From Sun and Liu 2012: all of the deep solar minima of the last millennium (Oort, Wolf, Spörer, Maunder and Dalton) correspond to periods of drought in the Qilian Mountains of the northeastern Tibetan Plateau according to this tree-ring study.
Guest post by Alec Rawls
Like the Central Asian precipitation study that Anthony posted about yesterday, this one also comes via a review by “Cold Sun” authors Sebastian Lüning and Fritz Vahrenholt, as translated by Pierre Gosselin.
Using tree ring width as a proxy for precipitation (about a 50% correlation over the period of the instrumental rainfall record) Chinese scientists Junyan Sun and Yu Liu found the remarkable correspondence between solar activity and precipitation seen in the graph above. As summarized by Lüning and Vahrenholt:
The Great Drought occurred during a weak period of solar activity, the so-called Spörer Minimum, which occurred from 1420 to 1570. Interestingly, almost all other periods of drought occurred during times of solar minima, among them the Oort Minimum, Wolf Minimum, Maunder Minimum and Dalton Minimum. Every time the sun goes into a slumber for a few decades, the rains on the Tibetan Plateau stay away.
A frequency analysis of precipitation curves also delivers evidence on solar cycles. Here the Gleissberg Cycle (60-120 year period) and the Suess/de Vries Cycle (180-220 years) are seen in the datasets.
Yesterday’s study, which also looked at the Tibetan Plateau but about 1400 kilometers to the west, found the opposite relation, with “Bond events” (episodes of ice rafting in the North Atlantic, which Bond identified with periods of low solar activity), corresponding to periods of higher humidity (colder and wetter) in the Taklamakan Desert. The two studies taken together seem to suggest a solar driven shift in weather patterns.
Is this support for Stephen Wilde’s theory about high solar activity pushing the polar jet stream northward? Any significant change in the jet stream would likely cause its latitudinal waves to shift as well, so even though the two Tibetan sites are at the same latitude, it is plausible that rainfall in the two locations could be oppositely affected by the sun.
In general, if solar activity is by any mechanism a powerful driver of climate then corresponding changes in weather patterns would seem to be unavoidable. This would account both for the high number of studies that find solar signals in paleo-climate proxies and for the difficulty in fitting these studies together into a larger picture. Maybe with enough more precipitation studies at enough locations a coherent map of fluctuating weather patterns will emerge.
Are there enough old Coastal Redwoods to do tree ring studies up and down a thousand miles of Pacific coast? If Redwood rings correlate well with precipitation, that could be a good place to look for shifting weather patterns. Has this already been done? The Save the Redwoods group claims to be compiling their own such database now. Maybe it will show something.
On the difficulty of finding simple relationships, note that the correlation Sun and Liu found between solar activity and precipitation in the Qilian Mountains goes wobbly over the last dozen decades. If the correspondence between low solar activity and dry weather at this location is real then it seems that the 1900 lull in solar activity was not deep enough to trigger the changed weather pattern. Precipitation was actually high across the 1900-lull, then was below average in the 1940s, 50s and 60s when the sun was particularly active.
It’s a reminder to take the remarkable coincidence between precipitation and deep solar minima in the Qilian Mountains with a grain of salt. In any one location the relationship between climate and weather is going to be noisy, which not only can obscure real relationships but can also point to false ones. Still, the evidence for a powerful solar driver of climate keeps piling up.