Sheet ice dynamics and glacial meltwater have been somewhat of a contentious issue in the past (link, read more). Mark Meier and colleagues from the Institute of Arctic and Alpine Research, University of Colorado have made the headlines in the journal Science magazine recently:

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. (link to full article)

As blogged on their website:

The team summarized satellite, aircraft and ground-based data from glaciers, ice caps, the Greenland ice sheet, the West Antarctic ice sheet and the East Antarctic ice sheet to calculate present and future rates of ice loss. They concluded that glaciers and ice caps are currently contributing about 60 percent of the ice delivered to the world’s oceans and the rate has been markedly accelerating in the past decade. The contribution is presently about 100 cubic miles of ice annually — a volume nearly equal to the water in Lake Erie — and is rising by about three cubic miles per year. The accelerating contribution of glaciers and ice caps is due in part to increased meltwater at the ice surface. Some glaciers are also experiencing increased meltwater at the base of the ice, which can lead to faster sliding of the glaciers against their beds.

This is especially the case for tidewater glaciers that discharge icebergs directly into the ocean, and their analogs, the outlet glaciers from the great ice sheets. Many tidewater glaciers are undergoing rapid thinning, stretching and retreat, which in turn causes them to speed up and deliver increased amounts of ice into the world’s oceans.