4.7.3.3 Near-Surface Soil Freeze-Thaw Cycle

Satellite remote sensing data have been used to detect the near-surface soil freeze-thaw cycle at regional and hemispheric scales. Evidence from the satellite record indicates that the onset dates of thaw in spring and freeze in autumn advanced five to seven days in Eurasia over the period 1988 to 2002, leading to an earlier start to the growing season but no change in its length (Smith et al., 2004). In North America, a trend towards later freeze dates in autumn by about five days led, in part, to a lengthening of the growing season by eight days. Overall, the timing of seasonal thawing and subsequent initiation of the growing season in early spring has advanced by approximately eight days from 1988 to 2001 for the pan-arctic basin and Alaska (McDonald et al., 2004).