If the West Antartic Ice Sheet (WAIS) would Collaspe tomorrow, worldwide sea level would raise about 7 Meters or 20 feet within weeks.
World wide map with various sea level increases:
http://geology.com/sea-level-rise/
The area this subway will be on would still be way above sea level. If the Greenland Ice Sheet would melt a similar raise in sea levels would occur, and it still would be above sea level. The area only comes under the threat of being under water if the East Antarctic Ice Sheet (EAIS) melts. The WAIS and the Greenland Ice Sheet each contain about 10% of world wide fresh water, the WAIS contains 60% (Rivers, lakes, mountain glaciers etc holds the remaining 20%). The lost of the WAIS or the Greenland Ice sheets will raise world wide water levels about 7 meters each, the EAIS would raise world wide sea levels 60 Plus meters.
Right now the WAIS and the Greenland ice sheets are losing ice and water. The EAIS is either holding its own or gaining a small amount of additional ice (Consistent with the theory on Global warming, the EAIS is the coldest ice sheet and its ice sheet is within the Antarctic circle AND above sea level, the Greenland Ice Sheet is also above sea level but straddles the Arctic Circle, while the WAIS is grounded BELOW sea level, making both of them unstable). Thus the concern is the WAIS and the Greenland Ice Sheets not the EAIS (through as the world warms up even the EAIS will melt, but that is not expected for another 100 years or so, unlike the WAIS which can go in any spring, i.e. March through till about April 1st, the Antarctic ice cap minimum, and the Greenland ice sheet, which is expected to melt over the next few decades).
Thus looks like this subway is safe for the foreseeable future.
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