According to Joe Romm, blogging a recent Nature study, that's what's possible--or at least, it appears to have happened in the planetary past, some 121,000 years ago. The numbers, Romm notes, translate into an 8 foot rise over 50 years. How could such a quick increase in sea level happen? Well, the collapse of a massive ice sheet might do it. And when might that happen? Nobody knows. As this discussion underscores, by far the greatest threat from global warming is catastrophic sea level rise. Yet given our current understanding of ice sheet dynamics, it's also a very poorly understood risk. Still, if there were ever a time to err on the side of caution, this is it. Romm writes:
If sea levels were even 3 feet higher in 2100 (let alone 5 or higher) and rising 1 to 2 inches a year at that point, it would be the single greatest preventable catastrophe in human history.
All those who worry about the risks to the "economy" if we take climate action now, here's a thought for you: What happens to the economy if coastal cities and major financial centers have to retreat from rising seas?