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Shoring up cities such as New York, Los Angeles, Paris, London and Rio de Janeiro would require equally monumental measures. In the U.S. the Environmental Protection Agency estimates that the cost of protecting developed coastal areas could reach $111 billion. Southern Louisiana, which is losing land to the Gulf of Mexico at the alarming rate of one acre every 16 minutes, has already drawn up an ambitious mix of programs. In the biggest project, a $24 million pumping station would divert millions of gallons of silt-rich Mississippi River water onto the coastline to help stop saltwater intrusion and to supply sediment that will build up the eroding land. At least one parish is considering plans for a backstop dike to give residents time to escape should the sea finally reach their doors.
Poorer countries have fewer options. Wracked by periodic floods, Bangladesh cannot simply evacuate the "chars" -- bars of sand and silt in the Ganges Delta -- where millions of people have set up camp. But the government has drawn up plans for a network of raised helipads and local flood shelters to facilitate the distribution of emergency aid if, as seems inevitable, disaster strikes again. Meanwhile, the country can only appeal to its Himalayan neighbors to do something about the root cause of the flooding: the deforestation of watersheds in India and Nepal that has turned seasonal monsoons into "unnatural disasters."
The problems of agriculture are likely to be critical in the next century, as growing populations, deteriorating soil conditions and changing climates put even more pressure on a badly strained food-supply system. In parts of sub-Saharan Africa, that system has broken down periodically over the past 20 years, resulting in the familiar TV images of children with swollen bellies and relief camps filled with hungry people.
What is not so well known is that hundreds of grass-roots organizations in Africa are taking action to cope with environmental change. Somalia has launched a vigorous antidesertification drive that includes a ban on cutting firewood. In Burkina Faso villagers have responded to steadily dwindling rainfall by building handmade dams and adapting primitive water-gathering techniques. Even so simple a trick as putting stones along the contour lines of a field to catch rainwater can make the difference between an adequate harvest and no harvest at all.
Necessity has spawned invention in marginal farmlands around the world. The Chinese, threatened by a desert that is spreading at the rate of 600 sq. mi. a year, are planting a "green Great Wall" of grasses, shrubs and trees 4,350 miles across their northern region. In Peru archaeologists have revived a pre- Columbian agricultural system that involves dividing fields into patterns of alternating canals and ridges. The canals ensure a steady supply of water, and the nitrogen-rich sediment that gathers on their floors provides fertilizer for the crops.