没有直接的方法来确定过去的冰厚度。唯一存在的可靠信息是过去的区域范围。但是，即使这些信息也不一定清楚，因为后来的进展可能已经覆盖了过去的终端位置，日期也可能不准确。一个主要的问题是所有这些位置的同步性。在过去的一定程度上，有可能根据我们对冰物理和动力学的理解来校准数值冰盖模型，并生成可能的冰盖配置。这样的模型生成一个三维冰原，其中包括冰的厚度。从本质上说，这是估计过去冰层厚度的最佳方案。先进的模型还包括某种形式的均衡，取决于覆盖的冰荷载。对于上一次最大冰期，回弹值也被用来约束冰盖的几何形状。然而，问题是，地壳对加载的响应取决于加载历史，在不同的情况下可能会得到类似的结果，因为地壳的凹陷部分是加载的，但也是加载的时间尺度。 For a long time we though the latest glaciation was one long period of glaciation but we now know that, at least the Fennoscandian ice sheet, experienced two major advances, the mid-Weichselian and the Last Glacial maximum and both were relatively short in duration. This allows us to modify the loading history of the latest glacation. With the earlier glaciations, we do not yet have such detailed loading histories and are thus not able to make detailed models of ice thickness. It should be added the the understanding of the variations of the last ice sheet come from a series of indirect sources such as sea-level changes, paleo-climate records e.g., (ice cores) and interstadial paleoclimate reconstructions. This means that as our understanding of these indirect records are improved, we can also improve our ice sheet forcing. Add to that uncertainties about basal conditions beneath past ice sheets that affect their dynamics and it is easy to see that past ice thickness values are uncertain. We can, however, obtain reasonable estimates from the models which could be accurate to within, perhaps 500 m (my guestimate).