We used 18 years (1979--1992 and 1997--2000) of aerosol observations from TOMS satellites to monitor the inter-annual variability of summertime atmospheric dust optical thickness over both Atlantic and Africa. A comparison of TOMS dust optical thicknesses with ground-based Sun-photometer measurements shows that our long-term data set is consistent in time and space and is thus suitable for studying the interannual and decadal variability of African dust transport. Our results show that dust emissions in North western Sahel are so variable from one year to the other that they control most of the variability of summer dust transport to the tropical Atlantic. Our satellite data also demonstrate that there is a large scale correlation between Atlantic dust export and Sahel drought during the previous year, which suggests that dust emissions in this semi-arid region are likely controlled by the position of the vegetated southern boundary of the Sahara.