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The Indian Summer Monsoon
Reference
Sinha, A., Cannariato, K.G., Stott, L.D., Cheng, H., Edwards, R.L., Yadava, M.G., Ramesh, R. and Singh, I.B. 2007. A 900-year (600 to 1500 A.D.) record of the Indian summer monsoon precipitation from the core monsoon zone of India. Geophysical Research Letters 34: 10.1029/2007GL030431.

What was done
The authors derived a nearly annually-resolved record of Indian summer monsoon (ISM) rainfall variations for the core monsoon region of India that stretches from AD 600 to 1500 based on a 230Th-dated stalagmite oxygen isotope record from Dandak Cave, which is located at 1900'N, 8200'E.

What was learned
Sinha et al. report that "the short instrumental record of ISM underestimates the magnitude of monsoon rainfall variability," and they state that "nearly every major famine in India [over the period of their study] coincided with a period of reduced monsoon rainfall as reflected in the Dandak δ18O record," noting two particularly devastating famines that "occurred at the beginning of the Little Ice Age during the longest duration and most severe ISM weakening of [their] reconstruction." In addition, they state that "ISM reconstructions from Arabian Sea marine sediments (Agnihotri et al., 2002; Gupta et al., 2003; von Rad et al., 1999), stalagmite δ18O records from Oman and Yemen (Burns et al., 2002; Fleitmann et al., 2007) and a pollen record from the western Himalaya (Phadtare and Pant, 2006) also indicate a weaker monsoon during the Little Ice Age and a relatively stronger monsoon during the Medieval Warm Period."

What it means
The eight researchers note that "since the end of the Little Ice Age, ca 1850 AD, the human population in the Indian monsoon region has increased from about 200 million to over 1 billion," and that "a recurrence of weaker intervals of ISM comparable to those inferred in our record would have serious implications to human health and economic sustainability in the region," which suggests that the Current Warm Period the earth is experiencing is something for which a sizable fraction of the planet's population should be very thankful.

References
Agnihotri, R., Dutta, K., Bhushan, R. and Somayajulu, B.L.K. 2002. Evidence for solar forcing on the Indian monsoon during the last millennium. Earth and Planetary Science Letters 198: 521-527.

Burns, S.J., Fleitmann, D., Mudelsee, M., Neff, U., Matter, A. and Mangini, A. 2002. A 780-year annually resolved record of Indian Ocean monsoon precipitation from a speleothem from south Oman. Journal of Geophysical Research 107: 10.1029/2001JD001281.

Fleitmann, D., Burns, S.J., Mangini, A., Mudelsee, M., Kramers, J., Neff, U., Al-Subbary, A.A., Buettner, A., Hippler, D. and Matter, A. 2007. Holocene ITCZ and Indian monsoon dynamics recorded in stalagmites from Oman and Yemen (Socotra). Quaternary Science Reviews 26: 170-188.

Gupta, A.K., Anderson, D.M. and Overpeck, J.T. 2003. Abrupt changes in the Asian southwest monsoon during the Holocene and their links to the North Atlantic Ocean. Nature 421: 354-356.

Phadtare, N.R. and Pant, R.K. 2006. A century-scale pollen record of vegetation and climate history during the past 3500 years in the Pinder Valley, Kumaon Higher Himalaya, India. Journal of the Geological Society of India 68: 495-506.

von Rad, U., Michels, K.H., Schulz, H., Berger, W.H. and Sirocko, F. 1999. A 5000-yr record of climate change in varved sediments from the oxygen minimum zone off Pakistan, northeastern Arabian Sea. Quaternary Research 51: 39-53.

Reviewed 16 April 2008