Elucidating the Primary Mechanisms Responsible for the Rapid Warming of the Laurentian Great Lakes
Elucidating the Primary Mechanisms Responsible for the Rapid Warming of the Laurentian Great Lakes
Previously Published Material: We have not written a publication on these results yet. We presented the results at the 2014 AGU Fall Meeting. We were invited to submit an abstract for an invited talk by John Lenters.
Abstract ID#: 33480
English Abstract:
During the last three decades, the Laurentian Great Lakes have exhibited rapid warming, particularly the deep portions of Lakes Superior and Michigan. The fact that the lakes are warming more rapidly than air over nearby coastal regions is counterintuitive from the simple perspective of heat capacity. The summertime lake warming is characterized by a distinct step function jump between 1997 and 1998. The currently accepted paradigm for this rapid lake warming is the ice albedo feedback, triggered by a rapid decline in lake ice cover since the late 1970s. Here, we challenge this paradigm through the application of a high-resolution regional climate model, focusing specifically on the 1997-1998 transition as the primary cause for the long-term lake temperature trend. Through a series of carefully designed manipulation experiments, we decompose the relative contribution of antecedent wintertime lake conditions (e.g. lake temperatures, ice cover) versus synchronous, springtime-to-summertime large-scale meteorological forcings (e.g. air temperature, solar radiation) towards the abrupt lake warming from 1997 to 1998. Both the long-term trend (1979-pres.) and 1997-1998 transition are characterized by positive trends in 500-hPa heights, air temperatures, and solar radiation and negative trends in cloud cover during spring-summer across the basin. Over the deep lake areas, the amplified summertime warming of the lakes, compared to air, is largely attributed to antecedent warming of the wintertime lake temperatures and their subsequent support for earlier lake stratification. In contrast, the warming of shallow lake areas is primarily in response to large-scale meteorological drivers during spring-summer, namely greater solar radiation and air temperatures. Changes in winter-spring ice cover between 1997 and 1998 produce minimal impacts on the timing of lake stratification or subsequent summer lake temperatures, thereby challenging the existing ice albedo paradigm.