By Sid Perkins
By the end of this century, the world’s hottest desert will be even hotter. The
Sahara will also be smaller and drier than it is now, according to an
international team of climate modelers.
The Sahara stretches the full width of northern Africa and now covers an area the
size of the United States. But that area isn’t constant: It can swell and shrink
significantly in response to long-term weather patterns, says Gerald A. Meehl, a
climate modeler at the National Center for Atmospheric Research in Boulder, Colo.
For example, an extended drought along the southern boundary of the desert in the
1970s led to its expansion there in the 1980s.
Overall, the portion of the Sahara that gets less than 50 millimeters of rain per
year–a region that has almost no vegetation–expanded from the 1950s to the 1990s.
However, Meehl and his colleagues predict that that trend will reverse in the
present century. The researchers report their results in the July 15 Geophysical
Research Letters.
The team’s computer simulations predict that rainfall will increase in the
southwestern portions of the desert. By 2090, the desert will shrink back to
occupy an area about the same size that it covered in 1900, says Meehl. Even so,
the model predicts that average annual rainfall elsewhere in the Sahara then will
be about 2 mm lower than the average recorded there between 1961 and 1990.
The decreased rainfall in the desert will probably lead to reduced vegetation.
This, in turn, will cause the terrain to absorb more solar radiation, which will
accentuate any increase in global temperature, Meehl explains. Although the team’s
climate model predicts a 2C rise in average global temperature by the end of the
century, it suggests that average temperatures in the Sahara should rise by about
2.8C.
