Trends in ice sheet mass balance

The Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE) is a community effort supported by ESA and NASA that aims to provide a consensus estimate of ice sheet mass balance. In its first phase, IMBIE showed that estimates of ice sheet mass balance derived from satellite gravimetry, altimetry and the mass budget method could be reconciled within their respective uncertainties. In its second phase, IMBIE showed that rates of ice loss from Antarctica and Greenland have increased by a factor 6 during the satellite era and are tracking the high-end (worst-case) projections reported in the IPCC’s fifth assessment report (AR5). The project now involves 96 individual participants based in 50 institutes from 13 nations and includes 26 satellite estimates of ice sheet mass balance, 11 models of glacial isostatic adjustment, and 10 models of surface mass balance. IMBIE has now begun its third phase, and the objectives are to (i) include measurements from new satellite missions, (ii) to report annual assessments, (iii) to partition changes in mass due to ice dynamics and surface mass balance, (iv) to produce regional assessments in areas of imbalance, and to (v) explore remaining biases between the various geodetic techniques involved. Participation is open to the full community, and the quality and consistency of submissions is regulated through a series of data standards and documentation requirements. This paper will introduce the objectives of IMBIE-3 and present the latest assessment of ice sheet mass balance. which has been updated for the IPCC's sixth assessment report.