Today in Forbes, I have an article bringing the layman up to speed on Henrik Svensmark and this theory of cosmic ray cloud seeding. Since his theory helped explain some 20th century warming via natural effects rather than anthropogenic ones, he and fellow researchers have face an uphill climb even getting funding to test his hypothesis. But today, CERN in Geneva has released study results confirming most of Svensmark's hypothesis, though crucially, it is impossible to infer from this work how much of 20th century temperature changes can be traced to the effect (this is the same problem global warming alarmists face -- CO2 greenhouse warming can be demonstrated in a lab, but its hard to figure out its actual effect in a complex climate system).
Much of the debate revolves around the role of the sun, and though holding opposing positions, both skeptics and alarmists have had good points in the debate. Skeptics have argued that it is absurd to downplay the role of the sun, as it is the energy source driving the entire climate system. Michael Mann notwithstanding, there is good evidence that unusually cold periods have been recorded in times of reduced solar activity, and that the warming of the second half of the 20th century has coincided with a series of unusually strong solar cycles.
Global warming advocates have responded, in turn, that while the sun has indeed been more active in the last half of the century, the actual percentage change in solar irradiance is tiny, and hardly seems large enough to explain measured increases in temperatures and ocean heat content.
And thus the debate stood, until a Danish scientist named Henrik Svensmark suggested something outrageous -- that cosmic rays might seed cloud formation. The implications, if true, had potentially enormous implications for the debate about natural causes of warming.
When the sun is very active, it can be thought of as pushing away cosmic rays from the Earth, reducing their incidence. When the sun is less active, we see more cosmic rays. This is fairly well understood. But if Svensmark was correct, it would mean that periods of high solar output should coincide with reduced cloud formation (due to reduced cosmic race incidence), which in turn would have a warming effect on the Earth, since less sunlight would be reflected back into space before hitting the Earth.
Here was a theory, then, that would increase the theoretical impact on climate of an active sun, and better explain why solar irradiance changes might be underestimating the effect of solar output changes on climate and temperatures.
I go on to discuss the recent CERN CLOUD study and what it has apparently found.