Quiet sun puts Europe on ice
14 April 2010 by Stuart Clark
BRACE yourself for more winters like the last one, northern Europe. Freezing conditions could become more likely: winter temperatures may even plummet to depths last seen at the end of the 17th century, a time known as the Little Ice Age. That's the message from a new study that identifies a compelling link between solar activity and winter temperatures in northern Europe.
The research finds that low solar activity promotes the formation of giant kinks in the jet stream. These kinks can block warm westerly winds from reaching Europe, while allowing in winds from Arctic Siberia. When this happens in winter, northern Europe freezes, even though other, comparable regions of the globe may be experiencing unusually mild conditions.
Northern Europe freezes, even though comparable regions experience unusually mild conditions
Mike Lockwood at the University of Reading in the UK began his investigation because these past two relatively cold British winters coincided with a lapse in the sun's activity more profound than anything seen for a century. For most of 2008-9, sunspots virtually disappeared from the sun's surface and the buffeting of Earth by the solar magnetic field dropped to record lows since measurements began, about 150 years ago.
Lockwood and his colleagues took average winter temperatures from the Central England Temperature dataset, which extends back to 1659, and compared it with records of highs and lows in solar activity. They found that during years of low solar activity, winters in the UK were far more likely to be colder than average. "There is less than a 1 per cent probability that the result was obtained by chance," says Lockwood, in a paper to appear in Environmental Research Letters.
Judith Lean, a solar-terrestrial physicist at the US Naval Research Laboratory in Washington DC, says the analysis is statistically robust, and reckons it forms a piece in the larger puzzle of how solar activity influences weather. Often cited by climate-change sceptics as a cause of global warming (see "What are you up to, sunshine?"), the effects of solar cycles have largely evaded the grasp of climate modellers. Lockwood found that when he removed 20th-century warming due to industrial emissions from his models, the statistical link between solar lows and extreme winters was stronger, suggesting the phenomenon is unrelated to global warming. But the sun undeniably has a big influence on weather systems: it is, after all, the energy source that powers them.