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Henrik Svensmark: The Cosmic-Ray/Cloud Seeding Hypothesis Is Converging With Reality

Dr Henrik Svensmark of the Danish National Space Centre in Copenhagen has pioneered the study of the effects of cosmic rays on cloud formation. The GWPF put a series of questions to him concerning the recent results from CERN’s CLOUD experiment.

How significant are the CERN results?

I welcome the CLOUD results. They basically confirm our own experimental results since 2006, and does so within a larger variation of parameters. It seems to say that ions are fundamental for the nucleation of new aerosols.

Some in the media have said that the fact that CERN’s produced clusters that were too small spells the demise of the cosmic ray-cloud theory. What is your reaction?

Our group has closely studied the effect of cosmic rays on cloud formation, e.g. in our 2009 paper. Here the obvious question is what the implications are for clouds and the Earth’s clouds and radiative balance, which is indirectly posed at the end of the CLOUD paper, when it wonders what fraction of the small aerosols grow to cloud-seeding size.

This was also the question we asked following our own experiments. It turns out that this question can be answered with what one can call “natural experiments” where solar explosions (Coronal Mass Ejections) send out plasma clouds that shield the Earth and cause the cosmic ray flux to decrease within half a day. The largest events cause the cosmic ray ionization to decrease by about 10-15 %.

So obviously one should look for an impact on the Earth’s aerosols and cloud cover. Our results published in GRL 2009 (reference below) show clear effects in the aerosols and in various cloud parameters. In essence the whole chain from solar activity to cosmic rays ionization to aerosol production to cloud properties can be seen. The effect is quite large — nearly 6% loss in cloud liquid water averaged over the 5 strongest events.

There have been a few papers on this subject which disagrees with our results, but they are in fact in agreement when looking more closely in accordance with our results.

There is plenty of sulphur from the phytoplankton. Over the oceans, cloud formation is limited by the cosmic ray influx, not by the sulphur supply. As for ammonia, the huge effect discovered by CLOUD is very interesting. But as they need only one ammonia molecule in 30 billion in the air, and as emissions from the oceans include an estimated at 8 Gigatonnes of ammonia, I see no constraint there. (Ammonia emissions from the land are much higher.)

(PS. The clusters made by CLOUD will in nearly all cases grow to CCN (Cloud Condensation Nucleation) size, see for example Proceedings of IPAC’10, Kyota, Japan (pages 4474-4478) where particles in the CLOUD chamber are grown to 70 nm which are CCN size. Our experiment could grow particles to 40 nm which is very close to CCN ~50 nm)

What is the changing flux of CR’s at the Earth correlated with?

The correlations that have been found so far are on long time scales star formation rates (million of years). On shorter time scales solar modulation of cosmic rays. Numerous proxies of climate seems to be correlated with changes in cosmic rays (14C or 10Be for example) – stalagmites, ice-rafted debris, tree-rings, corals etc.

What does the present low level of solar activity mean?

When the Sun became quiet, after its intensification of activity during the 20th Century, global warming stopped/paused about 10-15 years ago, and sub-surface ocean temperatures seem to be declining. In some sense the Sun will show by itself how important lack of high solar activity is in the near future.

What is the next step forward?

The above all in all implies that ions are of fundamental importance in the formation of new aerosols and for cloud properties in the Earth’s atmosphere. Of course there are many things to explore, but I think the cosmic-ray/cloud seeding hypothesis is converging with reality.

For example more experiments involving larger parameter range. Study satellite observations of cloud properties. Search for additional impact of a cosmic rays/climate link.


“Natural experiment” reference:

H. Svensmark, T. Bondo and J. Svensmark, ‘Cosmic Ray Decreases Affect Atmospheric Aerosols and Clouds’, Geophysical Research Letters, Vol: 36, pp. L15101 ff., 2009

Our lab experiment references:

H. Svensmark, J. O. Pepke Pedersen, N. Marsh, M. Enghoff and U. 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)

M. A. B. Enghoff; J. O. Pepke Pedersen; T. Bondo, M. S. Johnson, S. Paling and H. Svensmark, ‘Evidence for the Role of Ions in Aerosol Nucleation’, Journal of Physical Chemistry A, Vol: 112, pp. 10305-10309, 2008

M.B. Enghoff, J. O. Pepke Pedersen, U. I. Uggerhøj, S. M. Paling, and H. Svensmark, ‘Aerosol nucleation induced by a high energy particle beam,’ Geophysical Research Letters, 38, L09805, 2011