Climate warming has not resulted in measurable thawing of the cold (–5°C to –10°C) permafrost in northern Alaska during the last half century. The maximum depths of summer thaw at five locations near Barrow, Alaska, in 2005 were within the ranges of the depths obtained at those same locations during the early 1950s. However, there has been a net warming of about 2°C, after a cooling of 0.4°C during 1953–1960, at the upper depths of the permafrost column at two of the locations. Thawing of permafrost from above (increase in active layer thickness) is determined by the summer thawing index for the specific year; any warming, or cooling, of the upper permafrost column results from the cumulative effect of changes in the average annual air temperatures over a period of years, assuming no change in surface conditions. Theoretically, thawing from the base of permafrost should be negligible even in areas of thin (about 100–200 m) permafrost in northern Alaska. The reported shoreline erosion along the northern Alaska coast is a secondary result from changes in the adjacent ocean ice coverage during the fall stormy period, and is not directly because of any "thawing" of the permafrost.