The North American Ice Sheet (Proper name:the Laurentide Ice Sheet) melted about 20,000 years ago and was the most recent cause of world wide sea level rise, a rise that increase how much sea water comes in contact with the West Antarctic Ice Sheet (Which is grounded BELOW sea level).
Saying that, The West Antarctic Ice Sheet is theory should have collapsed centuries ago, but it has not. Thus the ice sheet is hanging on, but can give at any spring (i.e March 1 to April 15, the Ice Shelves that surround the West Antarctic Ice Sheet, retreat from September to about March 23 every year. by the first day of Spring in the Northern Hemisphere (First day of Autumn in the Southern Hemisphere) the Ice Shelves are at their smallest and thus provide the least protection to the Ice Sheets. Thus the time for the break up of the West Antarctic Ice Sheet is March to mid April (and most probably March 15 to April 1st).
Definitions:
ICE SHELVES: Ice that is FLOATING on water. The water the ice in an Ice Sheet would replace if melted, equals to the water the ice is displacing as it floats on the water. Thus the melting of an Ice Shelf will have little to no affect on world wide sea levels. Through a lost of Ice Shelves make the Ice Sheets more exposed to warm temperatures thus may be the key to why the West Antarctic Ice Sheet has NOT collapsed over the last 20,000 years.
ICE SHEET: Ice that is GROUNDED, i.e. laying on ground, including the sea floor. An Ice Sheet CAN exist BELOW Sea level (as it does in the West Antarctic Ice Sheet). An Ice Sheet does displace some of the water it has pushed out of its way, but it can contain more water as ice then it is displacing. In the case of the West Antarctic Ice Sheet it is Grounded on the sea floor, its ice content exceeds what water it is displacing. If the West Antarctic Ice Sheet breaks up and FLOATS (and thus becoming an Ice Shelve or an Iceberg) this would displace enough water to raise world wide sea levels 15-20 feet. Thus the West Antarctic Ice Sheet is called the "Godzilla" of global warming.
Thus, the West Antarctic Ice Sheet can collapse any year and your guess is as good as mine. On the other hand, it will be close to the First day on the Northern Spring (about March 23) which is also the Southern first day of Autumn. Outside guess March 1 to April 15, mostly likely March 15 to April 1st. Thus we can estimate the time of year of the Collapse, but not the year.
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