Accelerator results on cloud nucleation (2)


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Did you get the message?

I’m not sure that the significance of my 15 May post, about the accelerator experiment in Aarhus, has been fully grasped. Following my 13 May post, the blogosphere seems to be still in a “waiting for CLOUD” mode. Yes, it will indeed be fascinating to see the first results from CERN’s CLOUD experiment in two or three months’ time, but meanwhile we have the results from Denmark. Perhaps I was negligent in not giving a little history.

The first laboratory test of the Svensmark hypothesis was the SKY experiment in Copenhagen, the outcome of which was published by the Royal Society of London in 2007. The positive results were of course politically incorrect, because Henrik Svensmark’s discovery of the effect of cosmic rays on clouds gave the Sun a much larger role in climate change than supporters of the man-made global warming hypothesis would like to admit.

The warmists were offered a delaying tactic by physicists who said, “Ah, but the SKY people used only natural cosmic rays and radioactive sources. Don’t believe them unless the CLOUD experiment in Geneva, simulating the cosmic rays with a fully controllable beam of accelerated particles, gets similar results.”

Conveniently for the warmists, CLOUD was very slow to get going. Meanwhile the Danes continued with their own experiments, including the one using an accelerator at Aarhus, as reported in Geophysical Research Letters a few days ago. The most important points are:

  • The effect of cosmic rays in helping to seed cloud formation is verified with a particle accelerator, just as critics of SKY were demanding four years ago.
  • A simple radioactive gamma-ray source gave just the same results in the Aarhus set-up so the earlier insistence, that only an accelerator experiment would do, was unwarranted.

Nevertheless, let’s say good luck to the CLOUD team. Their big chamber should be able to trace the growth of aerosol seeds much farther than in the small chamber used at Aarhus. And they have a large programme of future work, simulating atmospheric conditions at different altitudes.

See the Aarhus University press release that came out yesterday evening:

For references and other links, see my previous post:

For a video interview with Jasper Kirkby of CLOUD see:

Added 18 May: Ah, now the word is spreading. See

Anthony Watts:

David Whitehouse:

The second item quotes me directly, and at the end of the second paragraph I should really have said ionizing “gamma rays” instead of “particles” — I amended it on this blog a few hours after posting it.

Added 20 May: Friendly words from The Scientific Alliance