The need for global glacier speed to combine measured velocity with balance velocity

One of the outstanding glaciological research questions is how glaciers respond dynamically to climate change and how this varies regionally. Ice-velocity changes occur on an interannual scale in response to mass-balance forcing changing the glacier geometry and therefore the driving stress. For a glacier tending towards steady-state the mass flux through a cross-section equals the mass balance upstream of the cross-section. Mass loss will, therefore, usually lead to a slowdown of glaciers. However, a changing climate can also affect the occurrence of sliding and change a glacier’s thermal regime and its marginal processes (ice-ocean, ice-lake and ice-bed interactions). The response of glacier flow to climate change is, therefore, not straightforward, and mass loss combined with increased meltwater production or a transition to a temperate regime may lead to an increase in flow speed. Ultimately, depending on their individual response time, glaciers respond in a delayed dynamical way to changes in mass balance.

Various recent publications have addressed the above research question at regional scales by analysing decadal changes in flow speed in relation to glacier mass loss. Only few local works, however, have addressed the question in the context of measured differences between actual and balance velocities. The recent generation of diverse global glacier datasets, such as the Randolph Glacier Inventory (RGI), GoLIVE and ITS_LIVE ice speed, ice thickness, and globally-distributed datasets such as WGMS mass balance data and companion ground measurements, offer opportunities to address outstanding research questions in interregional to global perspectives. We will compare, for the first time, for glaciers in various RGI subregions the difference between the measured glacier velocity, derived from available GoLIVE and ITS-LIVE datasets and additional speckle tracking from SAR scenes, and the balance velocity, derived using mass balance profiles, hypsometry, and ice thickness datasets. We use the standard approach of deriving balance flux along a flowline, and use a scenario-based approach to deal with measurement and model uncertainties. In this poster we present the results for approximately 20 glaciers in Canada and Iceland in detail. Ultimately, we aim to use more than 200 glaciers with WGMS and independent long-term mass balance records, distributed over the 19 RGI first-order regions and as many as the 89 second-order regions as possible.