The new book involves paleoanthropology, paleoclimate, and considerations from neurobiology and evolutionary biology:

Human Evolution and Abrupt Climate Change

will be out in Spring 2002 from the University of Chicago Press.  It is already posted full-text on the web and also as a free e-book in Palm download format, for reading on the commute. 

It includes the climate history and flip mechanisms that I described in The Atlantic Monthly, together with dozens of photos, maps, and graphs.  See also