Monday, October 16, 2006

Cosmic Rays and Climate Change: RealClimate's analysis

The always interesting RealClimate blog has an interesting analysis of a paper by Svensmark et al [Svensmark, H., et al, 2006, Proc. Royal. Soc. A., xx, 1364] investigating whether Cosmic Rays can promote low altitude cloud formation, a paper with the snappy title "Experimental evidence for the role of ions in particle nucleation under atmospheric conditions"

The paper itself (go read it) is pretty innocuous and hardly applies their results to anything, but the press release isn't shy about explaining the (supposed) implications:

"A team at the Danish National Space Center has discovered how cosmic rays from exploding stars can help to make clouds in the atmosphere. The results support the theory that cosmic rays influence Earth’s climate."

Here are some more choice bits from the press release:

The experimental results lend strong empirical support to the theory proposed a decade ago by Henrik Svensmark and Eigil Friis-Christensen that cosmic rays influence Earth’s climate through their effect on cloud formation. The original theory rested on data showing a strong correlation between variation in the intensity of cosmic radiation penetrating the atmosphere and the amount of low-altitude clouds. Cloud cover increases when the intensity of cosmic rays grows and decreases when the intensity declines.

It is known that low-altitude clouds have an overall cooling effect on the Earth’s surface. Hence, variations in cloud cover caused by cosmic rays can change the surface temperature. The existence of such a cosmic connection to Earth’s climate might thus help to explain past and present variations in Earth’s climate.

Interestingly, during the 20th Century, the Sun’s magnetic field which shields Earth from cosmic rays more than doubled, thereby reducing the average influx of cosmic rays. The resulting reduction in cloudiness, especially of low-altitude clouds, may be a significant factor in the global warming Earth has undergone during the last century. However, until now, there has been no experimental evidence of how the causal mechanism linking cosmic rays and cloud formation may work.

Its not quite claiming that ALL climate change is due to changes in the Cosmic Ray irradiance, but its not making any attempt to say this might only be a small effect.

If you're interested in a discussion of the physics, and why Gavin at RealClimate isn't buying the PR spin, then go over to RC.

What I'd like to know is who chose to put the emphasis in the press release on climate change? It certainly sounds like it was written by someone who doesn't believe that human activity is responsible for the unprecedented climate change in the 20th century.

Buts its not clear to me as yet that we know who put this spin into the press release.

Within the last year we've seen the case of a unqualified political hack who somehow got a job in the NASA press office editing scientific press releases to reflect his personal beliefs, and attempting to cut of press access to a prominent climate scientist. Perhaps something similar has happened in this case?

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