“It remains unclear if such losses will decline or will level off or will accelerate further," says Ian Joughin, a glaciologist at the University of Washington in Seattle. "The melting needs monitoring to further understand the ice sheet processes leading to the change.”
The findings show that two thirds of the annual ice loss is from the Greenland sheet. Indeed, Greenland is losing five times as much ice each year as it did in the 1990s.
Antarctica provides a more nuanced picture. In East Antarctica, which holds at least four-fifths of the continent’s ice, the mass ice forms are stable – actually gaining slightly during the past 20 years. But these gains are eclipsed by losses in West Antarctica and on the Antarctic peninsula, which yield a net loss of ice for the continent annually and account for the remaining third of total annual ice-sheet loss detailed in the study.
The report is a “milestone,” because it provides a more precise estimate of ice-sheet losses, the researchers said during a Wednesday teleconference. Previously, scientists had to sort through as many as 30 independent data estimates collected over 50 years, and these often produced the conflicting results, said Andrew Shepherd of the University of Leeds in Britain, a project leader.
The report also offers new clarity on sea-level rise. A 2007 report by the UN's Intergovernmental Panel on Climate Change (IPCC), for example, observed the reduction in size of the ice sheets, but was not conclusive about its effects on sea levels.