Melting ice and sea level

Washington Post:

Few consequences of global warming pose as severe a threat to human society as sea-level rise. But scientists have yet to figure out how to predict it.

And not knowing what to expect, policymakers and others are hamstrung in considering how to try to prevent it or prepare for it.

To calculate sea-level rise, the key thing researchers need to understand is the behavior of the major ice sheets that cover Greenland and Antarctica. The disintegration of one would dramatically raise the ocean. But while computer models now yield an increasingly sophisticated understanding of how a warming atmosphere would behave, such models have yet to fully encapsulate the complex processes that regulate ice sheet behavior.

"The question is: Can we predict sea level? And the answer is no," said David Holland, who directs New York University's Center for Atmosphere Ocean Science. Holland, an oceanographer, added that this may mean researchers will just have to watch the oceans to see what happens: "We may observe the change much more than we ever predict it."

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The concern must be for ice melting over a land mass since ice that is already floating is of little consequence. To prove that fill a glass with ice and add water to it and let the ice melt. The volume in the glass will actually shrink some. If you put the same container in a freezer you would find measurable swelling. What this tells us is that AlGore's polar bear shots are pretty meaningless.

I think that the other thing that should work into the calculation is the effect of water vapor evaporating into the air as the temperature rises. You see it all the time in inland water masses like lakes and ponds. My one acre pond can lower by a foot or more in a matter of weeks just from evaporation when there is no rain runoff to spill into it. But runoff varies depending on the dryness of the soil which can absorb a significant amount of water before it allows the excess to escape.