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A Half-Century of Snow Cover Data from Western China
Reference
Dahe, Q., Shiyin, L. and Peiji, L. 2006. Snow cover distribution, variability, and response to climate change in western China. Journal of Climate 19: 1820-1833.

Background
The authors report that "the majority of the climatic community is convinced of a pronounced reduction in seasonal snow cover in response to CO2-induced global warming."

What was done
In a study designed to explore this belief, Dahe et al. examined spatial and temporal variabilities of snow cover in western China between 1951 and 1997, based on data obtained from the Scanning Multichannel Microwave Radiometer six-day snow-depth charts, National Oceanic and Atmospheric Administration weekly snow extent charts, and daily snow depth and number of snow cover days from 106 meteorological stations scattered across western China (27-50N, 70-105E), including its two major regions: northwestern China and the Qinghai-Xizang (Tibet) Plateau.

What was learned
Dahe et al.'s analysis revealed "a general and uniform positive trend of snow cover over western China." More specifically, over northwestern China, where "the snow season temperature fluctuated in a fairly similar manner as that of the global temperature," they found that "the long-term variability of snow cover is marked by a stochastic oscillation superimposed on a small increasing trend over the past 47 years." Even more strikingly, they report that "the annual cumulative daily snow depth increased by 2.3% per year [our italics] over the Qinghai-Xizang (Tibet) Plateau during the period between 1957 and 1998."

What it means
According to the scientists who conducted the study, "western China did not experience a continual decrease in annual snow storage and early disappearance of spring snow cover, even during the great warming periods of the 1980s and 1990s [our italics]." As a result, they say that "the increasing trend of western China snow cover is ... in contradiction to the regional warming."

In discussing their findings, the researchers note that "a persistent and misleading assertion is that global warming would decrease snow cover because snow cover has a strong negative relationship to temperature." In reality, they find that "snow cover trend is dependent on the snowfall trend rather than on the temperature trend, if winter temperature is well below freezing." In other words, as they continue, "even with global warming there is no reason for snow cover to decrease when snowfall is increasing and temperature is still to remain well below freezing in the region."

Reviewed 6 September 2006