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Met Office Wakes Up To Solar Influence On Climate

For as long as I have been a meteorologist, the mere suggestion that solar activity could influence climate patterns has been greeted with near derision.

Quite why this has been the case is difficult to fathom. But it’s been clear for a long time that there must be a link of some kind, ever since decades ago Professor Lamb discovered an empirical relationship between low solar activity and higher pressure across higher latitudes such as Greenland.

Perhaps the art of weather forecasting has become so dominated by supercomputers, and climate research so dominated by the impact of man on global climate, that thoughts of how natural processes, such as solar variation, could influence our climate have been largely overlooked, until very recently.

In fact new research published this week & conducted by the Met Office and Imperial College London, showing how solar variability can help explain cold winters, will come as no surprise to readers of this blog.

Most studies in the past have largely focused on the sun’s brightness, but this research has discovered that it’s the variation in the sun’s Ultra Violet (UV) output that’s crucial.

According to the new paper, published in the journal Nature Geoscience, when UV output is low, colder air than normal forms over the tropics in the stratosphere. This is balanced by a more easterly flow of air over the mid-latitudes. The cold air in the stratosphere then makes its way to the surface – leading to bitterly cold easterly winds across the UK and parts of Europe.

When UV output is higher, the opposite is true, with warmer air making its way to the surface, and carried across the UK and Europe from the west.

Of course there are other factors involved in determining our weather, and this alone does not mean scientists have discovered the holy grail of long range forecasting.

Looking globally the research makes clear that the impact of the sun’s changing UV output acts to redistribute heat, with cold European winters going hand in hand with milder winters in Canada and the Mediterranean, for example, with little impact on overall global temperatures.

The work is based on an 11 year solar cycle, with the regional temperature changes associated with the peaks and troughs of the UV cycle effectively cancelling each other out over that time.

But there are some scientists who believe that there are longer term cycles, such as the bi-centennial cycle and that on average over the coming decades solar activity will decline.

If so, not only will cold European winters become more common, but global temperatures could fall, too, although the general consensus amongst most scientists at the moment is that any solar-forced decline would be dwarfed by man-made global warming.

This is an exciting time for solar physics, and its role in climate. As one leading climate scientist told me last month, it’s a subject that is now no longer taboo. And about time, too.

BBC Weather, 12 October 2011