IMBIE is an international collaboration of polar scientists providing improved estimates of the ice sheet contribution to sea level rise, and generating consensus estimates of ice sheet mass balance by combining the geodetic techniques of gravimetry, altimetry and the mass budget method.  The first phase of IMBIE involved 27 science teams, delivering a community assessment of ice sheet mass imbalance to replace 40 individual estimates (Shepherd et al., 2012).

The main conclusions were that:

  1. Given common spatial and temporal domains, and geophysical corrections, there is good agreement between the three different satellite-based techniques of altimetry, gravimetry and the mass budget method for estimating ice sheet mass balance.
  2. Combining satellite data sets leads to a threefold improvement in certainty compared to that of the fourth IPCC assessment report.
  3. The polar ice sheets contributed 11 ± 4 mm to global sea levels between 1992 and 2012.
  4. Losses from the polar ice sheets have increased over time, and their contribution to sea level is up from 10% of the global trend in the early 1990s to 30% in the late 2000s.
Cumulative ice sheet contribution to sea level determined from a reconciliation of satellite altimetry, InSAR, and gravimetry.

Cumulative ice sheet contribution to sea level determined from a reconciliation of satellite altimetry, InSAR, and gravimetry.

With new satellite missions, geophysical corrections, techniques and teams producing data, demand for an updated assessment has grown. The period of overlap between independent satellite techniques has meanwhile increased from 5 to 12 years, and the full period of satellite data over which an assessment can be performed has increased from 19 to 40 years. It is also clear that multiple satellite techniques are required to confidently separate mass changes associated with snowfall and ice dynamical imbalance – information that is of critical importance for climate modelling.

Currently underway, the second phase of IMBIE will deliver annual assessments of ice sheet mass balance over a three year period, with the first scheduled for the end of 2016. It will also broaden participation among the wider scientific community.

Key reference

Shepherd, A., Ivins, E.R., Geruo, A., Barletta, V.R., Bentley, M.J., Bettadpur, S., Briggs, K.H., Bromwich, D.H., Forsberg, R., Galin, N., Horwath, M., Jacobs, S., Joughin, I., King, M.A., Lenaerts, J.T.M., Li, J., Ligtenberg, S.R.M., Luckman, A., Luthcke, S.B., McMillan, M., Meister, R., Milne, G., Mouginot, J., Muir, A., Nicolas, J.P., Paden, J., Payne, A.J., Pritchard, H., Rignot, E., Rott, H., Sørensen, L.S., Scambos, T.A., Scheuchl, B., Schrama, E.J.O., Smith, B., Sundal, A.V., Van Angelen, J.H., Van De Berg, W.J., Van Den Broeke, M.R., Vaughan, D.G., Velicogna, I., Wahr, J., Whitehouse, P.L., Wingham, D.J., Yi, D., Young, D., Zwally, H.J. (2012) A reconciled estimate of ice-sheet mass balance, Science, 338 (6111), pp. 1183-1189 doi:10.1126/science.1228102