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A 400-Year Climatic History of the Western Himalayan Region of India
Yadav, R.R. and Singh, J. 2002. Tree-ring-based spring temperature patterns over the past four centuries in western Himalaya. Quaternary Research 57: 299-305.

What was done
The authors developed a spring (March-May) temperature reconstruction for the western Himalayan region of India (approximately 30.5-31N, 78.7-79.7E) based on a network of twelve tree-ring chronologies of Himalayan cedar (Cedrus deodara (D. Don) G. Don). In addition, since "spring temperature is significantly correlated with mean annual temperature (r = 0.7, p < 0.0001)," as noted by the authors, they say "the reconstruction to some extent reflects the general temperature variations over the Himalayan region."

What was learned
In the words of the authors, "the most conspicuous feature of the temperature reconstruction is the long-term cooling trend since the late 17th century that ended early in the 20th century." The abrupt termination of this cooling, which heralded the end of the Little Ice Age, soon thereafter produced the warmest 30-year period of the 20th century (1945-1974). This warm interval, however, was "well within the range of natural variability," as the authors describe it. In fact, there was an even warmer 30-year period in the latter part of the 17th century (1662-1691).

In comparing their temperature reconstruction with that of Mann et al. (1999), the authors report there was no correlation between the two temperature histories prior to the 20th century. Another discrepancy begins where both tree-ring reconstructions end. Whereas the instrumental record reported by Mann et al. indicates dramatic warming over the last two decades of the 20th century, the instrumental record reported by Yadav and Singh indicates cooling, as is also indicated by several other papers they cite that are based on both instrumental and tree-ring observations.

What it means
As more and more data become available - see also Esper et al. (2002a, 2002b) - the Mann et al. "hockey stick" curve is beginning to look more and more suspect, both in terms of its long-term historical reconstruction and the last two decades of instrumental observations.

Esper, J., Cook, E.R. and Schweingruber, F.H. 2002a. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science 295: 2250-2253.

Esper, J., Schweingruber, F.H. and Winiger, M. 2002b. 1300 years of climatic history for Western Central Asia inferred from tree-rings. The Holocene 12: 267-277.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.

Reviewed 29 May 2002