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thawing indices. The warmer boundary of the zone of continuous permafrost traverses the mean annual air temperature (MAAT). The boundary between discontinuous and sporadic permafrost lies just on the cold side of 0°C MAAT. The sporadic permafrost zone includes the zone of ice caves and the regions with patches of ice beneath ponds and peatbogs, extending to 5°C MAAT at a thawing index of 4000
degree days per year. The relationship is applicable to Norway, Iceland, Spitzbergen, Canada and the People’s Republic of Mongolia.
There are some marked variations in lapse rate from one environment to another, them ost marked of which occurs above tree line where the lapse rate increases markedly in winter, though not in summer. This produces a change in MAAT of 23°C on Plateau Mountain. The changes also occur at some points in non-permafrost areas and it appears likely that they are due to spatial and seasonal changes in albedo.
Whatever the cause, the variations in lapse rate indicate that calculations of past world climatic change based on data from one aream ay be misleading.