Oceanography (Jun 2011)
Land Ice and Sea Level Rise: A Thirty-Year Perspective
Abstract
The present-day assessment of contributions to sea level rise from glaciers and ice sheets depends to a large degree on new technologies that allow efficient and precise detection of change in otherwise inaccessible polar regions. The creation of an overall research strategy, however, was set in early collaborative efforts nearly 30 years ago to assess and project the contributions of glaciers and ice sheets to sea level rise. Many of the research objectives recommended by those early collaborations were followed by highly successful research programs and led to significant accomplishments. Other objectives are still being pursued, with significant intermediate results, but have yet to mature into fully operational tools; among them is the fully deterministic numerical ice sheet model. Recognized as a crucial tool in 1983 by the first formal working group to be convened to quantitatively evaluate glaciers and ice sheet contributions to sea level in a CO2-warmed future environment, the deterministic numerical model of glacier and ice sheet behavior has been the ultimate prognostic tool sought by the glaciological research community ever since. Progress toward this goal has been thwarted, however, by lack of knowledge of certain physical processes, especially those associated with interactions of ice with the bedrock it rests on, and interactions of ice with the ocean and calving of icebergs. Over the last decade, when mass loss rates from Greenland and Antarctica started to accelerate, some means of projecting glacier and ice sheet changes became increasingly necessary, and alternatives to deterministic numerical models were sought. The result was a variety of extrapolation schemes that offer partial constraints on future glacier and ice sheet losses, but also contain significant uncertainties and rely on assumptions that are not always clearly expressed. This review examines the history of assessments of glacier and ice sheet contributions to sea level rise, and considers how questions asked 30 years ago shaped the nature of the research agenda being carried out today.
