Photo by Liz
As everyone along the northeastern US coast knows, sea level ain't what it used to be. It's getting higher and higher and made it a lot easier for storm surges to flood low-lying cities. This is not just something figured out in the last few days. Sea level has been getting higher at an accelerating rate that has totally exceeded what climate scientists had predicted in the last official IPCC report.
So what's going on? Geologist Bill Hay of the University of Colorado thinks there are a bunch of vicious cycles at work that are not included in the climate models. The 2007 IPCC report projected 0.2 to 0.5 meters of sea level rise by the year 2100. But we are already at the high end of that trend, or ahead of it, Hay told me in a recent interview. What we are seeing now is the possibility of a sea level rise of one meter or more by the end of the century.
Yesterday, Hay talked about three glaringly missing, vicious cycles at the meeting of the Geological Society of America in Charlotte, N.C.: the Greenland ice cap, Arctic sea ice, and groundwater mining.
The Greenland ice is handled in the IPCC models like a big block of ice frozen to the bedrock. But that's all wrong. Research over the last ten years in Greenland and Antarctic shows that there is water down at the bottom of glaciers that allow them to flow. In the case of Greenland, the only thing keeping the glaciers from debouching into the sea is the grounded ice at the ocean end of the glaciers that is stuck and serves as corks.
The Arctic sea ice is a trickier matter. Melting sea ice doe not add water to the oceans or raise sea level, since the ice is already in the oceans. What it does do, however, is add cold fresh water to the Arctic Ocean. That water tends to flow out of the Arctic and is replaced with saltier and warmer waters from the south – thereby intensifying sea ice melt as well as warming throughout the Arctic. Hay calls it a heat pump.
Finally there's all that water mining, which is just another term for extracting water from the ground faster than it can be replenished by infiltrating surface waters. Droughts spur a lot of water mining and most of the U.S. is now experiencing groundwater deficits. How does this contribute to sea level rise? It does so by moving the groundwater to the surface, where it eventually ends up in the air and oceans – increasing the overall surface water volume.
What's really frightening, however, is that all these feedbacks push towards a warmer planet and there are no feedbacks pushing the other way. It's almost, Hay said, as if the Earth has certain stable climate settings, and it rushes between them. What we are seeing now is the beginning of the rush. So keep your hip waders handy.