Greenland Ice Sheet Mass Balance (1992–2020) From Calibrated Radar Altimetry.

We present the first 1992–2020 record of Greenland Ice Sheet (GrIS) mass balance derived from multisatellite Ku‐band altimetry. We employ an empirical approach as an alternative detailed to radar‐propagation modeling, and instead convert elevation changes observed by radar altimetry into mass changes using spatiotemporal calibration fields. This calibration field is derived from a machine learning approach that optimizes the prediction of a previously published mass balance field as a function of ice sheet variables. Our mass balance record shows a GrIS contribution of 12.1 ± 2.3 mm sea‐level equivalent since 1992, with more than 80% of this contribution occurring after 2003. Our record also suggests that the 2017 hydrological year is the first year in the 21st century which, within uncertainties, the GrIS was in balance. Overall, the 28‐year radar‐derived mass balance record we present highlights the potential of the method to provide operational mass balance estimates derived from multisatellite Ku‐band altimetry. Plain Language Summary: Earth's land ice masses are shrinking due to climate change. The Greenland Ice Sheet (GrIS) has been a major contributor to sea‐level rise in recent years. Earth‐observing satellites have enabled us to monitor ice‐sheet changes, but common problems for these estimates of ice‐sheet mass balance are mission gaps and changing instrumentation. Since 1991, the European Space Agency has used the same instrumentation for satellite radar altimeters in orbits applicable for monitoring the GrIS. Additionally, before retiring one satellite altimeter, a replacement has been commissioned with a sufficient timespan of overlapping measurements to estimate offsets between satellites. The resulting satellite altimetry record can be processed to provide a lengthy, and consistent, record of ice‐sheet elevation and volume changes. Here, we apply machine learning to convert radar‐derived volume changes to radar‐derived mass changes. This novel mass balance record shows a contribution from the GrIS to global sea level rise of 12.1 ± 2.3 mm since 1992, with more than 80% of this contribution originating after 2003. The method we present is an alternative to modeling both radar propagation and firn compaction, and provides a path toward operational mass‐balance estimates from satellite altimetry. Key Points: Novel estimate of Greenland Ice Sheet mass balance from calibrated multisatellite Ku‐band altimetryTotal eustatic sea‐level rise contribution of 12.1 ± 2.3 mm from the ice sheet since 1992Atmospheric circulation can shift ice‐sheet mass balance by 3σ within 5 years [ABSTRACT FROM AUTHOR]