Yet another trick of cosmic rays

Climate Change: News and Comments

In the climax to the Danes’ experiments, cloud seeds flout the theories

Near to the end of the story that starts with stars exploding in the Galaxy and ends with extra clouds gathering, a small but important paragraph was missing till now. From experiments in Copenhagen reported in 2006 and reconfirmed in 2011 in Aarhus and Geneva (CERN, CLOUD), cosmic rays coming from old supernovas can indeed make molecular clusters a few millionths of a millimetre wide, floating in the air. But can these aerosols really grow nearly a million times in mass to be large enough to become “cloud condensation nuclei” on which water droplets can form – as required by Henrik Svensmark’s cosmic theory of climate change?

Opponents pointed out that theoretical models said No, the growth of additional aerosols would be blocked by a resulting shortage of condensable gases like sulphuric acid in the atmosphere.

Not for the first time, an unexpected trick that Mother Nature had up her sleeve is revealed by experiment. The discovery is elegantly explained by a new way in which sulphuric acid forms in the atmosphere, as announced in a paper by Svensmark and two of his colleagues in Denmark’s National Space Institute in Copenhagen, Martin Enghoff and Jens Olaf Pepke Pedersen. They have submitted it to Physical Review Letters. A preprint is available on arXiv here

Svensmark, Enghoff and Pepke Pedersen

A brief history. Last year’s attempts to dismiss the Aarhus and CERN results as inconsequential for climate change didn’t dismay the Danes. They knew there was something wrong with the current understanding because they had observational support for the whole chain from solar activity to cosmic rays to aerosols to clouds in the real atmosphere (Svensmark, Bondo and Svensmark 2009). In order to dig into the physics, they decided to rebuild, in the basement of the Space Institute, the 8 cubic metre experimental chamber SKYII which six years ago was used as the CLOUD prototype chamber at CERN,

In the limelight of the atmospheric drama, sulphuric acid is one of the commonest of trace gases and very important for both the formation and the growth of aerosols. When the Sun rises in the morning, its ultraviolet rays convert sulphur dioxide, ozone and water vapour in the air into sulphuric acid molecules. These are continuously lost as they club together with further water and a little ammonia into very small molecular clusters. Nevertheless, the concentration of sulphuric acid rises to a peak and then diminishes as the Sun goes down in the evening.

A clue that something more is going on comes from the persistence all through the night of sulphuric acid at about 10 per cent of the daytime maximum. If these molecules too are continuously lost, they must be replenished by a chemical reaction that doesn’t need ultraviolet light.

What did the new experiment called SKY2 show? Without going into technical details that you’ll find in the paper, let’s just say that the primary result flatly contradicts the theoretical prediction that the infant aerosols couldn’t grow up into cloud condensation nuclei. Here’s a figure from the paper.

Molecular clusters grow over time, in the SKY2 experiment in Copenhagen. The horizontal axis is scaled in nanometres (millionths of a millimetre) and each blue point shows the relative number of clusters of that size before and after the experimental runs. Anything over 1.0 means that growth has continued. In contrast, the red points illustrate a pessimistic prediction of previous theories, that growth should cease when the size passes 50 nanometres. On the other hand, the black curve running through the blue points shows what is to be expected if there is a continual supply of sulphuric acid. The persistent growth of clusters occurs only in the presence of gamma rays that simulate cosmic rays and set electrons free to influence the chemistry.

So what’s the explanation? What new pathway supplies the sulphuric acid needed to keep the growth going? The Danes recall a suggestion in their 2006 SKY report that electrons can act like catalysts, being used over and over again to promote chemical action. In the new paper they say: A possible explanation could be that the charged clusters are producing additional [sulphuric acid] molecules from reactions involving negative ion chemistry of [ozone, sulphur dioxide and water], where a negative ion can be reused in a catalytic production of several [sulphuric acid molecules].

Depending on the concentrations of trace gases, several may mean dozens. And where do the electrons come from? They are liberated by cosmic rays raining down by night as well as by day. If the results of the experiment and these ideas are confirmed, there’s an amazing pay-off. The cosmic rays help to make the extra sulphuric acid that allows (1) a number of additional aerosols to form and (2) a larger number of aerosols to grow into cloud condensation nuclei. Without this second effect the aerosols would grow slowly and most of the extra aerosols would be lost before becoming large enough to seed clouds.

That ions liberated by cosmic rays promote a second pathway for forming sulphuric acid was already known from an experiment performed in Copenhagen in a collaboration with the University of Copenhagen and the Technical University of Tokyo (see the Enghoff et al. reference below). Depending on whether the sulphuric acid comes from ultraviolet action or is ion-induced, it has different signatures in the relative abundances of isotopes of sulphur. What’s more, the number of molecules made by the ion route greatly surpassed the number of ions available, again implying reuse of the electrons in a catalytic fashion.

To summarize the latest paper, the Svensmark, Enghoff and Pepke Pedersen abstract reads:

In experiments where ultraviolet light produces aerosols from trace amounts of ozone, sulphur dioxide, and water vapour, the number of additional small particles produced by ionization by gamma sources all grow up to diameters larger than 50 nm, appropriate for cloud condensation nuclei. This result contradicts both ion-free control experiments and also theoretical models that predict a decline in the response of larger particles due to an insufficiency of condensable gases (which leads to slower growth) and to larger losses by coagulation between the particles. This unpredicted experimental finding points to a process not included in current theoretical models, possibly an ion-induced formation of sulphuric acid in small clusters.

Scandals of a political character engulf climate physics these days, but future historians may shake their heads more sadly over scientific negligence. Isn’t it amazing that such a fundamental activity of sulphuric acid, going on over your head right now, has passed unnoticed since 1875 when cloud seeding was discovered, since 1996 when Svensmark found the link between cosmic rays and cloud cover, and since 2006 when the Danes suggested the catalytic role of electrons? Perhaps the experts were confused by the ever-present dislike of the role of the Sun in climate change.

So Svensmark and the small team in Copenhagen have had nearly all of the breakthroughs to themselves. And the chain of experimental and observational evidence is now much more secure:

Supernova remnants cosmic rays solar modulation of cosmic rays variations in cluster and sulphuric acid production variation in cloud condensation nuclei variation in low cloud formation variation in climate.

Svensmark won’t comment publicly on the new paper until it’s accepted for publication. But I can report that, in conversation, he sounds like a man who has reached the end of a very long trek in defiance of continual opposition and mockery.


Henrik Svensmark, Martin B. Enghoff and Jens Olaf Pepke Pedersen, “Response of Cloud Condensation Nuclei (> 50 nm) to changes in ion-nucleation”, submitted for publication 2012. Preprint available at

H. Svensmark, T. Bondo and J. Svensmark, “Cosmic ray decreases affect atmospheric aerosols and clouds”, Geophysical Research Letters, 36, L15101, 2009

Henrik Svensmark, Jens Olaf Pepke Pedersen, Nigel Marsh, Martin Enghoff and Ulrik Uggerhøj, ‘Experimental Evidence for the Role of Ions in Particle Nucleation under Atmospheric Conditions’, Proceedings of the Royal Society A, Vol. 463, pp. 385–96, 2007 (online release 2006). This was the original SKY experiment in a basement in Copenhagen.

M. B. Enghoff, N. Bork, S. Hattori, C. Meusinger, M. Nakagawa, J. O. P. Pedersen, S. Danielache, Y. Ueno, M. S. Johnson, N. Yoshida, and H. Svensmark, “An isotope view on ionising radiation as a source of sulphuric acid”, Atmos. Chem. Phys. Discuss., 12, 5039–5064, 2012. See

Some relevant items on this blog

Aarhus experiment

CERN CLOUD experiment

Observational evidence of aerosol growth

Summary of Svensmark’s theory


27 Responses to Yet another trick of cosmic rays

  1. cogdissonancedagain says:

    “No chance of a real* Nobel this time round I s’pose”?

    “You idiot; wot are you smoking”!, was the stern reply

    * science, not that peace rubbish

  2. Bengt A says:

    Very, very nice paper! Svensmark and his team should be proud if themselves.

    Is it possible, in your opinion, to quantify the solar contribution to the 20th century warming on the basis of this paper?

  3. Mike says:

    Thanks for trying to keep the scientific community honest Nigel.

    Why does it feel like we realists are trying to push scat up hill with a sharp stick?

    It seems to me that there will be many extremely red faces among the Warmist Deniers before too much longer. Another 5 years of cold winters and even reducing temps should do it.
    Not to mention a falling sea level!

  4. matthu says:

    Thank you once again for being one of the very first sites to bring us exciting news of what Svensmark is up to!

  5. […] Read on at Calder’s Updates Share this:PrintEmailMoreStumbleUponTwitterFacebookDiggRedditLike this:LikeBe the first to like this post. This entry was posted in Climate Change and tagged cloud nucleation, cosmic rays, svensmark. Bookmark the permalink. ← Green Stimulus Spending: A Litany of Failure […]

  6. Reblogged this on contrary2belief and commented:
    New discoveries about the acid skies.

    Cosmic rays may provide energy to form sulphuric acid molecules that provide cloud nucleation sites; supplementing those produced by the sun’s UV light in the daytime.

  7. Russell Seitz says:

    Unpublished, unquantified, and considering the small cosmic ray flux and its even smaller deltas thoroughly underwhelming.

    I’m afraid Nigel’s search for straws to popularize is looking increasingly cranky.

  8. Mike W says:

    “I’m afraid Nigel’s search for straws to popularize is looking increasingly cranky.”

    On The $CAGW$ payroll perhaps.? 🙂
    A when its published you will change your mind..of course not .
    $CAGW$ is not falsifiable…it has something for every “useful idiot”.

  9. Andrew McRae says:

    Mr Calder I congratulate you on the glowing reference you received in Dr Svensmark’s latest paper. (1202.5156v1)

    On the plus side, cosmic rays are mostly 10^9 eV. Cs137 decays with product energies of less than 10^6 eV, so if a cloud seeding effect can be demonstrated with less powerful radiation than in nature then it must surely be happening in nature.

    However I must regrettably express some reservations about the new paper. I am not trying to make any accusations here; we either use the scientific method uniformly or else we have nothing to push back the dark.

    Question 1 : The majority of cosmic rays are protons and Alpha particles and only 1% are Beta decay particles. Cs137 decays mainly into Beta particles followed by a secondary gamma decay of equal intensity. So what Svensmark used is mostly not the same type of particles as cosmic rays. Does that matter? Does it show that only 1% of cosmic rays are making all the cloud cover changes? I don’t know, but the paper should have said something about this.

    Question 2 : The level of radiation entering the chamber is not tracked or calibrated, which seems a rather bizarre oversight when it is the critical parameter of the mechanism he is trying to examine! How much of the radiation source penetrates the stainless steel walls? Is it sufficient to assume it’s close to 60MBq of 0.6 MeV gamma rays? Why must we assume? He should have measured this, at least once at the beginning.

    Rather than try to hassle the good doctor directly, I wondered if you might be familiar enough with the physics of the experiment to shed some light on the above questions?

    Perhaps there is an easy answer here which just isn’t obvious to me as an amateur.

    • Bengt A says:

      Svensmark and colleagues showed last year that in an experiment like this a particle beam is exchangeable with gamma rays. The ionization effect on air is similar (you’ll find that paper here).

      It is of little importance whether they use 50 or 60 MBq. The set up is somewhat simple but the only thing they need to care about is that the addition of gamma rays is stepwise and held constant. Then they closely monitor how that stepwise change in ionizations propagates into aerosols that grow larger and larger.

      One ingenious thing about this experiment is the simple and cost effective setup. They have exchanged an expensive and bulky particle accelerator with Cesium 137, a radioactive source that you will find in most every science classroom. That is why they beat CLOUD to this result. I imagine we will eventually see something similar reported from the CLOUD-experiment.

    • calderup says:

      I’m afraid you’re way off, Andrew. The natural cosmic rays don’t come from Cs137 but from natural accelerators in supernova remnants. The primary protons and alpha particles are replaced low in the atmosphere by secondary particles – primarily muons. These liberate the electrons from molecules in the air.
      In the experiment, gamma rays perform the same role, and the direct emission of beta particles is irrelevant. As for measuring the ionization, of course they did.

  10. […] Supernova remnants → cosmic rays → solar modulation of cosmic rays → variations in cluster and sulphuric acid production → variation in cloud condensation nuclei → variation in low cloud formation → variation in climate.” From: […]

  11. Adam says:

    Nigel Calder, I’d be interested to know your opinion on these two papers, which claim to refute the arguments made in Svensmark’s 2009 paper

    Click to access 2009GL040961.pdf

    Click to access acpd-9-21525-2009.pdf

    • calderup says:

      I know these papers, Adam, but life’s too short to reply in detail to all the attempts to nibble away at bits of Svensmark’s story. Consider this: although journals don’t usually care to go on publishing negative results, they make an exception for the dozens of attempts to falsify Svensmark. Remember Einstein’s comment on the pamphlet Hundert Autoren gegen Einstein (1931) – “If I were wrong, one would be enough”.

  12. Alex Harvey says:


    I posted this at Lubos Motl’s blog and Lubos suggested I repost here.

    Back in August, Gavin Schmidt claimed that in order for the Svensmark theory to explain recent global warming, the following four points would need to be established:

    “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.”

    Now 4 looks like something that is already well-established; maybe 3 is established too? Points 1 & 2 on the other hand look like more serious objections. They also claim an observation of decreasing trend in cosmic rays would be needed, although I recall reading at Nigel’s blog about this too.

    Am I right that this new paper claims to have demonstrated points 1 & 2? Sorry, I am a bit confused by the meaning of Gavin’s points. Any general comments on how this experiment relates to RealClimate’s comments?

  13. […] studio, del quale abbiamo avuto notizia dal blog di Nigel Calder, è disponibile in pre-print su Arxiv, sebbene debba ancora essere accettato dalla rivista cui è […]

  14. dahuang says:

    Hi Nigel, how is the peer-review process going for this paper? The manuscript was received by PRL in last December and more than four months have passed now. Has it been rejected or under revision?

  15. […] In contrast, there is a great deal of evidence for a solar-magnetic driver of climate (second section here). This is the real alternate hypothesis, and there is at least one well developed theory for how it could occur: Henrik Svensmark’s GCR-cloud. […]

  16. jonmuench says:

    Reblogged this on jonmuench and commented:
    This needs to be at the forefront of scientific discussion before the jury goes home on Climate Change

  17. simon w says:

    the data from ice cores has long shown a correlation between climate change and solar activity. the planet has warmed and cooled periodically long before mans mass burning off carbon based fuels. it seems that this behaviour’s coincidence with the warming period we have had for the last 400 years or so is all that the man made climate change gang has to support their theory. he again we have more evidence of a solar affected climate change that is been refuted to protect the jobs and industry that has built up around the whole subject. it seems as if never a day goes by where i see empirical science been ignored because it doesn’t fit some others theory. can we please return to a honest use of the scientific method where theory is the starting point of research and not the finish.

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