Contribution of the Greenland and An-tarctica Ice Sheets to Future Sea-level Rise

In recent years, the rates of thinning and flow of ice sheet<!–[if supportFields]>XE “ice sheet”<![endif]–><!–[if supportFields]><![endif]–>s have been increasing rapidly all around the world. Typically, researchers use surface mass balance estimates to measure this mass loss and predict future trends in ice sheet mass balance. However, Rignot et al. (2011) claim that surface mass balance calculations do not accurately represent the ice sheet’s contribution to sea level rise. In their paper, the authors used the rate of change of mass loss coupled with surface mass balance calculations to study the contribution of the ice sheets of Greenland and Antarctica<!–[if supportFields]> XE “Antarctica” <![endif]–><!–[if supportFields]><![endif]–> to sea-level rise<!–[if supportFields]> XE “sea-level rise (SLR)” <![endif]–><!–[if supportFields]><![endif]–>. Their results revealed that over the last 8 years, the Greenland and Antarctica ice sheet loss has accelerated by 36.3 ± 2 Gt/yr, 3 times more than the acceleration from mountain glaciers<!–[if supportFields]> XE “glaciers” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “glacier” <![endif]–><!–[if supportFields]><![endif]–> and icecaps. Given the magnitude of this acceleration, the authors conclude that ice sheets will be the major contributor to sea-level rise in the 21st century. —Sachi Singh
Rignot, E., I. Velicogna, M. R.van den Broeke, A. Monaghan, and J. Lenaerts. 2011. Acceleration of the contribution of the Greenland and Antarctic<!–[if supportFields]> XE “Antarctic” <![endif]–><!–[if supportFields]><![endif]–> ice sheet<!–[if supportFields]> XE “ice sheet” <![endif]–><!–[if supportFields]><![endif]–>s to sea level rise, Geophys. Res. Lett., 38, L05503, doi:10.1029/2011GL046583

Multi-decadal mass balance observations are required to estimate long term trends in ice sheet<!–[if supportFields]> XE “ice sheet” <![endif]–><!–[if supportFields]><![endif]–> mass balance. While the mass balance estimates have improved significantly in the last decade, they are not sufficient to predict the non-linear contributions of the ice sheet to rise in sea-level. In this paper, the authors used the mass budget method (MBM) and the gravity method to estimate the temporal variations in the mass balance of the Greenland and Antarctica<!–[if supportFields]>XE “Antarctica” <![endif]–><!–[if supportFields]><![endif]–> ice sheets. The MBM calculates the ice sheet’s rate of mass change by comparing the surface mass balance from regional atmospheric models to the ice discharge—which is calculated using glacier<!–[if supportFields]> XE “glacier” <![endif]–><!–[if supportFields]><![endif]–> velocities and ice thickness data. The gravity method uses data from the Gravity Recovery and Climate Experiment (GRACE)<!–[if supportFields]> XE “Gravity Recovery and Climate Experiment (GRACE)” <![endif]–><!–[if supportFields]><![endif]–> to estimate the rate of change of mass as a function of time. Using both these models, the authors estimated that in 2006, the Greenland and Antarctic<!–[if supportFields]> XE “Antarctic” <![endif]–><!–[if supportFields]><![endif]–> ice sheets had a combined mass loss of 475 ± 158 Gt/year, equivalent to 1.3 ± 0.4 mm/year rise in sea-level. They also estimated in the last 18 years, the acceleration in mass loss was 21.9 ± 1 Gt/year for Greenland and 14.5 ± 2 Gt/year for Antarctica, with a combined total of 36.3 ± 2 Gt/year acceleration in mass loss. Since this acceleration is 3 times larger than for mountain glaciers<!–[if supportFields]> XE “glaciers” <![endif]–><!–[if supportFields]><![endif]–> and ice caps, the authors concluded that the mass loss from ice sheets will be the biggest contributor to sea-level in the forthcoming decade. Thus, the IPPC’s projections for the contribution of ice sheets to sea-level rise<!–[if supportFields]> XE “sea-level rise (SLR)” <![endif]–><!–[if supportFields]><![endif]–> may be too conservative.

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