Smith Lecture: The Atlantic Meridional Overturning Circulation (AMOC) and the Garden of Eden
Starting from a relatively warm and verdant state, the Earth's climate
began to deteriorate about 5 million years ago. Deserts and savannahs
replaced forests. Ice sheets developed on the northern continents.
About one million years ago, the northern ice sheets began growing and
shrinking rather wildly along with subtle changes in the Earth's orbit.
There is no obvious reason for these changes: the Earth's continents and
ocean basins were in their modern configurations; atmospheric CO2 was
apparently not much different 5 million years ago than it was during the
1950s; the Earth's orbital variations have not changed. The only
difference that one can point to is a land barrier that filled in what
had been a seaway where Panama and Costa Rica are today. In my lecture I
will describe how the little land barrier managed to bring about so much
cooling and drying and so much sensitivity to the orbital variations.
The villain is not the land barrier itself but the oceanic overturning
circulation (the AMOC) that it gave rise to.