Glaciers are direct recorders of climate history and have come to be regarded as emblematic of climate change. They respond to variations in both accumulation and ablation, which can have separate atmospheric controls, leading to some ambiguity in interpreting the causes of glacier changes. Both climate change and climate variability have characteristic spatial patterns and time scales. The focus of this study is the regional-scale response of glaciers to natural patterns of climate variability. Using the Pacific Northwest of North America as the setting, the authors employ a simple linear glacier model to study how the combination of patterns of melt-season temperature and patterns of annual accumulation produce patterns of glacier length variations. Regional-scale spatial correlations in glacier length variations reflect three factors: the spatial correlations in precipitation and melt-season temperature, the geometry of a glacier and how it determines the relative importance of temperature and precipitation, and the climatic setting of the glaciers (i.e., maritime or continental). With the self-consistent framework developed here, the authors are able to evaluate the relative importance of these three factors. The results also highlight that, in order to understand the natural variability of glaciers, it is critically important to know the small-scale patterns of climate in mountainous terrain. The method can be applied to any area containing mountain glaciers and provides a baseline expectation for natural glacier variation against which the effects of climate changes can be evaluated.