GLOBAL CLIMATIC CHANGES SINCE THE LAST GLACIAL MAXIMUM - EVIDENCE FROM PALEOLIMNOLOGY AND PALEOCLIMATE MODELING

Recognition that Earth/Sun orbital changes are the basic cause for Qua ternary climatic variations provides a context for explaining global e nvironmental changes, many of which are preserved in the stratigraphic and geomorphic record of lakes. Paleoclimatic numerical models sugges t the mechanisms. In subtropical latitudes such as North Africa the en hanced summer insolation culminating about 10 000 years ago resulted i n the increased monsoonal rains that explain the widespread expansion of lakes in now-desert basins. But in the American Southwest lake expa nsion dates to 18 000-15 000 years ago, when storm tracks were displac ed to the south by the ice sheets - themselves a product of earlier or bital changes. The dynamics in the response of different components of the natural system to climatic change are recorded in the stratigraph y of lake sediments, not only by their pollen content as a manifestati on of the regional vegetation but also by their microfossils and chemi cal composition as reflections of lake development.