Cold European Winters Could Be Sun Connected.
For those who enjoy solar studies, we’re sure you’ve often wondered if the 11-year sunspot cycle could be responsible for terrestrial weather changes.
Unfortunately, reliable and accurate weather records don’t exist far back enough to confirm that specific weather patterns could be correlated to solar activity. Now, thanks to a rather unique observation, an international team of researchers may be able to show that unusually cold winters in Central Europe may occur when sunspots are at a minimum.
Just what minor clue tipped the researchers into drawing comparisons? Try the freezing of Germany’s largest river – the Rhine. “The advantage with studying the Rhine is because it’s a very simple measurement,” said Frank Sirocko lead author of a paper on the study and professor of Sedimentology and Paleoclimatology at the Institute of Geosciences of Johannes Gutenberg University in Mainz, Germany. “Freezing is special in that it’s like an on-off mode. Either there is ice or there is no ice.”
Oddly enough, records of the freezing of the Rhine date back almost two centuries. Thanks to careful logging of weather conditions by riverboat men who used the waterway for transport, we have a record of when ice congested the area and shut down shipping. Scientists used these documents, along with other historical records, to determine the freezing incidents since 1789. Sirocko and his team discovered several incidences of freezing between 1789 and 1963 – a total of 14 separate times. “The sheer size of the river means it takes extremely cold temperatures to freeze over, making freezing episodes a good proxy for very cold winters in the region,” Sirocko said.
Next up came comparing historical records against the sunspot cycle. Because this type of activity means differing levels of magnetic strength, it also means a variance in total radiation output. Sirocko and his colleagues determined that 10 of the 14 freezes occurred during years around when the Sun had minimal sunspots – leaving a 99% chance that these extreme cold conditions and sunspot activity are linked. “We provide, for the first time, statistically robust evidence that the succession of cold winters during the last 230 years in Central Europe has a common cause,” Sirocko said.
Researchers have linked low solar activity to a localized, temporary cooling of Central Europe, by studying the freezing of the Rhine river (CREDIT: Warburg, via Wikimedia Commons)
Through this new research, Sirocko and the team have embellished on their theory by adding further information, such as solar variability versus climate – an idea supported by Thomas Crowley, Director of the Scottish Alliance for Geoscience, Environment, and Society, who was not involved with the study. “There is some suspension of belief in this link,” Crowley said, “and this study tilts the argument more towards thinking there really is something to this link. If you have more statistical evidence to support this explanation, one is more likely to say it’s true.”
So, exactly what type of impact could sunspot numbers impart on Earth’s weather? Let’s consider the facts. When sunspot numbers are low, the Sun produces less ultraviolet radiation. This, in turn, means less heating of our atmosphere and causes change in the circulation pattern of the lower atmospheric levels – the troposphere and the stratosphere. These changes cause atmospheric pressure variations, such as the North Atlantic Oscillation, which impacts weather in Europe. “Due to this indirect effect, the solar cycle does not impact hemispherically averaged temperatures, but only leads to regional temperature anomalies,” said Stephan Pfahl, a co-author of the study who is now at the Institute for Atmospheric and Climate Science in Zurich.
Full-disc view of the X-ray Sun and shows a quite active corona from near the maximum of the solar cycle. At the upper right one can see an "X-ray jet" squirting outwards. (Photo credit: Wikipedia)
With their work, the researchers have shown that changes in atmospheric circulation leads to cooling in central Europe, yet sparks a warming trend in other European countries which you wouldn’t expect, such as Iceland. This means that a lower sunspot count doesn’t particularly mean global cooling.
“Their cooling effect is more localized,” Sirocko said. He also stated that studies have suggested the extreme winters of 2010 and 2011 were the result of the North Atlantic Oscillation, which Sirocko and his team now link to the low solar activity during that time.
These European winters were so cold they actually set records! ” But climate is a complex system,” Sirocko said. And a short-term, localized dip in temperatures only temporarily masks the effects of a warming world.
“Climate is not ruled by one variable,” said Sirocko. “In fact, it has [at least] five or six variables. Carbon dioxide is certainly one, but solar activity is also one. “
Despite the tidy explanation of a solar cycle driven weather pattern, there is still overwhelming evidence that our Earth is warming – and the average temperatures of those Rhine freezing winters has steadily increased over the last 30 years. In fact, the Rhine hasn’t frozen over since 1963.
To help further embellish their studies, the researchers are also looking into other historical avenues in which temperature may have played a role, such as the spread of diseases and migratory patterns.
“Disease can be transported by insects and rats, but during a strong freezing year that is not likely,” said Sirocko. “Also, Romans used the Rhine to defend against the Germanics, but as soon as the river froze people could move across it.
The freezing of the Rhine is very important on historical timescales.”
To just what does Sirocko owe his inspiration? As romantic as the Rhine may sound, it wasn’t freezing rivers and sunspot activity which got him to thinking.
It was, in fact, a 125 mile Netherlands ice-skating race which he attended two decades ago “Skaters can only do this race every 10 or 11 years because that’s when the rivers freeze up,” Sirocko said. “I thought to myself, ‘There must be a reason for this,’ and it turns out there is.”
Original Story Source: American Geophysical Union News Release.
