Business as usual + sea level rise = losses of up to 9% of global GDP

Although New York City would have flooded due to Sandy no matter what, the extent of the flooding was exacerbated by the sea level rise of the last century.

Climate.gov

Things like extreme weather and droughts are the high-profile impacts of climate change—they are easy to see and understand. Sea level rise is much more subtle and slow-moving, but it's inexorable. Even if we stabilize our climate at a new, higher average temperature, the seas will continue to rise for centuries as the added warmth slowly melts ice and causes the water in the oceans to expand in volume.

However, since so much of human infrastructure is built right on the coasts, the rising ocean levels have the potential to cause more disruption than any other factor. Recently, some researchers attempted to quantify just how damaging sea level rise will be. At its high end, the costs are staggering: a touch over nine percent of the global GDP by the end of this century. However, that number assumes we'll keep building right on the coasts—and we're not really that shortsighted, right?

Projecting the costs involved with sea level rise by the end of the century is a difficult challenge. To begin with, the height of the seas will depend on the rate of warming, which will depend on the trajectory that emissions (and thus temperatures) take. So there are both cultural uncertainties—will we get our carbon emissions under control or not?—and scientific uncertainties about the rate of warming and how that rate will be reflected in ocean levels.