• The land-based ice sheets of Greenland and Antarctica hold enough water to raise global sea level by more than 200 feet
• Three ice sheets (Greenland, Western Antarctica, Eastern Antarctica) hold 99% of the ice that would raise sea levels if global warming caused it to melt or go afloat (the remaining 1 % is locked up in mountain glaciers)
• Water under ice, no matter how it gets there, can lubricate the contact between bedrock and the bottom of an ice sheet. In Greenland for example, the warming Arctic climate has led to melt water on the surface that gushes into crevasses and drains to the base of the ice sheet. The drainage is closely linked to the acceleration of movement of ice towards the ocean.

Fore more information on ice sheets check out:

• Charles R. Bentley, Robert H. Thomas and Isabella Velicogna. Ice Sheets.