SOMETIME within the next decade, the world will pass a major population mark. (Not the one that puts us over 6 billion people; that will happen in less than five years.) This one will see the urban-rural balance shift to a majority in cities and towns for the first time. And the effect of this fact - and the demographic trend that is preceding it - will have profound environmental consequences.
This was the message of a World Bank gathering in Washington last week that brought together some 900 urban leaders from around the world. During the week those leaders were talking, the globe's urban population grew by 1 million. In the developing world, where more than 90 percent of the world's population increase is occurring, the annual growth rate in urban areas is 3.8 percent.
Less than 4 percent growth doesn't sound like much, but it means a doubling in less than 19 years. It means that during the last decade of the 20th century, the number of cities with populations greater than 1 million will grow from 288 to 391. It means there will be 26 ``megacities'' (those with populations of more than 10 million), 21 of them in the developing world. And it means that just one city - Sao Paulo, Brazil - is likely to have as many people as all the world's cities did at the beginning of the Industrial Revolution: 25 million.
There are several reasons to be concerned about this, the first of which is the conditions under which many people in urban areas live. For them, the environment means basics like air and water. The figures are grim: More than 1 billion urban dwellers in developing countries (65 percent of the total) breathe unhealthy air, according to World Bank figures. At least 170 million don't have easy access to drinkable water. Some 350 million lack adequate sanitation. Only 40 percent are connected to sewers, 90 percent of which spew out untreated waste.
The economic costs of urban pollution are climbing. Health-care costs associated with dirty air amount to $200 million a year in Jakarta, Indonesia, and $1.5 billion in Mexico City. Air and water pollution cost Manila $120 million in lost productivity every year.
The human costs, of course, are even more troubling. Increasingly, the nearly 40,000 children who die each day from environmental degradation (mainly dirty water) live in urban areas. This is why the World Bank is shifting its environmental programs from a ``green agenda'' (natural resources and the rural environment) to what it calls a ``brown agenda,'' the environmental problems facing cities.
``Protecting the rain forest - and protecting biodiversity - is important, because it will preserve natural resources for the next generation,'' said World Bank President Lewis Preston, ``but cleaning up cities will help hundreds of millions of people right now.''
There is also recognition that both goals work together. Most cities, for example, are in coastal areas. To the extent that sewage is controlled and treated, marine habitat will be protected. This is very important, given the decline in fisheries all around the world. ``Green agenda'' loans and grants from the World Bank and other donors can improve agricultural productivity, which should help reduce migration to urban areas.
This in turn will help prevent the urban sprawl that eats up valuable farmland.
``There is an interdependency,'' bank senior adviser Michael Cohen told the Reuters news agency. ``You save cities in part to save forests, because if you aren't more energy-efficient, for example, people cut down more trees.''
Above all, the World Bank report points up the need to rein in population growth rates. Without that, cleaning up the urban environment - and the environment generally - will be much tougher.