Wobbly Universe

Long term sunspot activity shows a rise in the last century - the sun is now very active

The Sun is more active now than it has been for a millennium. The realisation, which comes from a reconstruction of sunspots stretching back 1150 years, comes just as the Sun has thrown a tantrum. Over the last week, giant plumes of have material burst out from our star's surface and streamed into space, causing geomagnetic storms on Earth.

The dark patches on the surface of the Sun that we call sunspots are a symptom of fierce magnetic activity inside. Ilya Usoskin, a geophysicist who worked with colleagues from the University of Oulu in Finland and the Max Planck Institute for Aeronomy in Katlenburg-Lindau, Germany, has found that there have been more sunspots since the 1940s than for the past 1150 years.

Sunspot observations stretch back to the early 17th century, when the telescope was invented. To extend the data farther back in time, Usoskin's team used a physical model to calculate past sunspot numbers from levels of a radioactive isotope preserved in ice cores taken from Greenland and Antarctica.
Global warming

Ice cores provide a record of the concentration of beryllium-10 in the atmosphere. This is produced when high-energy particles from space bombard the atmosphere, but when the Sun is active its magnetic field protects the Earth from these particles and levels of beryllium-10 are lower.

There was already tantalising evidence that beryllium-10 is scarcer now than for a very long time, says Mike Lockwood, from the UK's Rutherford Appleton Laboratory near Oxford.

But he told New Scientist that when he saw the data converted to sunspot numbers he thought, "why the hell didn't I do this?" It makes the conclusion very stark, he says. "We are living with a very unusual sun at the moment."

The findings may stoke the controversy over the contribution of the Sun to global warming. Usoskin and his team are reluctant to be dragged into the debate, but their work will probably be seized upon by those who claim that temperature rises over the past century are the result of changes in the Sun's output (New Scientist, print edition, 12 April 2003). The link between the Sun's magnetic activity and the Earth's climate is, however, unclear.

Journal reference: Physical Review Letters (in press in Nov 2003)

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