Causes of warming and thawing permafrost in Alaska

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.