Some meteorologists have insisted that the severity of the drought in sub-Saharan West Africa and its long duration (nearly 40 years to date) must be a sign of a long-term alteration in climate. Among the theories proposed to explain this change, one hypothesis that has gained widespread attention attributes the drought to north, and so have to pass through more dust-laden atmosphere on the way to the Earth.
Since winds are set in motion by differences in air pressure caused by unequal heating of the atmosphere, supporters of the cooling hypothesis have argued that a growing temperature differential between the unusually cool middle and high latitudes and the warm tropical latitudes is causing a southward expansion of the circumpolar vortex—the away from the Earth, to further cooling, and, indirectly, to further drought in sub-Saharan West Africa.
Despite these dire predictions, and even though the current African drought has lasted longer than any other in this century, the notion that the drought is caused by cooling of the Northern Hemisphere is, in fact, not well supported. Contrary to the predictions of the cooling hypothesis, during one period of rapid well as land are taken into account, the Northern Hemisphere may not have cooled at all.
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Answers that are plausible or likely but not actually guaranteed by the text.
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