Journal Article

Spatial and temporal distribution of mass loss from the Greenland Ice Sheet since AD 1900

Funder, Svend, Willerslev, Eske, Nuth, Christopher, Bjørk, Anders A., Korsgaard, Niels J., Andresen, Camilla S., Box, Jason E., Kjær, Kurt H., Larsen, Nicolaj K., Schomacker, Anders, Kjeldsen, Kristian K., Bamber, Jonathan L., Siggaard-Andersen, Marie-Louise, Khan, Shfaqat A., van den Broeke, Michiel, Colgan, William

2015

Overview

Aerial imagery from the 1980s is used to calculate ice mass loss around the entire Greenland Ice Sheet from 1900 to the present; during the twentieth century the Greenland Ice Sheet contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Twentieth century Greenland ice loss The Greenland Ice Sheet (GIS) is losing mass at an accelerating rate, contributing to global sea level rise. But are the present rates unusual, compared to twentieth-century variability? It has been difficult to answer this question because of the shortage of observations before the late twentieth century. Kurt Kjær and colleagues address this data gap by analysing a collection of aerial photographs taken in the 1980s. The photos reveal both the maximum extent of the ice at the end of the Little Ice Age — from trimlines — and its position at the time the images were taken. The change is inferred by the difference. Incorporating this work with modern observations and models, the authors show that the Greenland Ice Sheet lost mass over the entire twentieth century, but that the recent rate of loss is more than double the earlier rates. Most of the accelerated loss has been caused by changes in surface mass balance, rather than through changes in the way the ice sheet is moving, which has remained approximately constant. The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious 1 , largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available 2 . The only previous estimates of change during the twentieth century are based on empirical modelling 3 , 4 , 5 and energy balance modelling 6 , 7 . Consequently, no observation-based estimates of the contribution from the GIS to the global-mean sea level budget before 1990 are included in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change 8 . Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age 9 at the end of the nineteenth century. We estimate the total ice mass loss and its spatial distribution for three periods: 1900–1983 (75.1 ± 29.4 gigatonnes per year), 1983–2003 (73.8 ± 40.5 gigatonnes per year), and 2003–2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models 10 , 11 we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term. We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years. Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget, which remains crucial for evaluating the reliability of models used to predict global sea level rise 1 , 8 .

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 20th century / 704/106/125 / 704/106/694 / Analysis / Climate change / Climate Change - statistics & numerical data / Climatic changes / Energy balance / Estimates / Glaciers / Greenland / History, 20th Century / History, 21st Century / Humanities and Social Sciences / Ice / Ice ages / Ice Cover / Ice sheets / Icebergs / Intergovernmental Panel on Climate Change / letter / Models, Theoretical / multidisciplinary / Observation / Photography / Reproducibility of Results / Science / Sea level / Sea level rise / Seawater - analysis / Spatial distribution / Spatio-Temporal Analysis / Sublimation / Temperature / Temporal distribution