Tear down those pyramids, they caused it.
It was the goats. They ate everything green until nothing was left but the sand.
Want to make the Sahara green again? Fine. Prevailing westerly winds blow across northern Africa. By using this natural feature, a string of thorium-powered nuclear reactors set up on the shores of the Red Sea and the Horn of Africa, and used to desalinate vast quantities of ocean water by evaporation of the seawater to concentrated brine, then condensing the water vapor produced and collecting it as potable water, and using huge pumps to deliver the water for irrigation across western Egypt, Libya, Algeria, and Morocco, the desert could once again be turned green. As a self-fulfilling spread of surface and atmospheric moisture expands across the northern tier of the Sahara, lakes and ponds will form, the moisture used again and again for the propagation of plant life as it is transpired, condensed in clouds, and falls yet further to the west as rain.
That is, if there is any will whatsoever to actually transform the climate. The politics of the area (heavy Muslim population with no understanding of the underlying physics or economics) would set about destroying this degree of engineering and climate control, if for no other reason than it would wrought vast change in a region where change is fiercely resisted.
Chariots with horses to be phased out by before next dynasty to be replaced by cleaner, nicer Mules with renewable travois technology. So let it be written...