There are many definitions for the phrase ‘Cold Regions’, albeit it has been widely used.

In China, Cold Regions should include all the permafrost area, the glacier area, and the great majority of stable seasonal snow cover area, in which the vegetation type and climate type are, to some extent, unique compared with those in the other regions. The air temperature, according to the literal meaning of ‘Cold Regions’, is the major factor to judge whether a region belongs to Cold Regions or not. In this essay, the averaged monthly air temperature data, which were derived from 4-time daily data, at the 571 stations in China, from 1961 to 1998, were used.

The averaged monthly air temperature at the each 1 km grid in Alberts projection was calculated by using the regressing equation, in which altitude, Y axis and X axis in Alberts projection of the 571 stations were input and R2 was of 0.92–0.97. The results show that the Woo's definition and Yang's definition for the Cold Regions are not appropriate in China. A new definition of the Cold Regions in China should be that the averaged air temperature of the coldest month is lower than − 3.0 °C, the number of months of which the averaged air temperature is higher than 10 °C is not more than 5, and the averaged yearly temperature does not exceed 5.0 °C. The new partition by the definition is nearly in accordance with the borders of the defacto area of permafrost, seasonal stable snow cover, vegetation distribution and climate regionalization. Therefore, the area of the Cold Regions in China by the new definition is about 417.4 × 104 km2, 43.5% of the country's land area.

The permafrost area is about 25% of land area in the Earth (Zhou et al., 2000), while the cold regions are distributed more widely. In China, the permafrost area is about 215 × 104 km2 (Yang and Zeng, 2001), the glacier area is about 59406 km2 (Yang, 1991 and Yang et al., 2000), and the stable seasonal snow cover area (the area where snow covers at least 60 days in a year) is about 230 × 104 km2 (Li, 1983). Cold Regions in China, with relative abundance of solid and liquid precipitation, are the primary headsprings of water resources for the arid and semiarid regions in China (Yang et al., 2000). Moreover, many engineering must be constructed in the Cold Regions. However, Cold Regions are very sensitive to global changes (Li and Guodong, 1999 and Li et al., 2003a), which makes it necessary to take the Cold Regions as a research unit, to study the variations of permafrost distribution, snow depth, snow cover and glacier distribution, and to analyze the reciprocal relationship between climate system and environment.

The phrase ‘Cold Regions’ often appears in the literature and in the media (e.g. Feng et al., 2003, Xie et al., 2003 and Cheng et al., 2004 F. Cheng, H.X. Zhang, Y. Yu, G.H. Xu, X.Y. Liu and C.M. Qi, Weathering crust and placer gold in cold regions of Northeast China, Journal of Glaciology and Geocryology 26 (2004) (2), pp. 219–223 (in Chinese).Cheng et al., 2004). However, there is no unified definition for it. Köppen (1936) made the first definition for the northern cold regions in Canada as that, the averaged air temperature of the coldest month was not higher than − 3.0 °C, and the number of months of which the averaged air temperature was higher than 10 °C was not more than 4.

 Perhaps the broadest and simplest coldness definition of the northern cold regions in Canada was that by Gerdel (1969) who used the 0 °C mean annual isotherm of the coldest month as the southern limit. This, however, results in a North extending as far south as latitude 36°N. Combining air temperature and precipitation factors should provide a better hydrological definition of the North in Canada (Wilson, 1967). It results in a southern limit of the cold, northern regions being approximately between 50°N and 55°N. Apparently, the precipitation factor is not that significant since the boundary closely parallels that of the southern limit of the Subarctic, a simple temperature-based definition. Hamelin (1979) defined the northern cold regions in Canada by combining 10 factors. However, it meets great difficulty in picturing the area for its geographic immensity. Yang (1997) firstly used the Woo's (Woo, 1996) definition for North America to classify the Cold Regions in China: a mean air temperature of the coldest month lower than − 3 °C, no more than 4 months with a mean air temperature higher than 10 °C, more than 100 days of freezing rivers or lakes, and with solid precipitation higher than 50% in a year. However, the condition in China is different from that of in Canada, considering the geographical position, topography, environment and climate. In this case, Yang et al. (2000) took for that the Woo's classification is not appropriate in China, and gave 10 climate factors to define the Cold Regions in China