Yadav, R.R., Park, W.K., Singh, J. and Dubey, B. 2004. Do the western Himalayas defy global warming? Geophysical Research Letters 31: 10.1029/2004GL020201.
What was done
Many long tree-ring series obtained from widely-spaced Himalayan cedar (Cedrus deodara (Roxb.) G. Don) trees growing on steep slopes with thin soil cover were used to develop a temperature history of the western Himalayas for the period AD 1226-2000.
What was learned
"Since the 16th century," in the words of the authors, "the reconstructed temperature shows higher variability as compared to the earlier part of the series (AD 1226-1500), reflecting unstable climate during the Little Ice Age (LIA)." With respect to this greater variability of climate during colder conditions, they note that similar results have been obtained from juniper tree-ring chronologies from central Tibet (Braeuning, 2001), and that "historical records on the frequency of droughts, dust storms and floods in China also show that the climate during the LIA was highly unstable (Zhang and Crowley, 1989)."
As for temperature itself, Yadav et al. report that 1944-1953 was the warmest 10-year mean of the entire 775-year record, and that "thereafter, temperatures decreased." With respect to this cooling, they note that it "is in agreement with the instrumental records." Also, they state that "tree-ring based temperature reconstructions from other Asian mountain regions like Nepal (Cook et al., 2003), Tibet and central Asia (Briffa et al., 2001) also document cooling during [the] last decades of the 20th century." In fact, the temperatures of the final two decades of Yadav et al.'s record appear to be as cold as those of any comparable period over the prior seven and a half centuries, including the coldest periods of the Little Ice Age, which result, as they indicate, is radically different from the temperature reconstruction of Mann and Jones (2003) that depicts "unprecedented warming in the 20th century."
What it means
First of all, for this and many other parts of the world, higher temperatures, such as those of the Medieval Warm Period, generally lead to much more stable climatic conditions, with fewer droughts and floods, than do colder temperatures, such as those of the Little Ice Age, which finding suggests that warming does not produce more numerous and intense weather extremes, in contradiction of one of the most fundamental of all climate-alarmist claims. Second, for some pretty large portions of the planet -- if not all of it, in the mean -- the last few decades of the 20th century have not been anomalously warm, as climate alarmists are also prone to claim.
Braeuning, A. 2001. Climate history of Tibetan Plateau during the last 1000 years derived from a network of juniper chronologies. Dendrochronologia 19: 127-137.
Briffa, K.R., Osborn, T.J., Schweingruber, F.H., Harris, I.C., Jones, P.D., Shiyatov, S.G. and Vaganov, E.A. 2001. Low frequency temperature variations from northern tree ring density network. Journal of Geophysical Research 106: 2929-2941.
Cook, E.R., Krusic, P.J. and Jones, P.D. 2003. Dendroclimatic signals in long tree-ring chronologies from the Himalayas of Nepal. International Journal of Climatology 23: 707-732.
Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.
Zhang, J. and Crowley, T.J. 1989. Historical climate records in China and reconstruction of past climates (1470-1970). Journal of Climate 2: 833-849.
Reviewed 29 September 2004