Natural variability of the Earth's environments: the last two climatic extremes (18000 +/- 2000 and 8000 +/- 1000 yrs BP)

The Earth's climate is tending, at a geological scale, towards a new glacia l, through an alternation of cooler/warmer episodes. However, man-induced a tmospheric pollution is increasing the natural greenhouse effect which, acc ording to models, should result in a global warming of ca. 1 degrees C to 4 degrees C within a few decades. It is therefore a priority to outline the natural variability of continental environments corresponding to a few degr ees difference relative to nowadays, in order to define the continental are as at risk and identify the strictly human-induced environmental changes li able to occur in the near future. Thus, maps of the world environments duri ng the last climatic extremes (the Last Glacial Maximum, the Holocene Optim um) corresponding respectively to -4.5 degrees C and +2 degrees C relative to present global values: based upon geological multidisciplinary data, wer e prepared by twelve international level quaternarists at a 1:25 000 000 sc ale. The major differences between the two scenarios are briefly commented. ((C) Academie des sciences / Elsevier; Paris).