The Climate System and The Second Law of Thermodynamics

This course will read and discuss a recent review of the climate system with a focus on modeling the Earth's atmosphere as a heat engine, and quantifying entropy balance and entropy production in the moist atmosphere. The Earth receives a small amount of entropy from the sun, and radiates an enormous amount of entropy out to space. In a steady state climate system, this indicates that the atmosphere and ocean irreversibly produce substantial entropy to remain in balance. How this entropy is produced impacts the mechanical efficiency of the atmosphere. We will construct a detailed entropy budget for a dry and then moist atmosphere, emphasizing the substantial role that moisture plays in an atmospheric heat engine's ability to perform work on itself. We will consider several scales, from tropical cyclones to the full planetary circulation, and then consider how these may change under climate change and on other planets. We will also briefly discuss variational principles that minimize or maximize various quantities in order to understand the statistically steady-state climate system. The weekly class will be a discussion and work-through of the review paper.