Sebastian Lüning recently wrote a piece on a new study by a French team of scientists. Conclusion: Mediterranean storm activity decreases during warm periods and there appears to be a solar link.
The worst storms at the French Mediterranean coast? Always when the sun was weak and temperatures declined!
By Daniel Albig and Sebastian Lüning
(Translated by P Gosselin with permission)
The area of the Mediterranean Sea is regarded as a region that reacts especially sensitively to climate fluctuations. An increase in temperature there would be especially noticeable, say certain model projections. In 2007 some scientists even prophesied that there would soon be a danger of cyclones forming at the Mediterranean. But what does the pre-industrial climate history tell us about this possibility? Is there really a relationship between storm activity and temperature in the Mediterranean region?
A French team of scientists led by geologist Pierre Sabatier studied in detail how storms and global warming behaved historically in the region. In a study that appeared in January 2012 in the journal Quaternary Research, they examined the last 7000 years. The basis for their study was an 8-meter long sediment core that had been extracted in March, 2006 from the seabed of the Pierre Blanche Lagoon of the southern French Golf of Lion, about 10 kilometers south of Montpelier.
The scientists studied changes in the deposits in the lagoon, which today are covered by 60 cm of water. Changes in storm patterns in the region can be discerned by the variations in the particle size of the sand, the clay composition and fossils present. The frequency of the various species of water snails were analyzed. For example the hydrobia acuta lives in the brackish waters, the bittium reticulatum lives in the open seas. A sudden increase in deposits of the needle whelk indicates greater storm activity because the lagoon gets flooded more often by the sea.
Using various indicators, the French scientists identified seven periods of increased solar activity: 6300-6100 years ago, 5650-5400 years ago, 4400-4050 years ago, 3650-3200 years ago, 2800-2600 years ago, 1950-1400 years ago and 400-50 years ago. Storm activity increased over and over again over the last few thousands of years, and settled down during the times in between.
So what could have triggered storm activity at the French Mediterranean? In the search for possible relationships, the French scientists compared storm development with the temperature development of the North Atlantic, which was reconstructed more than 10 years ago by a team led by Gerard Bond who examined cores of ice berg rafted sediment and published the results in the journal Science. The Bond group could show that the temperature cycles were in sync with solar activity.
And what did this comparison yield? Storms in the Northwest Mediterranean occurred more often during the cold periods. Solar activity played an important role: Whenever the sun weakened, it became cold and stormy. When the sun got active, temperatures increased and the winds died down (Figure 1). The main drivers were obviously the solar Bond cycles. Also added are some solar-dependent, climate-system-internal fluctuations which complete the picture.
How could the relationship function? The scientists suspect that a stark north-south temperature gradient prevailed during the cold periods and thus resulted in more storms. In addition the westerly winds could have shifted southwards.
If you look back at the last 1000 years, the natural pattern becomes clear. During the Medieval Warm Period (1150 to 650 years ago) the new research results show that a period of weak storm activity prevailed. During the Little Ice Age that followed, tempestuous storms raged over the area of study. During the transition to the current Modern Warm Period the storms died down. The good news: An increase in storm activity is not anticipated, at least for the south French coast, with further warming of the Earth. Instead a decrease in storm activity is expected.
Interestingly, the relationship is not only valid for the Mediterranean region. Already in February 2012 we reported on a study from the Netherlands. That study showed that the strongest storms occurred during the Little Ice Age (read: Die kräftigsten Stürme gab es in Holland während der Kleinen Eiszeit).