Glaciers, Ice Caps Adding to Sea Levels

The good news? The massive ice sheets covering Greenland and Antarctica aren't expected to melt enough this century to raise sea levels substantially. The bad news? The globe's smaller ice caps and glaciers -- and there are many more of those -- are likely to release large volumes of meltwater into the world's oceans, according to a new study from the University of Colorado at Boulder (CU-Boulder).

Worldwide, glaciers and ice caps, which are smaller masses of land-based ice than the great sheets covering Greenland and Antarctica, account for about 60 percent of the ice now entering the oceans, the CU-Boulder researchers found. The rate at which those bodies of ice are entering the oceans has also been speeding up over the past 10 years. All combined, these bodies add about 100 cubic miles of ice a year to the oceans, and that rate is increasing by another three cubic miles each year.

By comparison, ice from Greenland accounts for about 28 percent of sea level rise caused by melting, while Antarctica's contribution is about 12 percent.

"One reason for this study is the widely held view that the Greenland and Antarctic ice sheets will be the principal causes of sea-level rise," said Mark Meier, lead author of the study and professor emeritus of CU-Boulder's Institute of Arctic and Alpine Research. "But we show that it is the glaciers and ice caps, not the two large ice sheets, that will be the big players in sea rise for at least the next few generations."

The contribution of glaciers and ice caps is speeding up because glaciers flow into the ocean more rapidly as they thin, according to Robert Anderson, a co-author of the study. In Alaska, for example, the Columbia Glacier has shrunk by around nine miles since 1980, and has thinned in sections by up to 1,300 feet. As a result, the glacier is now spilling some two cubic miles of ice into Prince William Sound every year.

"While this is a dynamic, complex process and does not seem to be a direct result of climate warming, it is likely that climate acts as a trigger to set off this dramatic response," Anderson said.