No Tropical Drought in the Paleocene-Eocene Thermal Maximum

There is a paper that just came out (subscription required) in the current issue of Science that is encouraging with respect to the possibility of widespread drought under global warming.  The paper concerns the Paleocene-Eocene Thermal Maximum.  This is an episode about 55 million years ago when, for reasons that aren't altogether clear, there was a large release of carbon into the atmosphere.  The leading theory is that it might have been caused by volcanic intrusion into carbon rich sediments in the North Atlantic.  At any rate, over the course of about 20,000 years, global temperatures rose about 6^oC (11^oF) from a base already warmer than today.  There was a global extinction event, with large amounts of ocean flora disappearing.  There was also a large number of new species created, including many new types of mammals.

The episode is of obvious interest as a prototype for what is presently happening with human-caused CO₂ emissions, though it clearly isn't a perfect analogy.  It happened a long time ago in a world that was quite different in important respects, and the rate of emissions was significantly slower than modern anthropogenic emissions.

In any case, the new paper concerns what happened in the South American tropical forests during the PETM, and comes from analyzing pollen from sediments at three sites in Columbia and Venezuela.  The good news is twofold: