Climate Bifurcations in a Schwarzschild Equation Model of the Arctic Atmosphere

Speaker:  Allan Willms (Guelph)

Abstract:  We present a column model of the Arctic atmosphere that incorporates radiation flux governed by the two-stream Schwarzschild equations, water vapor concentrations governed by the Clausius-Clapeyron equation and nonlinear surface albedo response to temperature.  Representative carbon pathways (RCPs) are used to model carbon dioxide concentrations into the future.  The resulting nine-dimensional two-point boundary value problem is solved and various RCPs are applied to the solutions.  The model predicts that under the highest carbon pathway, the Arctic climate will undergo an irreversible bifurcation to a warm steady state, which would correspond to an annually ice-free situation.  Under the lowest carbon pathway, corresponding to very aggressive carbon emission reductions, the model exhibits only a mild increase in Arctic temperatures.  Under the two moderate carbon pathways, temperatures increase more substantially, and the system enters a region of bistability where external perturbations could possibly cause an irreversible switch to a warm, ice-free state.