Ice shelves are the floating extensions of the glacial ice that has moved under gravity from the grounded portion of the ice sheet to the ocean. Ice shelves can be hundreds to thousands of meters thick. For a tour of Antarctic ice shelves, go to the National Snow and Ice Data Center (NSIDC) Ice Shelves and Icebergs page.
Ice shelves are strongly influenced by atmospheric and oceanic conditions, including snow fall, air temperature, solar radiation, and the flow of "warm" ocean water under the shelves. As a result, they are expected to respond rapidly to significant shifts in global climate, whether caused by natural variability (e.g., ice age cycles) or anthropogenic action (the "Greenhouse Effect"). The thickness and extent of ice shelves can be routinely monitored from space, with sensors such as radar on the European Space Agency's ERS satellites, and the Geoscience Laser Altimeter System (GLAS), which will be carried on the forthcoming ICESat mission. However, satellites only obtain data at specific points on the ice shelves every few days to every few months (the tradoff being whether you want frequent data on a coarse spatial grid, or infrequent data on a fine grid). Regardless of the choice of orbit parameters, most of the variability of ice shelf height is actually due to processes that occur with very short time scales. The two dominant high-frequency processes affecting ice shelf height are TIDES, and the INVERSE BAROMETER EFFECT (IBE).