Time Magazine: While the geologic record shows the earth has experienced rapid sea-level rise in the past, during the sharp warm-ups that follow the end of ice ages, those big melts have occurred when the world had much less ice than it does now. Scientists are unsure of how quickly rising temperatures from global warming could destabilize and melt our existing sheets — the working assumption has been that such major melting and subsequent sea-level rise would take centuries, if not longer, even in a …