Sunspots indicate colder winters

But will cold conditions in Europe have any impact on the problem of global warming?

LAST WINTER WAS particularly severe – I had to drive from Cork to pick up a visitor at Dublin airport two days before Christmas in the worst conditions I can ever remember. And, the bad news now is that it looks like we are heading into a long run of severe European winters as our sun enters a phase of low magnetic output. But, you may retort, that cloud has a silver lining – surely this means the end of global warming? Alas no. This regional cooling in Europe will apparently have little effect on global warming. Much of the research on which these predictions are based was published by Michael Lockwood and collaborators in two recent papers ( Environmental Research Letters2010, 5, 024001 and 2011, 6, 034004 – see iopscience.iop.org).

Sunspots are temporary spots that are seen on the Sun as relatively darker spots. They are caused by strong magnetic activity that causes areas of reduced surface temperatures. The surrounding margins of sunspots are brighter and hotter than average and, so, an increase in sunspot numbers increases the Sun’s brightness. Sunspot numbers rise and fall in 11-year cycles, but many experts believe that this familiar cycle is now shutting down and we may be heading towards a pattern of solar inactivity unseen since the 17th century.

A historical period, known as the Maunder Minimum, named after astronomer Edward Maunder (1851-1928), lasted from 1645 to 1715, during which time very few sunspots were observed. The Maunder Minimum coincided with the coldest part of “The Little Ice Age” during which Europe and North America experienced very cold winters. Solar activity gradually increased for about 300 years following the Maunder Minimum.

Lockwood and colleagues studied solar activity using data that stretches back over the past 9,000 years, showing that solar activity increases over periods of about 300 years and then drops quickly over periods of about 100 years. We are now in a solar decline that started about 1985 and we are about half way back to a Maunder Minimum condition. The probability of the Sun returning to this minimum over the next 50 years is about 10 per cent.

Winters are cooling down. The average UK temperature over the past 20 years was 5.04 degrees. However, the last three have averaged 3.50 degrees, 2.53 degrees and 3.13 degrees respectively. The winter of 2009/2010 was the 14th coldest in 160 years. Lockwood proposes that reduced solar output particularly affects Europe because of a phenomenon called “blocking”. Blocking affects the dynamics of the jet stream, strong winds that blow westwards across the Atlantic, 7 to 12km above the Earth’s surface, and that affect our weather systems. There is one jet stream in each hemisphere and Europe lies directly below the northern hemisphere jet stream.

Changes in the magnetic activity of the Sun affect the emission of its ultraviolet light, which then affects temperature and wind patterns in the stratosphere (20 to 50km high), and these effects feed down to the lower atmosphere and affect the jet streams. This can predispose the jet stream to get caught up on itself (blocking) in an S shape over the ocean, preventing our familiar mild wet westerly winds coming in and allowing cold dry winds from the east to come over Europe.

Lockwood stresses that his results have no implications for global warming. The changes that Lockwood predicts are regional and only apply to winter, whereas climate change refers to average temperatures all year round and in all parts of the world. Colder winters in Europe have little effect on global mean temperature. When winters are colder in Europe it tends to be warmer in Greenland.

A vigorous and acrimonious public debate continues on the causes of the global warming we experienced in the 20th century. On one side a large majority of climate experts assure us that the warming is largely due to human emissions of greenhouse gases. The opposing minority side, which includes many amateur voices, insists that any warming is largely caused by natural environmental changes and not by human activities. Over the past decade the minority side has often accused the majority of ignoring the role solar activity plays in global warming. However, these recent papers by Lockwood and collaborators, all scientists from the majority side, clearly acknowledge the influence of current solar activity on regional climate but claim that this does not ameliorate man-made global warming, which remains as big a problem as before.

William Reville is a professor in the Biochemistry Dept and public awareness of science officer at UCC