Radar imaging shows loss of tundra lake ice

New research using satellite-based synthetic aperture radar imaging of the Alaska North Slope near Barrow shows that as the climate has warmed in recent decades fewer lakes have been freezing solid to the ground in the winter, according to a paper published in a recent issue of The Cryosphere by a team of researchers in Canada and Italy. By analyzing satellite imagery between 1991 and 2011 the researchers were able to show a progressive reduction in the amount of grounded ice, as distinct from floating ice, in late winter, with that reduction accelerating after 2006. A tendency towards thinning ice followed a similar trend.

The satellite data indicated a decrease of 22 percent in the fraction of lakes frozen to the bottom in April over the 20-year time span of the study. The highest percentage of lakes freezing completely, 62 percent, happened in 1992, while the lowest percentage of lakes with grounded ice, 26 percent, occurred in 2011.

Comparisons with actual measured lake ice thicknesses for some lakes in some years showed that the satellite-derived estimates were accurate within 4 percent.

A Canadian computer model that simulates lake-ice formation also predicted similar results to the results derived from satellite data. Using the rise in mean annual temperature and precipitation observed in recent decades this model also indicated the early winter lake freeze up becoming later by 5.9 days over the period 1950 to 2011, with the spring breakup of the ice coming 17.7 to 18.6 days earlier, depending on the snow cover, over that same timeframe.

—Alan Bailey