Worldwide shipments of frankincense to markets as far away as China and Rome could have started at Ubar. In the end, it was victimized by politics, economics and climate after a drop in demand for the frankincense fragrance as Christianity preached burying bodies instead of burning them. The abandoned villages of Ad eventually were inundated by tides of shifting sands, and eventually dunes reaching heights of 200 to 600 feet. The world's largest desert fluctuated in size during the 1980s, according to a NASA study of observation-satellite data. Desert fluctuations depended on the amount and distribution of the rainfall in the area.
Rainfall controls the amount of vegetation seen from space.
Scientists suggest changes in global desert area may be tied to global climate changes. The Atlas Mountains and Mediterranean Sea make up a nearly immovable northern boundary, but the Sahara's southern boundary moved south 80 miles between 1980 and 1990. After moving to the south between 1981 and 1984, the Sahara retreated northward 88 miles from 1985 to 1986. However, it migrated 34 miles south in 1987. The southern boundary retreated 62 miles to the north in 1988, then expanded 46 miles to the south in 1989 and 1990.