Ice loss to the sea currently accounts for virtually all of the sea-level rise that is not attributable to ocean warming, and about 60% of the ice loss is from glaciers and ice caps rather than from the two ice sheets. The contribution of these smaller glaciers has accelerated over the past decade, in part due to marked thinning and retreat of marine-terminating glaciers associated with a dynamic instability that is generally not considered in mass-balance and climate modeling. This acceleration of glacier melt may cause 0.1 to 0.25 meter of additional sea-level rise by 2100.

The microstructure of snow and firn controls the transport of chemical species from the atmosphere into and out of the underlying firn. Permeability and thick-section microstructure measurements have been made from snow-pit and firn-core samples retrieved near the proposed deep-drilling site for the inland West Antarctic ice sheet. Measurements in past investigations of polar firn show that the permeability of the snow gradually increases with depth into the core to about 2 m, then decreases. In this core, there is a second maximum in permeability at approximately 12 m that is likely due to changes in meteorological conditions at the site. Either lower temperatures or higher accumulation rates in the most recent three to four decades could cause the changes in microstructure and permeability in this core. We suggest that climate shifts may alter gas records ultimately preserved in the ice because of the local climate’s effect on the permeability profile.