Previous TRF articles about the experiment:
The summary? They confirm that the clouds are being nucleated by the radiation at the rate that was expected in the newest models, whatever these models are (and be sure I would like to see some details, too). So the effect is surely nonzero.
Henrik Svensmark told me a year ago that the CLOUD experiment is somewhat redundant because the existence of the basic effect behind cosmoclimatology has already been pretty much established by their own experiments in Denmark. But it may be true that the CERN logo is needed for some additional people to notice.
So it's coming and the result is Yes, it works.
Note that as many children know, clouds have a big effect on the temperature of the Earth. They subtract something like 30 W/m^2 from the energy budget in average; this is about eight times more than the contribution attributed to the CO2 doubling in the man-made theory of climate change. If you wish, you would need to increase the CO2 concentration approximately by 256 to match the contribution of the clouds. ;-)
So even small variations of the cloudiness matter.
However, as Richard Lindzen has emphasized to me in June 2010 in Nice, one must avoid naive assumptions about the mechanisms that control the actual cloudiness expressed as the percentage of the sky. Cosmic rays may make it easier for clouds to appear.
But the result may be simply that the clouds get created 50 meters lower or 50 meters higher than they would be created without the cosmic rays; the overall percentage of the cloudy skies may be determined by something like "wind going up" and "wind going down", if you allow me to use a layperson's language and the percentage of both is 50%. The actual cloudiness is not 50% but you may imagine that a more complicated mechanism of this sort is at work and it makes the cloudiness pretty much constant.
However, Richard doesn't have a complete proof that the "cloudy subsidies" from the cosmic rays really have to cancel when it comes to their overall effect on the cloud cover. Some spectacular correlations similar to one above suggest that the cosmic rays could be correlated with the cloudiness for a good reason. And the cloudiness is known to be variable; it dropped by 3% in the 1980s, for example.
Moreover, you may argue that Richard overestimates the desire of Mother Nature to regulate herself and suppress all external effects - whether they're caused by carbon dioxide or cosmic rays - by powerful negative feedbacks. While I think that negative feedbacks ultimately prevail, I obviously don't feel that they're as powerful as Richard Lindzen's negative feedbacks. ;-)
These comments are just meant to convey the obvious message that a lab experiment doesn't settle all questions about the global climate, especially not in the long term. However, it's clear that the potential of the cosmic rays as a climate driver will be established by showing this local effect that will be as real as the infrared absorption by the greenhouse gases. Much more is needed to decide which of these effects actually matter for the weather and the climate in the real world, outside the lab.
Via Anthony Watts