[I]"By way, anyone know if it is true what environmentalists say about desertification and the Middle East? I heard one guy saying that in the Roman period, Egypt was described as the Empire's bread basket and arguing that over-cultivation, deforestation etc dramatically reduced the productivity of the land. Any truth to this or is it a myth? It's a rather dramatic illustration of the perils of environmental degradation if true."

This is true. The worst example is the environmental degredation of ancient mesopotamia (mostly modern Iraq & parts of Iran) where agriculture was first invented. Many historians believe salinization from overirrigation etc. was largely responsible. This region supported the earliest and highest civilization in the world for thousands of years before the Christian era. By the time of Rome, Babylon and the other ancient cities had fallen into such total ruins that they were completely forgotten until archeologists began excavating and decyphering their inscriptions in the 19th century. So forgotten were these cities that local peasants whose families had lived in the region for more than 1000 years were astonished when the ruins were uncovered by archeologists.

As for north africa, it was temperate during the last ice age which ended about 6,500 B.P. and the early bronze age, but not since before the Roman era. Those cave and rock paintings you're talking about are generally a lot older than the pyramids, especially the ones showing hippos wallowing in marshlands.