Africa: The next megadrought
By Dennis T. Avery
Africa is suffering serious drought again -- in both the Horn of Africa (Somalia, Ethiopia, and Kenya) and in West Africa's Mali. How bad is the drought likely to get?
Three years ago, the New York Times reported a study of the lakebed sediments in Ghana's Lake Bosumtwi. Lead author Tim Shanahan of the University of Texas said Africa gets serious drought every 30 to 65 years -- but "changing Atlantic sea-surface temperatures" are capable of triggering "much longer and more severe future droughts."
The Bosumtwi mud revealed a West African megadrought during the Little Ice Age that lasted from 1400 to 1750! The trunks of ancient dead trees now submerged in deep water show the lake lost four times as much water in the Little Ice Age as in the severe Sahel droughts of the 70's. Meanwhile, Africa's population has expanded from 110 million to 1 billion in the intervening centuries.
It gets worse. In East Africa, Karl Butzer of Switzerland found long wet-dry cycles in Ethiopian valley sediments during the "little ice age" called the Dark Ages. The culture collapsed in AD 600 and did not re-emerge until more than 600 years later.
Fast forward to 2011 when University of Washington's oceanographer Julian Sachs' article, "A Shifting Band of Rain" appeared in Scientific American. He studied the Intertropical Convergence Zone, the tropical rainbelts near the equator. Lakebed sediments across a whole north-south range of Pacific islands show him that the tropical rains have moved north 550 km in the years since the Lake Bosumtwi megadrought.
Sachs predicts the rain belt could move another 550 km north in the centuries ahead, as the Modern Warming continues. The Mexican desert could come to the southern U.S. The rains that now support farming in Ghana and Ethiopia could move north to the Sahara and North Africa, as they did during the Roman Warming (200 BC–AD 600). The Roman Empire fed itself on grain from then-wetter North Africa and Egypt -- while Ghanaians and Ethiopians starved or moved. Came the Dark Ages and the ITCZ moved south again, while both North African and Egyptian cultures collapsed for centuries.
Shanahan is describing the effects of the 1,500-year Dansgaard-Oeschger cycle, discovered in the Greenland ice cores in 1984. He referred to "changing North Atlantic sea-surface temperatures" -- but he's really talking about a solar-driven cycle that has produced more than 500 global warmings and "little ice ages" in the past million years. Our study of paleoclimate proxies is only now getting good enough to show us the drastic climate consequences of the shifting rain belts.
Is Africa starting the next megadrought now? I think that unlikely. We're only 150 years into the Modern Warming and even the short Medieval Warming lasted 350 years. It is more likely a repeat of the 1970s "serious drought" that cost 100,000 lives.
What will the world do when the tropical rains leave sub-Saharan Africa sometime in the centuries ahead for several hundred years, leaving behind many millions of Africans who will not be able to walk to sustainability? Ditto for Latin America. Where would we put them and how would we get them there?
Human numbers will be declining naturally after 2050 -- but mid-Africa's population may double before it stabilizes. Organic or traditional primitive farming won't feed them, or protect Africa's unique wild species from the stew pots of the starving.
During the famines of the Little Ice Age, human ingenuity produced the gang plow to crop the heavy, rich soils of the valleys that had defied earlier plows. "New" crops brought by Spanish ships from the New World included the potato, the tomato, maize and sweet potatoes -- radically increasing food yields per acre for both Europe and Africa. Industrial nitrogen fertilizer is currently feeding 5.5 billion of our fellow humans. We'll need all our inventiveness and our persistence to adapt in the earth's future droughts; and enlightened consensus to then accept the technology.