC forecasts- and opening the door for a more accurate and widespread acknowledgement of CO2 effects on temperature and climate.

  13. 13

    1) What happens to very small droplets ~ 4 nm? They evaporate.

    2) Most actual atmospheric cloud droplets form around dust particles including bacteria, rather than starting from minute droplets of pure water. This increases the radius of curvature and gets around the Köhler curve problem. A charged dust particle ought to work even better.

    As alluded to by Eli, SO2 in air oxidizes to SO3 which has a very strong affinity (to use an ancient term) for water, becoming H2SO4 just for starters. How many have enjoyed pouring H2SO4 into a beaker with a centimeter of sugar on the bottom? This affinity can sharpen the Köhler curve.

  14. 14
    Marco says:

    CM, thanks [mental note: do not ignore authors when looking at a paper]. Suddenly Rasmus’ comment on CERN and Svensmark makes more sense. And the overinterpretation also makes more sense.

  15. 15

    Great post. I miss these sorts of posts, they’re too few and far between, but then science can’t be expected to move as quickly as American Idol episodes, can it? If only climate existed purely for my own personal intellectual stimulation and entertainment!

    But this is great stuff, and it’s enlightening to see how some are guilty of not of actual bad science, but at least pushing the envelope, when the denialsphere is always abuzz about bad techniques, exaggerated conclusions or preplanned outcomes by “AGW proponents”. Between things like this, and Wegman, I don’t know why they don’t just back off and admit that scientists are human, the process can’t be perfect, and that this sort of dueling is exactly how science works and needs to work (because all good scientists are both passionate and fallible).

    Will anyone be submitting professional comments to GRL on the paper, with the points mentioned here?

  16. 16

    This brings cloud chambers to mind. How does the air in the chamber stay supersaturated? Or does it?

  17. 17
    chris says:

    re Dirk 27 May 2011 at 10:37 AM

    One of the things we know with very high certainty is that changes in the cosmic ray flux (CRF) can have made no significant contribution to the very marked warming of the last 30-odd years. There has simply been no trend in the CRF during this period.

    Likewise the CRF is presently higher than it’s been since since direct measures began

    (see fig 1)…….and yet 2010 was the warmest year on record in the GISS analysis. Clearly the notion that changes in CRF have significant effects on climate is sorely lacking an evidence base. It’s very unlikely that experiments in artificial mimetics of Earth’s atmosphere in “cloud chambers”, whether or not these are attached to particle accelerators, will change this extant fact.

  18. 18
    chris says:

    A further point on Harrison and Stephenson (Figure 3 in top article):

    (i) Harrison and Stephenson show (see their Figure 2; reproduced in Figure 3 in top article) a very weak correlation between the CRF and the diffuse fraction (DF) (cloudiness – presumably dominated by changes in low-level cloudiness), which breaks down when the CRF is higher than 3600 (x100) per hour. Above this level the DF is independent of the CRF.

    (ii) Taken at face value, this seems problematic. Examination of Harrison and Stephenson’s Figure 2 indicates that most of the data in their analysis period (1968-1994) lies in this non-responsive region of the CRF/DF “correlation” where the CRF and DF are apparently completely independent (no correlation). If one examines the entire CRF record, that is reinforced. During around 90% of the entire period between the start of the CRF count (1951) to now, the CRF has been higher than 3600 (x100) per hour [if one looks at the climax CRF/sunspot number plot on the page I urled and compares this with the data in the downloadable datasets on that page one can work out that a CRF count of 3600 (x100) per hour corresponds to around the 83% level].Again one might conclude that that’s additional explanation for the complete absence of a detectable CRF (solar) contribution to the marked warming of recent decades.

    (iii) This leads to an additional problem, which relates to ascribing CRF climate effects to earlier periods. Although we’re just coming out of a marked solar minimum right now with respect to the solar cycle, the sun is in a relatively “strong” state. If one examines the sunspot data going back to 1600, this is apparent. Now if the very strong inverse relationship between CRF and sunspot number (see Climax neutron/sunspot data urled above) was maintained in those periods (no reason to think otherwise), then the CRF was likely generally stronger [greater than 3600 (x100) per hour] during periods like the Maunder and Dalton minima. However taking Harrison and Stephenson’s data at face value, the cloudiness as measured by the DF is completely independent of the CRF at values above 3600 (x100) per hour. Therefore the CRF cannot have played a significant role in the cooling during those periods.

    (iv) We could deal with that problem by making some ad hoc assumptions. Perhaps the CRF became decoupled from the other solar parameters during periods with “weak” solar output. Perhaps the thresholds for a CRF-cloud correlation was higher then than it has been for the past 40 years (one might imagine that in periods where the air is rather clear of man made aerosols, the threshold for CRF effects on cloud formation become higher…and so on). But there’s no evidence for any of these ad hoc assumptions.

  19. 19
    Edward Greisch says:

    16 Pete Dunkelberg: Roger that. If we are living inside a Wilson cloud chamber, why don’t we see the cosmic ray streaks all the time?

    Answer: There is enough dust around to form more than enough condensation nuclei. Earth’s air never supersaturates without human intervention. The weather forecaster has never said: “The humidity is 400%.” Living would be really hard if the humidity could be 400%. Sweating wouldn’t cool you because you would be the condensation nucleus. Hot water would continually condense onto you, overheating you.

    4 nm particles can’t compete with the huge availability of large dust particles even if 4 nm particles could be condensation nuclei, which they can’t.

    Thanks for helping me answer this question.

  20. 20
    chris says:

    Pete Dunkelberg

    Cloud chambers are maintained in a supersaturated state, whereas the lower troposphere generally isn’t. The latter has lots of cloud condensation nucleating species over forests and oceans (dimethylsulphide from phytoplankton).

    None of these real world parameters are reproduced in the cloud chamber experiments, however huge the amounts of money invested in the CERN experiments…

  21. 21
    Russell says:

    The General Theory of Factoid Genesis suggests this falsifiable hypothesis:

    Before the year is out, the doorsteps of Tony Watts and Marc Morano, and Heartland revival meetings will be overrun by Sideshow Bobs bearing wheezy bits of apparatus designed to put the fear of cosmic rays into the audience.

    Lecture demonstration Cloud Chambers now gathering dust on venerable lab supply firm shelves will be fired up as as proof positive that clouds, not CO2 rule the …..( fill in rest of Fred Singer’s lines here).

    Viral videos of foggy tracks traversing copper cylinders will appear shortly thereafter, exhorting the Buck Rogers rerun-watching classes to join the Antiwarmist cause.

  22. 22
    R. Gates says:

    What is the general opinion about papers such as this one that would seem to show a tight connection between GCR’s and climate fluctuations:

    Asked in a different way: Without the strong correspondence between solar cycles, GCR’s and cloud cover, can decreases in total solar irradiance alone be enough to explain the cooler temps of the Little Ice Age?

    [Response: I think some of the claims seem a bit far-fetched. We know there are many factors that can affect our climate, such as orbital variations, shifts in geographical features, volcanos, GHGs, etc. But I guess more research will throw more light on the issue. -rasmus]

  23. 23
    James Allan says:

    The overblown press release strikes yet again. It makes you wonder what was in the submitted version of the paper that subsequently got toned down…

  24. 24
    LazyTeenager says:

    When I first came across the abstract for this paper I was uncomfortable with it because I could not see how it got published since it does not satisfy the novelty criteria in the light of all the work around ion clusters in the literature going back to cloud chambers to detect particle tracks.

    I purchased the paper and had a look. General conclusions are:
    1. The experimental section does not explain enough about the measurement techniques so there is no way to assess the reliability of their measurements.
    2. There are too many loose ends.
    E.g. The aerosols are not characterized apart from size.
    The supposed H2SO4 concentration is 10 times normal
    Their own modelling suggests that under some conditions not studied, the correlation is negative not positive.

    Altogether the hyped conclusions related to the supposed application of this work to cloud formation are bogus and have little relationship to the uncertainties latent in the research.

  25. 25
    Jeff Jones says:

    Solar irrafiance alone does not appear to signifcant to have cause the LIA. The correlation between sunspots, GCRs, volcanoes (possibly), and aerosols probably is.

  26. 26
    Pete Dunkelberg says:

    R. Gates @ 22, see various posts here at RC (keyword Svensmark) on the lack of any significant correlation of cosmic rays with climate forcing.
    The paper you linked almost dismisses orbital forcing (Milankovitch cycles). There are three components to orbital changes and sorting their effects is not trivial nor completely clear, but dismissal is uncalled for. See Tamino for a discussion of recent papers.

    So, “…can decreases in total solar irradiance alone be enough to explain the cooler temps of the Little Ice Age?” No, but it’s not supposed to. See this 1979 paper by Robock. There must be some recent papers on this.

  27. 27
    R. Gates says:

    I do not doubt the high probability of of anthropogenic factors in current climate change, but I think the CLOUD experiment of Jasper Kirkby at CERN is most interesting and the correspondences he has outlined between climate fluctuations over longer periods and GCR’s certainly can’t be easily dismissed. Also, in watching several presentations and reading several papers by Kirkby, I never found him dismissing Milankovitch forcings at all, but rather outlining how the GCR/cloud modulation link could fit nicely into other missing pieces of the climate puzzle.

  28. 28
    Prokaryotes says:

    More recent news about clouds…

    “Bacteria often leave their hosts feeling under the weather. And even when the hosts are high-altitude parcels of air, microbes can be a source of inclement conditions, a Montana research team finds. Cloudborne bacteria might even pose climate threats by boosting the production of a greenhouse gas, another team proposes.

    Both groups reported their findings May 24 at the American Society for Microbiology meeting in New Orleans.

    These data add to a growing body of evidence that biological organisms are affecting clouds”

  29. 29
    chris says:

    R. Gates @ 22

    ”Without the strong correspondence between solar cycles, GCR’s and cloud cover, can decreases in total solar irradiance alone be enough to explain the cooler temps of the Little Ice Age?”

    What “strong correspondence between solar cycles, GCR’s and cloud cover”?!

    The Kirkby review you link to is poor. Focussing on the Little Ice Age (LIA) Kirkby completely misrepresents scientific knowledge to insinuate a role for GCR’s in temperature change from the LIA (Maunder minimum) and the mid 20th century. Kirkby asserts (see page 6 of the review you urled):

    “The increase in irradiance amounts to less than 0.5 W/m^2, which corresponds to about 0.08 W/m^2 at the top of the atmosphere, globally averaged (Fig. 5). Assuming a climate sensitivity of 0.7 K/W/m^2, this would contribute less than 0.06C of the estimated 0.6 C mean global warming between the Maunder Minimum and the middle of last century, before significant anthropogenic contributions could be involved.”

    But Kirkby’s Figure 5 and its discussion is simply incorrect. His reference to Lean et al (2002) (his ref [6]) is to a paper in which Judith Lean only analyzes solar irradiance back to 1840. The data shown is actually from a 2005 paper [Y.-M. Wang, J. L. Lean and N. R. Sheeley, Jr. Modeling the Sun’s Magnetic Field and Irradiance since 1713 Astrophysical J. 625 522-538]. In that paper Lean determined that the increase in solar cycle-averaged irradiance is 1-1.4 W/m2. This corresponds to a temperature rise of 0.14 oC- 0.2 oC (not “less than 0.06 oC”!).

    And Kirkby pretends that there was no significant contribution from the anthropogenic rise in [CO2] when it’s well known that [CO2] rose from around 280 ppm (pre-industrial) to 300 ppm by 1900 to 310 ppm by 1940. Using the middle of the range of climate sensitivities of 3 oC of warming at equilibrium per doubling of [CO2], a rise of [CO2] from 280-310 ppm should give 0.44 oC at equilibrium. We might expect to have realized 0.3 oC of that by 1950. So it’s completely straightforward to account for pretty much all the warming from the Maunder minimum to mid 20th century by forcings we expect to exist. Not to mention the volcanic contribution that likely suppressed LIA temperatures a tad – Kirkby ignores this too.

    Rather typically of his review Kirkby insinuates a role for GCR’s, in this case by blatantly misrepresenting Lean’s solar iradiance reconstructions and pretending we don’t know what we do know very well; that there was certainly a significant contribution from anthropogenic [CO2].

    Note also that there’s no evidence for a role for GCR’s on MWP temperatures; Kirkby’s figure 2 indicates that these don’t correlate at all – the MWP warming leads the rise on GCR’s by 50-100 years. Likewise the Shaviv and Veizer analysis described in Kirkby’s figure 11 has been pretty much completely discounted, amongst others by Veizer himself.

  30. 30
    R. Gates says:

    Chris @ #29:

    Thanks for the insightful reply. To a non-scientist such as my self, the Kirkby paper would appear to present the smoking gun to many climate puzzles, and of course I’m sure he’d like his CLOUD experiment to be the light that shines on many of the unanswered climate puzzles. I know he’s got a major paper coming out very soon on all this and we’re bound to have some interesting discussions about it.

  31. 31
    Brian Cairns says:



    While I totally agree with the overall message of this post, I think that your stated CCN size is too high. There are very few 10 micron particles around and typical CCN sizes in the real atmosphere are 200-500 nm.

    [Response: Right, but they need to grow ~ 10 micron to form cloud droplets. The process, as you indicate, is complex, involving more than one phase, such as the condensation of water vapour. -rasmus]

    A significant fraction of CCN can be smaller than 0.1µm in radius and the variability and sources of particles of this size are a primary issue in the indirect effects of clouds on climate. Cloud droplets over land are generally less than 10 µm in size, more typically 5-7 µm. So, please do not make dogmatic statements about things that you do not know about and moreover are misleading.

  32. 32
    Septic Matthew says:

    An incremental step blown up

    Just so.

  33. 33
    Pete Dunkelberg says:

    Jeeze Brian, if you would just give a reference to peer reviewed data, or explain some physical processes, you would make a much better impression than you make by name-calling.

  34. 34
    Keith Dow says:

    On a nit picky note, GCR generally refers to cosmic rays that originate in our own galaxy.

  35. 35
    R. Gates says:

    On a related note: Does anyone here know where the best source would be for getting a detailed chart of Be-10 concentrations from ice cores plotted against global temps during the past 10,000 years? Seems like this should be readily available but the few I’ve seen are poor quality and even contradict each other.

  36. 36

    Rasmus notes that other factors besides ionization seemed at least as important in influencing the nucleation rate. This was also the case during the first round of CERN experiments, where a very minor temperature increase (of 0.1 degree) was often more effective at increasing the nucleation rate than bumping up the ionization rate. ( )

    As Rasmus also mentioned, ions play a role in atmospheric nucleation, but this role is not as important as some make it out to be.

    Minor correction (echoing Erik #1): clouds need particles of the size approximately a few nundred nanometers to form cloud drops, which are around 10 micrometer in diameter. See also

  37. 37

    #31 Brian Cairns

    I’m with Pete on this one. Can you back up what you are stating so absolutely? More specifically, can you show peer reviewed work that has survived peer response that backs up your claims? I’m no expert so I can only judge things that have been through the peer review milling process and the quality of the grain that comes out the other side and makes it to market.

  38. 38
    veritas36 says:

    Well, there sure are a lot more clouds over my head, and skies that are whitish rather than vivid blue, so I’m relieved to learn that it’s due to thing-a-ma-bobbies from outer space.

  39. 39

    #31 Brian Cairns

    You have made a dogmatic statement and claim Rasmus does not know what he is talking about. I would like to understand why? Are you going to explain it or is this just a hit and run?

    What significance does your statement have and in what context, and based on what evidence. Did that evidence survive peer response? I really do want to know. Quite frankly, because I’m not an expert, when we are talking about µm particle in the atmoshpere, I don’t believe anything until I can see the big picture, and that big picture is well founded.

    Can you provide relevant context, or not in the context of the subject of the article, which is the paper mentioned above ?

    The paper:

    The now conventional view on global warming, as stated by the Intergovernmental Panel on Climate Change, is that most of the warming recorded in the past 50 years has been caused by emissions of manmade greenhouse gases. But some scientists argue that the Sun might have a significant influence on changes to the Earth’s climate, pointing out that in centuries past there has been a close correlation between global temperatures and solar activity.

    However, changes to the Sun’s brightness are believed to have altered temperatures on Earth by no more than a few hundredths of a degree in the last 150 years. Researchers have therefore been investigating ways that the Sun could indirectly modify the Earth’s climate, and one hypothesis, put forward by Henrik Svensmark of the National Space Institute in Copenhagen, posits a link between solar activity and cosmic-ray flux.

    The press release:

    researchers say this is the best experimental evidence yet that the Sun influences the climate by altering the intensity of the cosmic-ray flux reaching the Earth’s surface.

    So that is our context and how these statements can be used to confuse others about the significance of GCR’s regarding our current global warming event. Your statement does not address the subject though, so what significance does it have in the bigger picture? Recall of course there has been no significant trend in GCR’s that could account for the connections being touted by weak inference. So what are you really saying?

    Specifically, do you believe current global warming is caused by GCR’s and thereby greenhouse gases are unimportant? Or are you simply saying there are lot’s of 5-7 µm particles and not offering context?

  40. 40
    Marco says:

    People might be interested to know that Knud Lassen, who first (IIRC) published about the GCR-climate idea, has turned 90 today, and thought it relevant to note that “Den globale opvarmning skyldes med stor sandsynlighed den menneskeskabte forøgelse af Jordens naturlige drivhuseffekt” (see , unfortunately in Danish only).

    To translate: “the global warming is with a large likelihood due to the human-caused increase of the earth’s natural greenhouse effect”.

    Not the best translation, but I guess it is clear enough.

  41. 41
    Tom W. says:

    #30 R. Gates

    You can look at

    They have all kinds of data on lots of ice cores. The search function is quite what it used to be though. I would limit your search to Antarctica and Greenland and look for GRIP, GISP2, Dome Fuji, South Pole and Dronning Maud Land. There are several others with long Be10 records. I wouldn’t say that they are poor quality per se, Be-10 measurements themselves are only good to about 2-3% at the very best and this doesn’t include uncertainties due to local weather. Also if you run a few hundred samples a few are going to be >3sigma outliers by chance and certainly a mistake or two may have crept in.

    Also there are two different datasets that may be reported – concentration (atoms/g) and flux(atoms/cm^2/yr) and these are not directly comparable, you have to be careful comparing low and high accumulation rate sites.

    Although Be10 records do not show great correlation below the decadal scale (but they will show the 11 year cycle if taken at annual resolution) they start to show much better agreement at 30+ yr timescales and in identifying large events.

    Good hunting

  42. 42
    CM says:

    Marco #40,

    So, it’s a double anniversary — Lassen is 90 (happy birthday), and the solar-GCR-climate hypothesis turns 20 this year? Sounds like a good time to take stock.

    Very telling graphic in that article, though I’m a bit confused as to how they measure the solar cycle in degrees C…

  43. 43
    Marco says:

    CM, the graphic comes from a paper by Lassen, and IIRC the solar cycle was scaled to degrees Celsius under the assumption that the temperature was fully correlated with the solar cycle. Just to indicate that the current warming could not be due to the solar cycle.

  44. 44
    Michael Doliner says:

    I don’t know where to put this so I will try here. Climate science is obviously complicated with many feedback mechanisms, but it seems to me that the increase in greenhouse gases should mean that more heat is trapped every year than escapes. The only exceptions might be exceptional years, like those containing volcanic activity. Since more heat is trapped the average temperature should go up unless that heat is used in some way other than to increase temperature. Ice melting and water evaporation seem to be the only candidates. Therefore a statistic that combines average global temperature, global humidity, and the negative of ice cover should increase every year. Are these other measurements possible? Did I miss something?

  45. 45
  46. 46
    Brian Dodge says:

    “Quite frankly, because I’m not an expert, when we are talking about µm particle in the atmoshpere, I don’t believe anything until I can see the big picture, and that big picture is well founded.”

    John P. Reisman (OSS Foundation) 31 May 2011 at 2:41 AM

    A big picture of cloud droplet size may be seen at

    “…the smallest CDR[cloud droplet radius] values are found over regions of high aerosol index, and the largest values are over the open oceans where the atmosphere is very clean: CDR is between 6 and 10 μm over land surfaces, values over the oceans vary between 12 and 14 μm in remote areas down to the same low values of 6 μm in regions with the highest aerosol index.

    From –
    Science 1 February 2002: Vol. 295 no. 5556 pp. 834-838 DOI: 10.1126/science.1066434

    Aerosol Effect on Cloud Droplet Size Monitored from Satellite

    1. Francois-Marie Bréon,
    2. Didier Tanré, and
    3. Sylvia Generoso1

  47. 47
    Brian Cairns says:

    A paper discussing the difficulty of getting from nm sized nucleation mode to a size that can generate cloud particles is:
    Erupe, M. E., et al. (2010), Correlation of aerosol nucleation rate with sulfuric acid and ammonia in Kent, Ohio: An atmospheric observation, J. Geophys. Res., 115, D23216, doi:10.1029/2010JD013942.

    Regarding peer reviewed literature that states what size particles need to be to form cloud droplets and what is important for the formation of cloud drops a well regarded recent paper is:
    Dusek U., Frank G. P., Hildebrandt L., Curtius J., Schneider J., Walter S., Chand D., Drewnick F., Hings S., Jung D., Borrmann S., and Andreae M. O.: Size matters more than chemistry for cloud nucleating ability of aerosol particles, Science, 312, 1375-1378, 2006.
    Figure 2 shows the importance of particles with radii smaller than 0.1 µm

    A comprehensive survey of low level cloud droplet sizes which shows droplet sizes are for these clouds are generally between 5 and 15 µm is:
    Miles, Natasha L., Johannes Verlinde, Eugene E. Clothiaux, 2000: Cloud Droplet Size Distributions in Low-Level Stratiform Clouds. J. Atmos. Sci., 57, 295–311. doi: 10.1175/1520-0469(2000)0572.0.CO;2

  48. 48

    #46 Brian Dodge

    Thanks Brian, but that is still not the big picture I am referring to. I would need to assimilate a lot more of the mechanisms that are substantial and the general science in the field. Thus far I can only claim a superficial review and I do not satisfactorily understand the underlying mechanisms as yet.

    The sizes and lifetimes may and/or may not, depending on circumstance (component/mechanism), relate to the impact potential on warming, or cooling, or degrees of neutrality. How significant is the impact potential on forcing over time? How significant is the relationship when placed in the context of current physics and forcing potentials regarding total radiative forcing and albedo… and different aerosols, impacts and lifetimes in the atmosphere in relation to the lifetime of clouds and various stages of CCN development?

    In general, since clouds have relatively short lifetimes and aerosols have relatively shorter/longer lifetimes (dependent), and GHG’s have long lifetimes years to centuries, what is the significance of one in relation to the other on total impact potentials and implications for warming and cooling? Those are the relationships that seem critical when we are discussing global warming man-made or GCR.

    I’m not deep enough in the subject to feel comfortable with conclusions on my own. I trust peer review and peer response to the extent they can provide a basis for understanding, confidence and conclusion to the degrees possible though. Verification is the rule, as possible.

    Having read other material on the consequences and relationships of CCN’s and lifetimes regarding papers that have been written, it seems that a lot of the papers coming from the Svensmark angle, so to speak, are not conclusive enough of definitive impact in the impact potentials for global warming, to jsutify the claims made by Svensmark, or the press about his, or similar, work. Svensmark and the press often reach beyond the substance of the work itself to make cliams not supported by the work. I find this scientifically misleading, if not dishonest.

    My questions now lead toward the processes involved in development of CCN’s based on particle, particle size, and related interactions with relevant mechanisms, that lead to ‘significant’ changes in relation to clouds that can be sufficiently quantified so as to determine global warming impacts.

    So, from my lack of understanding here, I think the question revolves around ‘significance’, of the total mechanisms in relation to potential to alter radiative forcing and enhancing the greenhouse effect. And of course, do GCR’s play a roll and how much? So far in relation to other identified mechanisms that are quantified, GCR’s don’t seem to play a big roll in current changes… or past for that matter i.e. Laschamp Anomaly.

  49. 49

    #47 Brian Cairns

    Thank you, I have some reviewing to do, but first coffee :)

  50. 50

    #47 Brian Cairns

    Upon review of the material referenced and your general comment in #31 I am led to believe that it seems a misunderstanding. Rasmus did recognize the different particle sizes from 4nm to 10 micron. While the mechanisms are still quite mysterious it is clear there is an abundance of particles smaller than 10 microns but Rasmus never stated otherwise. He merely pointed out there is a growth process involved. So it seems there is no actual debate here.

    Interesting papers though and thank you for the references. It seems that, while a mystery, one can still have some fun hypothesizing. I get the notion that the mechanism seems to require or favor a particular environment such as spring or fall for particular formation capacity and interestingly the idea of snowballs come to mind.

    Maybe the process of ‘size matters’ fits with an analogy of a snowball running down a hill? As the size grows, the potential for growth may then increase? Possibly due to surface properties, or sheer mass giving way to potential to bump into things more? Or might there be a charge or magnetic principle involved. This is truly a challenging and interesting area and I still don’t have a clue :)