To Chris Reynolds' point: I disagree to a certain extent that we can apply the Thorndike paper directly to the ice situation. This is constructed for ice freeze-up with a certain surface temperature. This means that an arbitrary heat flux can be applied to the surface to provide those conditions. However, when a water surface of the size of the Arctic Ocean is ice-free, the heat flux is limited by a) radiation into space and b) lateral heat flow in atmosphere and ocean. So we should rather ask if the heat accumulation in Summer might get the Arctic through the winter or most of the winter.