ABSTRACT: Farmers today are learning how to use their properties more effectively -- more profits, less environmental degradation -- by sophisticated use of a very simple climate forecast, based on what is known as the Southern Oscillation Index (SOI); it is the difference in Sea Level Pressure between Darwin and Tahiti. After briefly discussing how farmers use this tool, we will describe our present understanding of why the SOI is an effective forecasting device.
Since this talk focuses on physics, we will go back to Newton's First Law of Motion, which states that "bodies move in a straight line at uniform speed, unless acted upon by an external force". We know from several of his examples that Newton actually meant, "bodies move in a straight line, relative to the fixed stars" -- and this even applies to deep water or magma, that cannot "see" where the fixed stars are. This statement -- which is as weird as anything Einstein came up with -- works; but it was not till Foucault played with pendulums in 1851 that physicists appreciated its power. Dynamical meteorology and oceanography started shortly afterwards.
The Southern Oscillation is basically an instability of the ocean-atmosphere climate system. The atmosphere and the ocean are both thin spherical shells of fluid that are rapidly rotating, relative to the fixed stars. Each fluid obeys Newton's Laws, and is directly or indirectly forced by solar radiation; each affects the other in ways that will be described, to give us our climate variations. If time permits, we will (very sketchily) outline the present state of play in dynamical research on climate variability.

SPEAKER PROFILE: Stuart Godfrey got a BSc with Honours in Physics at the University of Tasmania in 1961, before obtaining a PhD in High Energy Physics at Yale University in 1967. He then switched drastically, to oceanography. Apart from a year at Harvard learning what an ocean was, he has spent 30 years with CSIRO Marine Research. In 1999 Dr Godfrey received the Sverdrup Medal, awarded by the American Meteorological Society every two years to someone who has advanced the understanding of physical oceanography. Much of his time has been spent researching how the ocean affects the atmosphere, and vice versa. This coupling gives us our slow variations in climate. Much of the physics of this phenomenon dates back to Isaac Newton, but Dr. Godfrey has found it much more interesting and surprising than high energy physics.