A melting or collapse of the West Antarctic Ice Sheet (WAIS) would raise sea level by 5 or more meters and inundate a large amount of coastal area and many major cities around the world. Evidence reported by Scherer et al. (1998) strongly indicates that the WAIS disintegrated in one of the recent warm episodes in the geological past, probably about 400,000 years ago. This evidence of past ice sheet demise increases the likelihood of accelerated sea level rise beginning in the 22nd century (Kerr, 1998).
References
Kerr, R. A., 1998: Signs of past collapse beneath Antarctic ice. Science, 281, 17-18.
Scherer, R. P., A. Aldahan, S. Tulaczyk, G. Possnert, H. Engelhardt, and B. Kamb, 1998: Pleistocene collapse of the West Antarctic Ice Sheet. Science, 281, 82-85.