Vast human migrations seem inevitable.

• Position: Climate Change

By mid century, people may be fleeing rising seas, droughts, floods, and other effects of changing climate, in migrations that vastly could exceed the scope of anything before, maintains a report by researchers at Columbia University's Center for International Earth Science Information Network, United Nations University, and CARE International.

The researchers say that the effects of climate are hard to sort from connected factors, including political and economic conflicts, extreme weather events, population growth, human destruction of ecosystems, and overuse of farmland. However, climate change eventually will play a dominant role by exacerbating all of these problems, and already is having detectable effects.

While the report does not attempt to put numbers to those potenlially uprooted, estimates from other reports it cites range from 25,000,000 to 50,000,000 by 2010. to almost 700,000,000 by 2050.

"Climate is the envelope in which all of us lead our daily lives. This report sounds warning bells," states co-author Alexander de Sherbinin, a senior staff associate for research at Columbia. "We usually categorize the poor as the ones who will suffer most--but richer societies will potentially lose as well."

The report is based on a first-'rime global survey of environmental change and migration. It is illustrated with a series of detailed maps that shows how and where significant displacements may occur. Among its findings:

* Breakdown of ecosystem-based economies--including subsistence herding, farming, and fishing--will be the dominant driver of forced migration. * Climate change will increase the frequency and intensity of natural hazards such as cyclones, floods, and droughts. Rains in parts of Mexico and Central America, for instance, are projected to drop as much as 50% by 2080. Farmers in parts of Mexico and North Africa's Sahel region may be moving already in part due to changing rains.

* Sea level rise directly threatens the existence of some 40 countries. Saltwater intrusion, flooding, and erosion could destroy agriculture in the densely populated Mekong, Nile, and Ganges deltas. A rise of six feet--well within some projections for this century-would inundate nearly half the Mekong's 7,500,000 acres of farmland. Soma Pacific island nations, including the Maldives (pop. 300,000), already are considering prospects for total relocation.

* Ongoing melting of alpine glaciers in the Himalayas will devastate the heavily irrigated...