Lectures week 4.

Tuesday:

Results of Exam 1 are posted here. The average grade was 63, with a range between 45 and 83. This is interpreted as 45-62 B, 63-83 A.

Thursday:

Solar radiation heats the surface of the earth mostly at the equator, and an equal amount of energy is lost by radiation to outer space at the poles. The ocean and atmosphere circulate and interact in complex ways to distribute this heat uniformly...with results that vary from time to time. Past climatic regimes have been very different from the present. During the Cretaceous period 100 million years ago, when the Atlantic was half formed, the temperature at the north and south poles was 9 degrees C, compared to -20 and -40 C at present. The present climate is called glacial because we have large ice masses at the poles of the planet at present. However, we can see from history that climate can switch between vastly different metastable states...that is, between tropical and glacial. In the past, astronomical events probably triggered the changes. In the future, political decisions may play a role.