Climate Change – News and Comments
Maps of monsoon history
“Asian Monsoon Failure and Megadrought During the Last Millennium” is the dramatic title of a report in Science that introduces a new Monsoon Asia Drought Atlas. Edward R. Cook and his colleagues at the Tree-Ring Laboratory of Columbia University’s Lamont-Doherty Earth Observatory have used tree-rings from 300 sites in Asian forests to reconstruct the summer “Palmer Drought Severity Index” (PDSI) across India, China and adjacent regions. PDSI is a fairly complicated reckoning of local deviations from mean conditions, originated in 1965 by Wayne C. Palmer, a climatologist in the US Weather Bureau.
In the following examples, North American data supplement the Asian PDSI, and anomalous sea-surface temperatures (SST) across the Pacific are also reconstructed.
The event of 1876-79 was the exceptionally severe “Victorian Great Drought,” afflicting especially British India, French Indo-China and the Dutch East Indies. Parts of western North America were also dry, although Mexico and the Pacific Northwest were abnormally wet. It coincided with a very strong El Niño in the Pacific, indicated by the red tongue of warm surface water stretching westward across the Equator.
As for 1918-19, this “Post World War I Drought” has perhaps been underrated compared with the four well-known “megadroughts” of the past millennium: the “Ming Dynasty Drought” (1638-41), the “Strange Parallels Drought” (1756-68) (17), the “East India Drought” (1790-96) and the “Victorian Great Drought” (1876-78).
Benjamin Giese, an oceanographer at Texas A&M, has recently suggested that the El Niño coinciding with the 1918-19 event was greatly underestimated because of restricted observations in the Pacific during the last year of the war. Ashore, India suffered badly again, with the global Spanish Flu pandemic increasing the death toll in the malnourished population. There was drought in South-East Asia too, but in North America the drought was further north than in 1876-79, and the north-east Pacific was cool.
By the way, the name given to the 1756-68 events – Strange Parallels – is the title of a book about South-East Asian history by Victor Lieberman at the University of Michigan. So the climate reconstructions will shed new light on global political history.
The tricky regional variations and long-distance connections of the monsoons have tantalized meteorologists and climate physicists for more than a century. With half of mankind relying on the Asian monsoon rains – often living on a knife-edge between floods and droughts – reliable predictions for even a few months ahead remain elusive.
Concerning man-made global warming, Cook and his colleagues comment only that “Monsoon failures over Asia in the modern anthropogenic period have at times been exceeded in magnitude and persistence over the past millennium.”
They make no mention of the very well-documented solar influence on the Asian monsoon, but you’ll find a general discussion of Monsoons and the Sun under Climate Change: Updating The Chilling Stars.
Edward R. Cook, et al., Science, Vol. 328, p. 486, 2010
B. S. Giese et al., Bull. Am. Meteorol. Soc, Vol. 91, p. 177, 2010
The Monsoon Asia Drought Atlas is available at http://iridl.ldeo.columbia.edu/SOURCES/.LDEO/.TRL/.MADA/
Victor Lieberman, Strange Parallels: Volume 2, Mainland Mirrors: Europe, Japan, China, South Asia, and the Islands: Southeast Asia in Global Context, c.800-1830, Cambridge UP 2009.