A vipers nest on the arXiv today from two groups covering the question of whether cosmic rays can trigger cloud formation and may therefore be a significant player in the global warming debate.
The thinking goes like this: cosmic rays ionise the atmosphere, triggering the formation of aerosols which in turn nucleate cloud cover. The number of cosmic rays hitting Earth is determined by the Sun’s magnetic field which follows an 11 year cycle. Cloud cover should therefore follow a similar 11-year cycle (and any other changes in the solar magnetic field over longer time scales).
The evidence is more complicated.
On the one hand, we have Vitaliy Rusov from the National Polytechnic University in Odessa, Ukraine, and colleagues who argue that the Earth’s climate is governed by only two factors: the amount of incoming solar radiation and the cosmic ray flux which determines cloud cover and therefore effects the amount of radiation that is reflected and absorbed. In two papers examining the theory and data, Rusov and co argue that carbon dioxide levels play no part in determining our climate.
On the other hand, we have Terry Sloan from the University of Lancaster and a pal who have studied the evidence that links cloud cover to cosmic ray flux. They point out that in some places the cloud cover data appears to correlate with cosmic rays, in others it anticorrelates. And since cosmic ray flux changes with latitute, so should cloud cover although there is no data to support this. They conclude that if cosmic rays do influence cloud cover, then they can be responsible for no more than 23 per cent of globally averaged cloud cover changes during the 11-year solar cycle.
I think I can see where the wind is blowing on this one. But it needs some heavyduty contemplatin’ by some serious climatologists and atmospheric physicists.
The International Panel on Climate Change has yet to pronounce on this effect and its influence on climate. But it needs to move quickly to determine whether it should be a significant part of the climate debate or a red herring.
In the meantime, expect a humdinger of a ruckus.
arxiv.org/abs/0803.2765 : Galactic Cosmic Rays – Clouds Effect and Bifurcation Model
of the Earth Global Climate. Part 1: Theory
arxiv.org/abs/0803.2766: Galactic Cosmic Rays – Clouds Effect and Bifurcation Model
of the Earth Global Climate. Part 2: Comparison of Theory with Experiment
arxiv.org/abs/0803.2298: Testing the Proposed Causal Link between Cosmic Rays and