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Résumé :
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Ecologists who have attempted in recent years to look into the crystal ball to find out what is likely to be the biosphere-to-come, will surely, sooner or later, have reached the conclusion that the future depends almost entirely on how man handles the biosphere within the coming decades. Such forecasting also involves a series of problems, such as the following: (a) How can we circumscribe our vision to make it operational? Should a specific date be set, for instance the year 2000? Or should there be a continuous or periodic appraisal over a definite period of time, as obviously we cannot foresee indefinitely into the future? (b) How far and how reliably can present trends be projected into the future? In this connection an evaluation should be made of the extent to which current trends will generate reactions by mankind, and there- by deflect some of the curves which we have drawn on the basis of past experiences. Some of these problems were admirably illustrated in a recent paper by Peccei (1971), who included part of the accompanying diagram (Fig. 1). This diagram, resulting from the use of computer simulation models, is one example of what has been obtained by the Massachusetts Institute of Technology team working under the direc- tion of Professor Jay W. Forrester and aiming at studying the dynamic behaviour of interacting systems and how they would react to certain policy changes (C. L. Wilson, 1971).
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