Our legacy
There's volcanoes under the ice sheets.
http://wattsupwiththat.com/2008/01/22/surprise-theres-an-active-volcano-under-antarctic-ice/
From the guardian article http://www.theguardian.com/environment/2014/may/12/western-antarctic-ice-sheet-collapse-has-already-begun-scientists-warn
Both papers said the contact between the glaciers and the relatively warmer water at the ocean depths was the main driver of the slow-motion collapse.
Hmm, lighter warm water below heavier cold water.
Location of ice sheet
Location of a volcano
Here's more on Antarctic volcanos: Active Volcano Found Under Antarctic Ice: Eruption Could Raise Sea Levels
http://news.nationalgeographic.com/news/2013/13/131118-antarctica-volcano-earthquakes-erupt-sea-level-rise-science/
Huge Underwater Volcanoes Discovered Near Antarctica
http://www.livescience.com/15006-underwater-volcanoes-discovered-antarctica.html
We humans are no match for these volcanoes. If they become aggressive it won't take a 1000 years to melt the ice sheets.