Interannual climate variability helps define the mean state of glaciers

Changes in glacier length and extent are indicators of contemporary and archives of past climate changes, but this common climate proxy presents a challenge for inferring a climate signal. Modeling studies suggest that length fluctuations can occur due to interannual climate variability within an unchanging mean climate and that changes in interannual climate variability can also drive changes in average length. This paper quantifies the impacts of interannual climate variability on average glacier length and mass balance, using a flowline model coupled to a simplified mass-balance model. Results illustrate that changes in the magnitude of interannual temperature variability can non-linearly affect the mean glacier length through a mass-balance asymmetry between warm and cold years. This asymmetry is present in models where melt only initiates after a temperature threshold is crossed. Glaciers susceptible to this asymmetry can be identified based on the shape of their mass-balance profiles. The presence of mass-balance asymmetries in glaciological databases is evaluated, but current records are too short for high statistical resolving power. While the asymmetry in this study can affect the average length and mass-balance, its impacts are small, and paleoclimate interpretations from glacier-length changes are likely not notably influenced by this process.