From the BBC programme (which Im not going to say is correct, Id much rather first check with more climatologists if this is correct, since the subject has not received nearly as much press as global warming), explaining the possibilities of Air pollution in the northern hemisphere affecting rainfall in East Africa..... it is possible that its simply a natural phenomenon of course, but good science means investigating all possibilities
The 1984 Ethiopian famine shocked the world. It was partly caused by a decade's long drought right across sub-Saharan Africa - a region known as the Sahel. For year after year the summer rains failed. At the time some scientists blamed overgrazing and poor land management. But now there's evidence that the real culprit was Global Dimming. The Sahel's lifeblood has always been a seasonal monsoon. For most of the year it is completely dry. But every summer, the heat of the sun warms the oceans north of the equator. This draws the rain belt that forms over the equator northwards, bringing rain to the Sahel. But for twenty years in the 1970s and 80s the tropical rain belt consistently failed to shift northwards - and the African monsoon failed. For climate scientists like Leon Rotstayn the disappearance of the rains had long been a puzzle. He could see that pollution from Europe and North America blew right across the Atlantic, but all the climate models suggested it should have little effect on the monsoon. But then Rotstayn decided to find out what would happen if he took the Maldive findings into account.
DR LEON ROTSTAYN (CSIRO Atmospheric Research): What we found in our model was that when we allowed the pollution from Europe and North America to affect the properties of the clouds in the northern hemisphere the clouds reflected more sunlight back to space and this cooled the oceans of the northern hemisphere. And to our surprise the result of this was that the tropical rain bands moved southwards tracking away from the more polluted northern hemisphere towards the southern hemisphere.
NARRATOR: Polluted clouds stopped the heat of the sun getting through. That heat was needed to draw the tropical rains northwards. So the life giving rain belt never made it to the Sahel.
DR LEON ROTSTAYN: So what our model is suggesting is that these droughts in the Sahel in the 1970s and the 1980s may have been caused by pollution from Europe and North America affecting the properties of the clouds and cooling the oceans of the northern hemisphere.
From the YOUTUBE series on Global Dimming posted above... here is the script, I must admit, BBC is the only source that I have heard of it, I tend to take them a bit more serious than most networks, which is why I note this for discussion: http://www.bbc.co.uk/sn/tvradio/programmes/horizon/dimming_trans.shtml