Ice Sheet Mass Balance Inter-comparison Exercise

Ice Sheet Mass Balance Inter-comparison Exercise. The Ice Sheet Mass Balance Inter-comparison Exercise is a major international scientific collaboration established to reconcile estimates of ice sheet mass change. Coordinated by the European Space Agency and NASA, it synthesizes data from satellite missions like GRACE and CryoSat-2 with results from numerous independent research teams. Its primary goal is to produce a definitive, consensus estimate of contributions from Greenland and Antarctica to global sea level rise, providing critical data for reports by the Intergovernmental Panel on Climate Change.

Overview and Objectives

The initiative was formally launched in 2011 by the European Space Agency's Climate Change Initiative in partnership with NASA's Jet Propulsion Laboratory. The core objective was to address significant discrepancies in published estimates of ice sheet mass balance from various satellite techniques and modelling groups. By creating a standardized framework for comparison, IMBIE aimed to reduce uncertainty and build a robust, community-endorsed record. The exercise directly supports assessments by the Intergovernmental Panel on Climate Change and informs international climate policy discussions, such as those under the United Nations Framework Convention on Climate Change.

Participating Models and Methods

IMBIE synthesizes results from three primary satellite geodetic methods: altimetry from missions like CryoSat-2 and ICESat, gravimetry from the GRACE and GRACE-FO missions, and the input-output method which combines data from radar interferometry and regional climate models. Dozens of international teams, including from the University of Leeds, the University of California, Irvine, and the Alfred Wegener Institute, contribute processed data. A key innovation is the use of a common geographic information system mask and time series protocol to ensure direct comparability between the disparate methodological approaches.

Key Findings and Results

The landmark IMBIE assessment published in Nature in 2012 provided a reconciled estimate that both Greenland and Antarctica were losing mass at an accelerating rate. A subsequent 2018 study in the same journal concluded that ice loss from Antarctica had tripled since 2012, while loss from Greenland had increased fivefold since the 1990s. These consensus findings, which attributed the dominant mass loss to increased ice shelf melting and glacier dynamics, have become the benchmark figures cited in major reports like the IPCC Fifth Assessment Report and the IPCC Special Report on the Ocean and Cryosphere.

Impact on Climate Science

IMBIE has profoundly influenced the field of cryosphere science and climate change projections. Its authoritative, multi-method consensus has effectively ended debates about the sign and magnitude of ice sheet contributions to sea level rise, shifting scientific focus to processes and future projections. The datasets are foundational for calibrating and validating ice sheet models used in initiatives like the Ice Sheet Model Intercomparison Project. Furthermore, the IMBIE protocol has served as a model for other community inter-comparisons, such as those for glacier mass balance.

Future Directions and Challenges

Future phases of IMBIE aim to incorporate higher-resolution data from newer satellite missions like ICESat-2 and to extend the mass balance record further back in time. A major challenge is partitioning mass change into its component processes—surface mass balance versus ice dynamics—with greater precision. The collaboration also seeks to improve estimates of East Antarctica's mass balance, a region with higher uncertainty. Ongoing coordination with modeling groups within the World Climate Research Programme is essential for improving projections of future sea level rise for coastal cities like Miami and Shanghai.

Category:Climate change assessment and attribution Category:Scientific collaborations Category:Ice sheets