Recent temperature history of the Juneau Icefield

Recent temperature history of the Juneau Icefield

 

Mass loss from Alaskan glaciers makes a significant contribution to current sea-level rise. The Juneau Icefield (JIF) of southeast Alaska is one of the world largest, and longest-studied, ice fields, and is currently in a documented state of thinning, retreat, and negative mass balance. The climatological context of this glacier change is critical to understanding its causes, the future of the region, and perhaps that of similar mountain glaciers. Do these changes primarily reflect changes in accumulation or ablation? Are mean air temperatures in the region increasing? If so, during which season, ablation or accumulation, are the changes strongest?

Here we investigate the recent temperature history of the Juneau Icefield, using a combination of reanalysis data and in situ temperature observations from the Juneau Icefield Research Program.  On the whole, we find a significant trend in annual average temperature since the 1950’s of 0.19°C per decade. Interestingly, this warming is entirely a winter-season signal. We find no significant trend in summer-season temperatures, but a winter time trend of nearly 0.5°C per decade, over twice that of the annual average. This pattern is consistent between the reanalysis products and the local temperature observations across the icefield. Using the in situ measurements from stations across the icefield, we find that the magnitude of the winter-season warming (and that of the annual mean warming) depends strongly on surface elevation: the higher the surface elevation the larger the trend in warming. These results have implications for the cause of recent glacier changes. While there is little evidence for a change in ablation-season temperatures, these results point toward changes in both the length of the ablation season and perhaps the phase of winter precipitation. The elevation-dependence of these trends may have further implications for the future stability of the JIF.