What was done
Chen et al. studied the chemical composition of sediments deposited in Lake Erhai (25°35'-25°58'N, 100°05'-100°17'E), which is the largest fault lake in the western Yunnan Province of China.  More specifically, they applied Principal Component Analysis to the concentrations of 21 major and minor elements found in the sediments, thereby deriving historical variations in temperature and precipitation over the period AD 1340-1990.

What was learned
The authors' work revealed an initial period (1340-1550) of relatively high temperature and low rainfall.  Thereafter, the climate gradually become cooler and wetter, coincident with the development of the Little Ice Age, which lasted until about 1890.  Then, from 1890 to 1950, another warm and dry period held sway, followed by a cooling since the end of the 1940s.

What it means
Defined by the contrast it presents to the warmer periods that preceded and followed it, the presence of the Little Ice Age in the western Yunan Province of China is clearly demonstrated by the results of this study.  Of even more interest, however, is the fact that the warmest temperatures of the past six and a half centuries in this part of the world occurred during what we have called the Little Medieval Warm Period, about which one can read more in our Subject Index.  In addition, it is important to note that the Lake Erhai region has been cooling for the past half-century.  All three of these observations are at odds with the hockeystick temperature history of Mann et al. (1998, 1999).

References
Mann, M.E., Bradley, R.S. and Hughes, M.K.  1998.  Global-scale temperature patterns and climate forcing over the past six centuries.  Nature 392: 779-787.

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.