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Does Earth鈥檚 magnetic field affect the weather?

Mike Follows Sutton Coldfield, West Midlands, UK

The jury is still out, but the verdict is likely to be that there is no causal link between Earth鈥檚 magnetic field and our weather.

A possible link was suggested by Danish physicist Henrik Svensmark in his galactic cosmic ray hypothesis. This proposes that protons in cosmic rays blasted out by exploding stars called supernovae collide with our atmosphere. According to the hypothesis, this creates condensation nuclei, leading to cloudier skies, colder weather and a cooler climate.

When the magnetic fields of the sun or Earth are strong, there is greater deflection of the charged particles of galactic cosmic rays, so there should be fewer clouds and the weather and climate should be warmer. Conversely, when the magnetic fields are weaker, the prevailing weather should be cloudier and colder.

Evidence that appears to support this hypothesis comes from the so-called Maunder Minimum, which occurred between 1645 and 1715. During this period, the sun had fewer sunspots 鈥� cooler, darker areas on its surface. This happens when the sun鈥檚 magnetic field is weaker, so at that time there was less deflection of cosmic rays in the solar system and hence, if Svensmark is correct, cloudier and colder weather on Earth.

At the same time as the Maunder Minimum, Europe was enduring the Little Ice Age, in which temperatures fell low enough for 鈥渇rost fairs鈥� to be held on the river Thames.

This possible link between galactic cosmic rays and cloud formation is being tested at the CERN particle physics lab near Geneva, Switzerland. There, the Proton Synchrotron is being used to produce high-energy protons to mimic galactic cosmic rays. These are being fired at the CLOUD experiment, which is basically a chamber of very clean air. The fact that there are other sources of condensation nuclei complicates the picture, and so far, the results of the tests aren鈥檛 clear-cut.

Svensmark鈥檚 hypothesis is elegant, but, to paraphrase Thomas Huxley, 鈥渕any a beautiful theory was killed by an ugly fact鈥�.

To answer this question 鈥� or ask a new one 鈥� email lastword@newscientist.com.

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