Climatic change: Desert-forming processes

Several different hypotheses exist in which atmospheric dust is identified as having a dominant role in desert-forming processes. The theory of Bryson and Baerreis for the Rajasthan Desert of northwest India—where increased atmospheric dust was postulated to be responsible for enhanced infrared radiative divergence of the upper air that accelerated cooling aloft and increased subsidence that suppressed convective precipitation and the release of monsoon moisture—is shown to be in harmony with current assessments of climatic effects of atmospheric dust. On the other hand, current ideas of dust effects tend to negate the more recent theory of Bryson concerning the Sahelian drouth, where global effects of both increased atmospheric dust and CO 2were hypothesized to be responsible for a southward shift of the Hadley-Rossby transition zone of descending air that also tended to reduce rainfall. Thus, correct knowledge of climatic effects of atmospheric dust appears essential to our understanding of desert-forming processes.