Global environmental change occupies a central niche in the pantheon of modern sciences. There is an urgent need to know and understand the way in which global biogeochemical cycles have changed over different time scales in the past and are likely to do so in the future. Equally important, it is necessary to determine the extent to which natural variability and that induce by anthropogenic activities are bringing about change. A number of international co-operative scientific programmes ad dress these issues. Chief among them are the International Geosphere-Biosphere Programme (IGBP), the...