There is a perception that climatic warming was the cause of the twentieth-century global warming and thawing of permafrost and associated terrain instability (thermokarst) [Gore, 2006; Perkins, 2007; Zielinski, 2007; Delisle, 2007]. While pertinent data are sparse, published results do not support this viewpoint [Zhang et al., 2001; Osterkamp, 2007]. This brief report reviews the warming of permafrost in Alaska during the twentieth century and shows that snow cover has played a significant role in it.

Air temperatures in Alaska increased from the late 1800s until the early 1940s and decreased during the third quarter of the century. While the long-term data are sparse, snow cover appears to have increased during the third quarter. Air temperatures increased sharply (1°–2°C) at the start of the fourth quarter, but trends to the end of the century were variable. Some sites warmed while others showed little or no warming or a cooling.