Book Review; March 1993; Scientific American Magazine; by Robert M. May; 4 Page(s)
People have always felt that the times in which they lived were special: the best of times, the worst of times, and sometimes both together. The feeling tends to be particularly strong at points of calendric resonance, such as the end of centuries, much less the end of millennia. But our own times are special, by many objective measures, in that the scale and scope of human activities have, for the first time, grown to rival the natural processes that built the biosphere and that maintain it as a place where life can flourish.
Many facts testify to this statement. It is estimated that somewhere between 20 and 40 percent of the earth's primary productivity, from plant photosynthesis on land and in the sea, is now appropriated for human use. The global amounts of biologically available nitrogen and phosphorus associated with fertilizers and other chemicals used in agriculture rival the amounts mobilized by natural processes. Macroscopic holes in the ozone layer have been created by chlorofluorocarbons. Carbon dioxide from the burning of fossil fuels and tropical forests, along with other greenhouse gases, is changing the composition of the earth's atmosphere in ways that, if continued, seem likely to cause global environmental changes on as large a scale as those that took place during the ice ages, and faster; the many significant nonlinearities in the landocean-atmosphere system make precise forecasts impossible at this point. And it seems probable that today's species of plants and animals stand on the curling tip of a wave of extinction more rapid and extensive than any in the fossil record.