AbstractThe recent article by Schoof (J. Fluid Mech., vol. 712, 2012, pp. 552–578) provides a technically demanding solution to the problem of determining ice-stream margin evolution. It is important in opening the way to the future theoretical description of how the ice sheets will melt and sea level will rise as the climate warms. But the sophistication of the mathematics should not operate as a mask to an examination of the credibility of the model.