Sunspots and climate: a new frozen connection

by Bill Chameides | September 5th, 2012
posted by Erica Rowell (Editor)

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The freezing of the Rhine River is linked to sunspots with a global warming smoking gun.

Sure, scientists can get their inspiration from strange associations, but who’d have thought an ice skating race could spark significant insight into how the climate works? That appears to be the case for Frank Sirocko of Johannes Gutenberg University Mainz, Germany, and colleagues, who reported in a paper in the journal Geophysical Research Letters on an intriguing relationship between sunspot activity and cold winters in Europe.

The story begins with two seemingly disparate facts.

Recent European winter chill

In case you don’t remember, at times, the European winters of 2010, 2011 and 2012 were unusually cold. We even wrote about it a few times (here, here and here). And several scientific papers have pointed out that circulation patterns were unusual (see here, here and here), allowing cold Arctic air to escape the polar regions and bring snow and colder temperatures to the mid-latitudes including parts of Europe.

Some research has linked the changed circulation patterns to the dramatic loss of Arctic sea ice in recent years. If that’s the case, we may be in for more of the same this winter as this season’s melt has already exceeded the previous low set in 2007. And the six lowest extents have all occurred in the last six years. (See here and here.)

But could there be other factors contributing to extreme freezes? That question leads us to the next fact.

A 125-mile ice skating race

If you’re like me, you’ve never heard of the Elfstedentocht, but it’s a pretty big deal for many who hail from the Netherlands. Elfstedentocht is Dutch for “11 Cities Tour,” and it specifically refers to an ice skating race. The race only occurs when the temperatures are cold enough to completely freeze a network of canals, rivers and lakes that ring the Dutch province of Friesland, an occurrence that allows skaters to race a distance of 125 miles and through 11 cities.

Given that the Elfstedentocht can only be held when the entire course is sufficiently frozen to support thousands of racers, it’s a relatively rare event. The first race was held in 1909 and thereafter it was held in intervals of as long as 22 years to as short as consecutive years. The last three were held in 1985, 1986 and 1997, but thawing brought the 1985 race to an early grinding halt.

A sunspot connection?

And this is where Sirocko and colleagues come in. Last winter, while the unusually cold weather fed Elfstedentocht fever throughout the Netherlands (but, alas, to no avail), the researchers began thinking about the fact that the cold weather waas occuring at the same time as a deep minimum in sunspot activity.* Was that, the researchers wondered, simply a coincidence or could the sunspot minima be a trigger for cold winters in Europe?

To answer that question the researchers attempted to see if there was a correlation between the Rhine freezing over (as a proxy for “cold” winters) and sunspot activity over the past 230 years. The authors chose the freezing of the Rhine as their proxy because, given the long use of the river for shipping and transport, it is a well-documented event as well as a simple one to document.

The results of their analysis are pretty striking. Over the last 230 years there have been 14 “freezes,” and 10 of them have occurred in years near solar minima. Statistically the researchers found that there was only a one percent probability that the correlation was a random coincidence. The authors speculate that the connection between sunspots and cold European winters is being driven by the following mechanisms:

  • Low sunspot activity,
  • Lower influx of energetic particles and ultraviolet rays from the Sun and
  • Lower stratospheric temperatures propagated down into the troposphere, triggering a shift in the circulation patterns in the North Atlantic and regional weather in Europe, such that cold air flows from the Arctic and Scandinavia towards central Europe, leading to colder temps over parts of central Europe.

Interesting, don’t you think? And here’s another interesting tidbit. The last time the Rhine froze in accordance with Sirocko et al’s definition was in 1963. Despite the proximity to cycle 23’s prolonged solar minima (see here and here), neither the Rhine nor the canals of Friesland froze during the winter of 2010 or 2011. How come? Well, global warming comes to mind.


End note

* One measure of solar activity is the number of sunspots that appear on the Sun’s surface as it moves through its 11-year solar cycle. At the height of a cycle, the Sun grows lots of sunspots and puts out a bit more energy. At a cycle’s nadir, there are fewer sunspots and a bit less energy. And not all solar cycles are created equal — some are stronger or more active with more sunspots and more energy radiated; some are less active, with fewer sunspots and less energy. Cycle 23 (which had a prolonged minimum) just ended in December 2008. Fore more, see previous posts here and here.

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