Darfur, a region of western Sudan, is one of the most troubled and violent areas in the world. Since 2003, it has been the site of a bitter civil war between Arab militias (possibly allied with the Sudanese government) and black rebel groups. The war has been characterized by mass murders and rapes of civilians, and it is often referred to as a genocide.
In general, the fight in Darfur is seen as an ethnic conflict. In a 2007 article in the Washington Post, however, Ban Ki Moon, secretary-general of the United Nations, argued that the war had begun "as an ecological crisis, arising at least in part from climate change."
Moon noted that some scientists believe that the rise in Indian Ocean temperatures associated with global warming may have been responsible for drought conditions afflicting Sudan. The droughts, in turn, caused a breakdown in relations between nomadic Arab groups and settled black farmers. Before the drought, both groups had shared the same wells and camels had grazed freely. But as the drought intensified, the farmers fenced their lands, fearing that grazing would damage their crops and deplete their water. It was this conflict over resources, Moon argues, that precipitated the civil war.
If Moon is right, Darfur demonstrates graphically two major points about climate change. First, the effects of global warming are extremely hard to predict. And second, whatever those effects are, they will hit those regions with the least resources hardest. Places like the United States, with more resources and stable governments, have some room to maneuver in adjusting to global warming. In places like Sudan, however, a change in climate can spiral quickly into a political and humanitarian catastrophe.
years, the region frequently experienced droughts that lasted decades or even centuries. The researchers also discovered that fluctuations in dryness over the centuries seemed to be related to variations in sea surface temperature. There is, therefore, concern that global warming could tip the region back into a period of extreme drought. In a 2009 article, Overpeck is quoted as saying, "Clearly, much of West Africa is already on the edge of sus-tainability . . . and the situation could become much more dire in the future with increased global warming."20
Another region that may already be experiencing a shift to a drier climate is the American Southwest. There is "broad consensus amongst climate models that this region will dry significantly in the twenty-first century, and that the transition to a more arid climate are already under way. If these models are correct . . . the levels of aridity in the recent multi-year drought, or the Dust Bowl and the 1950s droughts, will, within the coming years to decades, become the new climatology of the American Southwest," according to Columbia University researcher Richard Seager. Seager noted that the United States is wealthy enough that the drought may not cause massive loss of life the way that comparable dry spells have in Africa. He noted, however, that in Western nations irrigation systems and pumps are used widely to bring water vast distances and allow people to live in dry regions that would normally be uninhabitable. Seager warns, "Plumbing on a continental scale supports massive agricultural, industrial and cultural production. Just how vulnerable is such a complex, water-dependent society in an arid region to climate? We do not know. . . . But, as man changes the climate, we may be about to find out."21
There are numerous ways in which higher temperatures may contribute to drought. The first is by reducing precipitation. As mentioned earlier, high temperatures usually mean more rainfall. The effect can vary regionally, however. For example, environmental photojournalist Gary Braasch, in his book Earth Under Fire, notes that lower rainfall in southern Africa from the late 1970s to today may be related to "higher sea surface temperatures in the Indian Ocean," perhaps caused by global warming.22 Catherine Gautier notes that models also "predict a widespread decrease in mid-latitude summer precipitation except in eastern Asia, as well as a decrease in precipitation over many subtropical areas."23
Even if rainfall does not decrease, however, some regions may still become drier. This is because of evaporation. As temperatures rise, water turns to water vapor more quickly. "The higher evaporation rates will lead to greater drying of soils and vegetation, especially during the warm season."24 Thus, for example, evaporation rates contributed to the 2002 drought in Australia. A study by the World Wildlife Fund-Australia examined both the 2002 drought and four other droughts since 1950 and concluded that "higher temperatures caused a marked increase in evaporation rates from soil, watercourses, and vegetation."25 Because there was more evaporation, the drought was more severe, creating a greater danger of brushfires and reducing agricultural productivity.
Increased evaporation rates could have a profound effect on such climates as the Amazon rain forest. "Ultimately, the rain forests in Amazonia are there because the rainy season is so dependable from year to year, and average temperatures, though hot, are not hot enough to evaporate critical amounts of water out of soaked soils," according to University of California-Berkeley paleontologist Anthony D. Barnosky in his book Heatstroke.26 Barnosky looks specifically at the rainforest in Tambopata, Peru, which receives 80 to 100 inches (2,000-2,500mm) of rain per year, so that the soil is basically always wet. If temperatures rise, however, evaporation will happen more quickly, and the ground may become drier. "Dry those soils enough," Barnosky says, "and what used to be rainforest becomes savannah [a tropical grassland with only scattered trees] ."27
Thus, because of increased evaporation, climates may become drier in certain regions even if rainfall stays the same. By the same token, rainfall increases in some regions may create wetter climates despite higher temperatures and increased evaporation. Because so many complicated factors are involved—rainfall, ocean temperature, cloud cover, evaporation—no one can say for certain that any particular change in a climate is caused by global warming. But scientists do know that, as the earth warms, patterns of precipitation and evaporation will change in ways that will affect everyone, from Bangladesh to Peru.
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