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

Sorting out the Svensmarks Junior



Jacob, Joachim and Julius

A key paper on the effect of solar eruptions on atmospheric aerosols and clouds, published in 2009, is referenced as H. Svensmark, T. Bondo and J. Svensmark, Geophys. Res. Lett., Vol. 36, L15101, 2009. See last year’s blog post here

Jacob Svensmark

H is for Henrik, T is for Torsten, and J is for Jacob. It’s not hard to work out that Jacob Svensmark is Henrik’s son. He’s reading physics at the Technical University of Denmark (DTU). During the past few years Jacob has helped his father with complex computations of the behaviour of cosmic rays in the heliosphere, and he also took part in the CLOUD Prototype experiment at CERN in 2006. Busy stuff, on top of his own university studies.

But the names of Henrik’s other sons also begin with J, so casual googling could mix them up. While Henrik and Jacob are both polymaths in science, the Svensmark talents head in quite different directions with Joachim and Julius.

Joachim Svensmark

Joachim is a remarkable guitarist, and you can see and hear him here I’m pleased to report that his instrument is a Fender that Henrik bought for Joachim during a visit for scientific chats in my home town of Crawley, England. Henrik modified the guitar with different pickups and a preamplifier in the body.

It has a sound Joachim likes,” Henrik assured me. “His way of playing requires very strong string bending and he wears the frets down very fast. Using thin strings is not an option since he thinks it gives a thin sound.” Here’s more music from Joachim but the word is that, after plenty of very popular gigs, he is resuming his high-school studies in earnest.

Not to be outdone, as the youngest of these junior Svensmarks, Julius follows a sporting route and plays in Denmark’s Under-21 Volleyball Team. They beat Romania last month, which was something of a sensation.

Julius Svensmark is No. 14 in the Under-21 Team

Sprites fight


Pick of the pics and Climate Change: News and Comments

Sprites fight in the upper atmosphere

Two enormous electrical discharges called sprites are seen brushing together in this conflation of a series of high-speed TV images, looking out over the sea from Catalonia towards Italy. The scale shows the heights above sea level, with the whole phenomenon stretching from 50 to 83 km altitude, and all over in a matter of milliseconds. Source: Joan Montanyà et al., see references.

The following video is in Spanish, but it includes the event shown as a still image above, fully animated.

You can see other video examples of high-altitude  phenomena called sprites, elves and jets in the first image on this ESA page

Sprites, elves and jets link thunderstorms and the upper atmosphere, as in this diagram from the National Space Institute in the Technical University of Denmark (DTU).

If “elve” (not “elf”) bothers you in the diagram, be aware that elves is a joky acronym: “emissions of light and VLF perturbations from electromagnetic sources”.

The European Space Agency is preparing an experiment called the Atmosphere-Space Interactions Monitor (ASIM) to observe these events from the International Space Station. The word is that it’s due to fly in 2013.

As for the link to climate physics, here’s a comment made by the ASIM principal investigator a few years ago:

“The question is how are these giant flashes of lightning created and how often do they take place”, says senior scientist Torben Neubert, head of the project at the Danish National Space Centre.

It may well be that the large electrical bursts remove ozone from the atmosphere, and in so doing influence the climate. “We need to understand the natural processes which influence the atmosphere and this can help us decide which changes in the climate are man-made”, Torben Neubert states.

It’s hard to resist pointing out a moral in this tale. Seafarers and mountain-dwellers have noticed these high-altitude lightning flashes for centuries or millennia. They may have provoked some religious experiences. Back in 1925 C.T.R. Wilson, who invented the cloud chamber, predicted the creation of very energetic “runaway” electrons by thunderstorms. In 1956, at the age of 87, Wilson at last saw the high-altitude phenomenon for himself. So did airline pilots and UFO watchers.

Yet our know-it-all meteorologists scorned the existence of sprites until 1990, when 74-year-old John Winckler from the University of Minnesota reported that he had caught a brief image with a low-light TV camera that he was testing. So what else don’t we know, or what are we ignoring, about events and processes at the Earth’s frontier with outer space?

For an impression of how lively this field of research now is, see the titles in


J. Montanyà et al.,”Intensified high-speed video recordings of sprites and elves over the western Mediterranean Sea during winter thunderstorms.” Journal of Geophysical Research 115, A00E18, 8 PP., 2010

Press releases are available in English

and in Spanish

Neubert quote from

C. T. R. Wilson, “The acceleration of Beta-particles in strong electric fields such as those of thunderclouds”, Proc. Camb. Philos. Soc., 22, 534, 1925

J.R. Winckler et al., “Television image of a large upward electrical discharge above a thunderstorm”, Science, 249, 48-51, 1990.

About Henrik Svensmark


About Henrik Svensmark, climate physicist

National Space Institute, Technical University of Denmark

Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark.

Phone (+45) 3532 5741, e-mail:

DTU Sun-Climate website

Prof. Henrik Svensmark leads the Center for Sun-Climate Research at the National Space Institute in the Technical University of Denmark (DTU). He previously held research positions at the University of California Berkeley, the Nordic Institute of Theoretical Physics, the Niels Bohr Institute and the Danish Meteorological Institute. He has published more than 50 scientific papers on theoretical and experimental physics, including a succession of landmark papers on climate physics.

Svensmark received the Knud Højgaard Anniversary Research Prize in 1997 and the Energy-E2 Research Prize in 2001. Read the rest of this entry »


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