The Parallel Climate Model (PCM) Version 1.1 simulates a reasonable twentieth century climatology in the Sahara Desert. From late 1940s to the end of 1980s, the simulated Sahara Desert, bounded by the 50 mm mean annual rainfall isoline, becomes larger and shifts eastward. The model produces a decreasing rainfall trend while the surface temperature and meridional boundaries are almost stable. In the usual scenario with increasing greenhouse gases from the 1980s to the 2090s the Sahara becomes smaller, moves north and west and continues to dry. Both the size change and latitudinal shift show a century long trend. Compared to 1961--90 climatology, the average northward shift is around 1¿ and the surface temperature about 2.8 ¿C warmer to the end of 21st century. The local greenhouse effect may cause such warming trend. ¿ 2001 American Geophysical Union