Glaciers are among the most trusted indicators of climate change, not just because they retreat due to the current rise in global temperatures but also because of their central role in reconstructing past climates. Glaciers come in many forms, and their sensitivity to climate change depends partly on the physics governing the individual glacier, implying that a response can be fast or slow, straightforward or complex, which in sum suggests that not all glaciers are equally suitable for reconstructing past and present climate conditions. In particular, surging and debris-covered glaciers may especially yield misleading results (Figure 1).