WHILE there is concern about possible future climate change, we should pay attention to what is happening today. What we believe to be "normal" climate may not be normal at all.
This is especially important in the case of precipitation and water supply. Inhabitants of some parts of the globe may have based their assessment of long-term average water supplies on their experience with weather in this century that really isn't normal at all. They should consider their weather in the perspective of previous centuries.
For example, the drought that has parched western parts of the United States for the past six years may be a normal climatic feature. Studies at the University Of Arizona's laboratory for tree-ring research in Tucson indicate that long-running droughts are a recurring feature. The relatively wet decades of 1937 through 1986 may be abnormal.
Likewise, the long-playing drought that has brought famine to Africa's Sahel region south of the Sahara Desert also might appear to be anomolous. Research by several scientists over the past decade, however, has shown that the drought is not an aberration. This research includes studies of pollen samples that reflect conditions ranging back as far as 18,000 years ago.
Referring to this growing evidence, ecologist Peter D. Moore of Kings College, London, has observed that "climatic fluctuations in the Sahel, which produce such distressing social consequences, have evidently been proceeding for a very long time."
The western United States and African Sahel are two examples of regions where people are feeling stress because their expectations don't conform to climatic reality. Climate hasn't changed. What has changed is the human population density. These places and many other areas of the world have more people than the normal water resources can sustain.
Sandra Postel of the Worldwatch Institute in Washington warns that this problem is especially acute in Africa and the Middle East. …