But that study's scenario for abrupt change hinged in part on fears that the Atlantic's Gulf Stream current might slow, chilling northern Europe and eastern North America and curtailing food harvests. Now, however, the Intergovernmental Panel on Climate Change says it's ''very unlikely'' the current will slow abruptly.
Unpredictability was dispelled elsewhere in the panel's reports this year. It found, for example, that warmer and drier conditions are already shortening the growing season in Africa's Sahel, a conflict-ridden region long burdened by food and water shortages.
The Intergovernmental Panel on Climate Change and the German scientists cited other potential ''hotspots,'' including:
— Egypt's vital, low-lying Nile Delta, where the livelihoods of millions may be at risk from rising sea levels and salinization of agricultural areas.
— The Asian subcontinent, where the retreat of Himalayan glaciers will dry up downstream water supplies, and rising seas and stronger cyclones will threaten tens of millions on the Bay of Bengal coast.
— The poor nations of Central America, where more intense hurricanes could severely damage economies, destabilize political systems and send streams of uprooted people toward the U.S. border.
At the same time, the German scientists said, the climate challenge is an opportunity to unite the international community. In that spirit, Britain last April organized the first U.N. Security Council meeting to consider climate change as a threat to international peace.
Global efforts have faltered, however, in trying to cut back emissions of carbon dioxide and other global-warming gases — in part because the Bush administration opposes such internationally mandated reductions. That in itself may help sharpen world tensions, the German report said.
If, amid recriminations and finger-pointing, governments fail to unite on global warming, ''climate change will draw ever-deeper lines of division and conflict in international relations,'' it said.
Leaders are growing nervous. At the U.S. Army War College last March, military and scientific specialists quietly convened in a colloquium on ''Global Climate Change: National Security Implications.'' Among the topics discussed: the possible need for a new National Security Act to ''oblige intergovernmental cooperation'' on climate by future U.S. administrations.