Recent Accelerated Warming of the Laurentian Great Lake: A Regional Climate Modeling Study

Abstract:

The primary drivers of the recent accelerated warming of the Laurentian Great Lakes from 1982 to 2012 are explored through observations, remote sensing, and regional climate model experiments, focusing on the abrupt warming from 1997 to 1998 as a proxy of the long-term warming trend. The lake surface warming has been heterogeneous in both space and time, ranging from moderate warming over the southern lakes and shallow areas of the northern lakes, peaking in late spring, to strong warming over the northern, deep lake areas, peaking in mid-summer. The greatest lake warming between 1997 and 1998 occurs over the deepest areas of Lake Superior during mid-summer, primarily arising from enhanced heat accumulation during the mild 1997/1998 winter and amplified by greater solar radiation and air temperature during the spring of 1998. In contrast, the modest peak warming over southern lakes and shallow areas of northern lakes from 1997 to 1998 is a rapid response to synchronous increases in solar radiation and air temperature during May between the two years.

According to the model experiments, the reduction in surface albedo, attributed to diminished lake ice cover from the cold winter of 1996/1997 to the mild winter of 1997/1998, contributes to an earlier springtime termination of the lake ice season but leads to minimal impact on subsequent summertime lake temperatures. These results suggest that changes in antecedent wintertime lake ice cover have played only a minor role in the accelerated Great Lakes warming trend. Therefore, trends in lake ice cover can be viewed as a surrogate for changes in cumulative winter severity and not the key driver of summertime lake temperature warming.