Watch Out for Your Neighborhood Glacier!
13 Sep, 2007 01:41 pm
Ice loss from glaciers and ice caps is expected to cause more global sea level rise during this century than the Greenland and Antarctic ice sheets (Meier and others, 2007).
The accelerating melt of glaciers and ice caps could add from 4 inches to 9.5 inches of additional sea-level rise globally by 2100. This does not include the expansion of warming ocean water, which could potentially double those numbers. A one-foot sea-level rise typically causes a shoreline retreat of 100 feet or more, and about 100 million people now live within about three feet of sea level.
Ice loss to the ocean can occur by melt and subsequent flow to the oceans, and from direct discharge into the oceans by iceberg calving. The current acceleration in ice loss is due in part to an increase in this latter effect. There have been rapid changes in the flow of tidewater glaciers that discharge icebergs directly into the ocean, and many tidewater glaciers are undergoing rapid thinning, stretching and retreat, which cause them to speed up and deliver even more ice to the ocean. In addition to direct ice loss through flow of meltwater to the ocean, an increase in the melting of ice can also have an affect on glacier speed. Water controls how rapidly glaciers slide along their beds, and when a tidewater glacier thins, a larger fraction of its weight is supported by water and it slides faster and calves more ice into the ocean at the glacier terminus.
Alaska's Columbia Glacier, which is now discharging about two cubic miles of ice annually into Prince William Sound, is a good example of a tidewater glacier undergoing rapid changes. The Columbia Glacier, which has thinned up to 1,300 feet in places, has shrunk by about nine miles since 1980 and is expected to shrink by another nine miles in the next two decades. Outlet glaciers in Greenland may behave much like tidewater glaciers in Canada and Alaska, making North American glaciers relevant for long-term ice loss studies.
We 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 for the study. We then used a mathematical "scaling" process to estimate more remote glacier volumes, thicknesses and trends by factoring in data like altitude, climate and geography. The data was gathered from around the world, including cold regions in Russia, Europe, China, Central Asia, Canada and South America. There are several hundred thousand small glaciers and small, pancake-shaped ice caps in polar and temperate regions. They range from modest, high mountain glaciers to huge glaciers like the Bering Glacier in Alaska, which measures about 5,000 square miles in area and is nearly one-half mile thick in places.
While warming temperatures will likely cause many small high mountain glaciers in North America and Europe to disappear by the end of the century, large ice fields and ice caps will continue to produce large amounts of meltwater. The retreat of the Greenland and Antarctic ice sheets also is giving rise to new, smaller glaciers that are prime candidates for further study. It is incorrect to say that small glaciers will disappear and become unimportant to sea level rise. They will continue to play a key role in the sea level story.
Meier F. M., et al, Glaciers Dominate Eustatic Sea-Level Rise in the 21st Century, Science, August 24