The state of the environment in the latter part of the next century will be determined largely by one factor: human population. If the species doubles its numbers by 2050, to nearly 11 billion, humanity may complete the devastation that accelerated so steeply in this century. Such unabated expansion in our numbers would continue to soak up the world's capital and prevent the poorer nations from making the necessary investments in technological development that might deter continued population growth.
If the worst occurs, countless millions will become environmental refugees, swamping the nations that tried to conserve their soil, water and forests. The great-grandchildren of today's young people would have to share the planet with only a ragged cohort of adaptable species dominated by rats, cockroaches, weeds, microbes. The world in which they survived would consist largely of deserts, patches of tropical forests, eroded mountains, dead coral reefs and barren oceans, all buffeted by extremes of weather.
The best hope for both humanity and other life-forms would be to cut human propagation in half, so the world's numbers do not exceed 8 billion by mid- century. (The only event in which the earth would achieve zero population growth or even shrinkage would be some environmental or social catastrophe.) The huge run-up in human numbers has foreclosed most options and shortened the amount of time available to come to grips with rising threats to the environment, contends systems analyst Donella Meadows, co-author of Beyond the Limits, which updates the controversial 1972 blockbuster The Limits to Growth. In the past, says Meadows, there were always new frontiers for exploding populations, as well as empty lands to accept wastes. No longer: most suitable areas have been colonized, most easy-to-find resources are already being exploited, and most dumping grounds have filled up. "If humans manage brilliantly starting very soon," Meadows believes, "it is possible the world might look better than it does now."
Still, for centuries humanity has confounded doomsayers by finding new supplies of food and energy. In the early 1970s some environmentalists interpreted temporary rises in food and oil prices to mean mankind was again pushing the limits of earthly resources, yet surpluses returned in later years. Julian Simon, among other economists, argued that this revealed a basic problem with the limits-to-growth argument. Price rises caused by scarcities, he argued, will always stimulate human ingenuity to improve efficiency and find new resources.
In the intervening years, however, there has been evidence that the market often fails to react as quickly as problems demand. The world took 15 years to respond to signs of ozone depletion in the upper atmosphere, but because ozone-destroying chemicals take 15 years to migrate to that stratum, the real delay amounts to 30 years. Moreover, these chemicals can remain in the atmosphere as long as 100 years. In addition, market forces often work perversely to hasten the demise of species and resources. The increasing appetite for bluefin tuna among sushi lovers and health-conscious diners has vastly increased the market price of the fish. But instead of dampening demand, the principal effect has been to encourage further fishing, to the point that the total number of the magnificent pelagic fish in the Atlantic has dropped 94% since 1970.