A paper published today in Quaternary Science Reviews reconstructs climate of the central Alps over the past 10,000 years and finds precipitation and floods were driven by changes in solar activity. The authors propose variations in solar activity and insolation cause widening and shrinking of the Hadley cell, and influence on the North Atlantic Oscillation [NAO] and Intertropical Convergence Zone [ITCZ]. The paper adds to many other peer-reviewed publications finding solar amplification mechanisms by which small changes in solar activity have large effects on climate.
The authors also find floods and heavy precipitation were more common during cold periods such as the Little Ice Age than during warm periods such as the Medieval Warm Period, the opposite of claims that warming increases precipitation and floods from increased atmospheric water vapor.
According to the authors, “We found that flood frequency was higher during cool periods, coinciding with lows in solar activity. In addition, flood occurrence shows periodicities that are also observed in reconstructions of solar activity from 14C and 10Be records (2500–3000, 900–1200, as well as of about 710, 500, 350, 208 (Suess cycle), 150, 104 and 87 (Gleissberg cycle) years). As atmospheric mechanism, we propose an expansion/shrinking of the Hadley cell with increasing/decreasing air temperature, causing dry/wet conditions in Central Europe during phases of high/low solar activity. Furthermore, differences between the flood patterns from the Northern Alps and the Southern Alps indicate changes in North Atlantic circulation.”
More here, including the graphs: http://hockeyschtick.blogspot.com/2013/10/new-paper-finds-another-amplification.html
As solar activity declines we can expect more cooling, more floods and I predict more sever storms. Reading the history of the Maunders Minimum, from the scant records, life was very difficult with many sever storm events. We are now headed in that direction.
I still don’t know why these scientist do not read Marcel Leroux’s work on Mobile Polar Highs whose dynamic explains perfectly flood occurrences during different climatic periods, instead of talking about the Hadley cell which does not exist.