http://downloads.climatescience.gov/sap/sap3-4/sap3-4-final-report-ch2.pdf Since the mid-19th century, small glaciers (sometimes called glaciers and ice caps; see Box 2.1 for definitions) have been losing mass at an average rate equivalent to 0.3 to 0.4 millimeters per year of sea level rise. The best estimate of the current (2007) mass balance of small glaciers is about 400 gigatons per year (Gt a1), or nearly 1.1 millimeters sea level equivalent per year. The mass balance loss of the Greenland Ice Sheet during the period with good observations increased from 100 Gt a1 in the mid-1990s to more than 200 Gt a1 for the most recent observations in 2006. Much of the loss is by increased summer melting as temperatures rise, but an increasing proportion is by enhanced ice discharge down accelerating glaciers. The mass balance for Antarctica is a net loss of about 80 Gt a1 in the mid-1990s, increasing to almost 130 Gt a1 in the mid-2000s. There is little surface melting in Antarctica, and the substantial ice losses from West Antarctica and the Antarctic Peninsula are very likely caused by increasing ice discharge as glacier velocities increase. During the last interglacial period (~120 thousand years ago) with similar carbon dioxide levels to preindustrial values and arctic summer temperatures up to 4 °C warmer than today, sea level was 46 meters above present. The temperature increase during the Eamian was the result of orbital changes of the sun. During the last two deglaciations, sea level rise averaged 1020 millimeters per year with large meltwater fluxes exceeding sea level rise of 50 millimeters per year lasting several centuries. The potentially sensitive regions for rapid changes in ice volume are those with ice masses grounded below sea level such as the West Antarctic Ice Sheet, with 5 to 6 meters sea level equivalent, or large glaciers in Greenland like the Jakobshavn Isbræ, also known as Jakobshavn Glacier and Sermeq Kujalleq (in Greenlandic), with an over-deepened channel (channel below sea level, see Figure 2.10) reaching far inland; total breakup of Jakobshavn Isbræ ice tongue in Greenland, as well as other tidewater glaciers and ice cap outlets, was preceded by its very rapid thinning.