Mass balance of glaciers and ice caps: Consensus estimates for 1961-2004

Working with comprehensive collections of directly-measured data on the annual mass balance of glaciers other than the two ice sheets, we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960. Mass balance was slightly below zero around 1970 and has been growing more negative since then. Excluding peripheral ice bodies in Greenland and Antarctica, global average specific balance for 1961-1990 was -219 +/- 112 kg m(-2) a(-1), representing 0.33 +/- 0.17 mm SLE (sea-level equivalent) a(-1). For 2001-2004, the figures are -510 +/- 101 kg m(-2) a(-1) and 0.77 +/- 0.15 mm SLE a(-1). Including the smaller Greenland and Antarctic glaciers, global total balance becomes 0.38 +/- 0.19 mm SLE a(-1) for 1961-1990 and 0.98 +/- 0.19 mm SLE a(-1) for 2001-2004. For 1991-2004 the glacier contribution, 0.77 +/- 0.26 mm SLE a(-1), is 20-30% of a recent estimate of 3.2 +/- 0.4 mm a(-1) of total sea-level rise for 1993-2005. While our error estimates are not rigorous, we believe them to be liberal as far as they go, but we also discuss several unquantified biases of which any may prove to be significant.