A new experiment with old apparatus reveals a flaw in models of the climate.
CLOUD chambers have an honoured place in the history of physics. These devices, which generate vapour trails that mark the passage of high-energy subatomic particles, were the first apparatus that allowed such passage to be tracked. That was in the 1920s and led, among other things, to the discovery of cosmic rays. Science has moved on since then, of course, and cloud chambers are now largely museum pieces. But the world’s leading high-energy physics laboratory, CERN, outside Geneva, is dusting the idea off and putting it into reverse. Instead of using clouds to study cosmic rays, it is using cosmic rays to study clouds. In doing so, it may have thrown a spanner into the works of the world’s computer models of the climate.
Clouds are formed by the condensation of water vapour in the atmosphere around clusters of molecules such as ammonia and sulphuric acid. Ions created by the passage of cosmic rays can trigger the formation of such molecular seeds—a process of particular interest because the arrival of cosmic rays is regulated, in part, by the sun. The 11-year solar cycle, which governs the appearance of sunspots, also changes the sun’s magnetic field. That, in turn, affects the passage of cosmic rays (which are mostly protons released by distant supernova explosions), and thus the number of such rays that make it to Earth. Since clouds help regulate the climate, by reflecting sunlight back into space and cooling the atmosphere, some researchers think cosmic rays are a means by which changes in solar activity are translated into terrestrial climate change.
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