What Determines Sea Level and Why is it Rising?

Bob Jacobel
Physics Department, St. Olaf College

It is perhaps widely known that sea level is rising, but how fast, why exactly and more fundamentally, what actually determines sea level?  The IPCC Fourth Assessment Report released last year projects a 30 cm rise in global average sea level over the next century, but points out “large uncertainties due to a lack of our ability to model the basic processes contributing to ice melt in dynamic areas of Antarctica and Greenland.”  What are these processes and why is obtaining an estimate of future rise such a difficult problem? 

This talk will describe the physics that determines the earth’s shape [image] and develop a definition of sea level and describe how it is measured.  It will consider the processes contributing to sea level rise and some of the (surprising) ways of measuring them remotely from space and will conclude with a discussion of why predicting future sea level still has such large uncertainty.

Earth’s geoid, the equipotential surface that most closely matches sea level.