Previous studies which have applied the output of general circulation models (GCMs) to a model of the hydrology of the Laurentian Great Lakes drainage system have shown decreased net basin supplies and lowered water levels, with one exception–the recent study which used the results of the Hadley Centre Model, version 2 (HadCM2). The present study is qualitatively in agreement with this exception–the results of a regional climate model (Coupled Hydrosphere-Atmosphere Research Model or CHARM) show a 132% increase in net basin supply for the Lake Superior drainage basin in a 9-year period centered at 2095 relative to one centered about 1989, assuming a 1% compounded annual increase in atmospheric CO₂ concentration. The net basin supply over the Lake Michigan basin increased by 59% and the Lake Erie net basin supply increased by 82%. A major factor that is common between HadCM2 and CHARM that distinguishes them from the other GCMs is the presence of the Great Lakes, at least idealized as large rectangular grid boxes, as agents to moisten the planetary boundary layer and thus inhibit evaporation.

Due to increased liquid precipitation during the winter and earlier snowmelt in the cases with enhanced greenhouse gas concentrations, the spring maximum in runoff in the 2095 case is less prominent and is shifted to earlier in the year. One deficiency that remains in this model is that wintertime temperatures have a warm bias during the winter in the 1989 case, and therefore they have relatively little lake ice cover. This may unrealistically reduce the sensitivity of wintertime evaporation from the lakes due to reductions in ice cover.