While they are at it, they should try to quantify the so-called ‘buttressing effect,’ which I think is overestimated. Glacier advance is a complex function of the type of bedrock, the relief of the topography, whether liquid water is present or not, the thickness of the ice, and the average slope of the glacial bed. Whether moraines have any substantial influence on the speed of forward motion is debatable because we know (and the authors acknowledge) that glaciers can bulldoze their way through an unconsolidated moraine. If something like a high bedrock ridge or submarine dike is present, it will provide a more challenging obstacle. However, if the ice is thick enough to be flowing plastically, it is likely to just shear over the top of the obstacle; in that case, the advance will be controlled by the shearing velocity.

Glaciers, or rather the ice of which they are composed, are always advancing, except in the waning stages of glaciation, when the ice may become stagnant. What the above quote is referring to is the front, or terminus, moving forward when the rate of ice movement is greater than the rate of ablation. When the terminus is fixed, the till carried by the ice piles up to make a moraine. A glacier can and will destroy its own terminal moraine if the front is advancing. For that reason, the terminal moraine (paleo-moraine) is usually interpreted as being the maximum distance the ice has reached. Intermediate moraines are positions where the terminus was temporarily fixed and the ablation rate was equal to the advance rate.

More importantly, warm ocean waters can attack the ice when it is in the ocean. If the terminus recedes to where it is above the water line, then that can no longer happen. Thus, there will be an abrupt decrease in the rate of ablation, or melting. Any projections of future melting will be much too high if it is based on a linear projection of current melting rates and does not take into account sea level. Indeed, they really need to take into account the depth of the water leading up to that condition because if the ice is not floating the water cannot effectively melt the underside of the ice; it will only be able to melt the leading edge.

It doesn’t give me a warm fuzzy feeling that these researchers know what they are doing when their description of glaciation is so simplistic as to be wrong.