Department of Earth System Science

Summary: The vast polar ice sheets are shrinking as our climate becomes warmer. Floating ice shelves and glacier tongues are thinning and even breaking up in both Greenland and Antarctica, probably because of the combined effects of warming ocean waters and increasing summer air temperatures. Much of this floating ice fills coastal embayments, and is pushed seawards by tributary glaciers, which are observed to accelerate, as much as eightfold, following ice-shelf break-up. At the same time, warmer summers are extending the zone and intensity of summer melting to higher elevations, particularly in Greenland. This increases both meltwater runoff into the ocean and meltwater drainage to the bed, where it lubricates glacier sliding and potentially increases ice discharge into the ocean.

Together these changes have resulted in net losses from both ice sheets at rates that are increasing with time. Corresponding sea-level rise increased from about 0.2 mm per year in the early 1990s to perhaps 0.8 mm per year since 2003, contributing to the total observed rise during the 1990s of approximately 3 mm per year. Some of the thinning glaciers extend many tens to hundreds of kilometres inland, and whether or not ice losses continue to accelerate will depend partly on whether ice shelves continue to thin, and partly on how far inland the zones of glacier acceleration can extend. These questions represent a major challenge to scientists, and their answers could have a profound impact on all of us. Research planned for the International Polar Year in 2007-2008 aims to answer them.