Opinion A team of boffins in Germany say they have found a statistical link between periods of low solar activity and very cold winters in Europe. Some physicists believe that a long period of low solar activity - like the "Maunder Minimum" of the 17th and 18th centuries - could be on the cards in coming decades, so the new research might indicate an upcoming "mini Ice Age".
The new study was published over the weekend in the journal Geophysical Research Letters. Lead author Professor-Doktor Frank Sirocko of the Johannes Gutenberg Universität (University) of Mainz in Germany - and his colleagues - compared old records showing which years the Rhine river iced over to the record of sunspot activity.
According to the JGU statement:
Sirocko and his colleagues found that between 1780 and 1963, the Rhine froze in multiple places fourteen different times.
Mapping the freezing episodes against the solar activity's 11-year cycle, a cycle of the Sun's varying magnetic strength and thus total radiation output, Sirocko and his colleagues determined that 10 of the 14 freezes occurred during years when the Sun had minimal sunspots. Using statistical methods, the scientists calculated that there is a 99% chance that extremely cold Central European winters and low solar activity are inherently linked.
"The sheer size of the Rhine river means it takes extremely cold temperatures to freeze over making freezing episodes a good proxy for very cold winters in the region," comments Sirocko. "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."
Normally the Sun varies its activity on a regular 11-year cycle, indicated by the prevalence of sunspots on its surface. However there was a well-documented period from around 1645 to 1715 AD - the "Maunder Minimum" - when there were no sunspots. As NASA notes:
Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented. This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes. There is evidence that the Sun has had similar periods of inactivity in the more distant past. The connection between solar activity and terrestrial climate is an area of on-going research.
Solar-driven climate shifts are topical right now, because major solar physicists are forecasting that another Maunder Minimum may be imminent, based on trends seen in solar activity over the past few cycles. If they and Sirocko are right, bitterly cold winters like those of 2010 and 2011 (which saw various records for low temperature broken across Europe) could become much more common.
"Climate is not ruled by one variable," argues the Professor-Doktor. "In fact, it has at least five or six variables. Carbon dioxide is certainly one, but solar activity is also one."
Nonetheless the idea that the Sun has climate effects comparable to carbon emissions is vastly controversial and mentioning such things will always draw a storm of abuse. Before daring to announce Sirocko's study, press officers sought comment from an independent expert boffin: Thomas Crowley, Director of the Scottish Alliance for Geoscience, Environment, and Society, who was not involved with the study.
"Sirocko and his colleagues have added to the research linking solar variability with climate," Crowley told the Germans. "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."
The study itself can be read by subscribers here. ®