April 19, 2009
Africa Experiences Recurring Long Big Droughts

Andrew Revkin of the New York Times reports on a recent study that found part of Africa went thru a drought that started in the 1400s and lasted over 3 centuries until 1750.

For at least 3,000 years, a drumbeat of potent droughts, far longer and more severe than any experienced recently, have seared a belt of sub-Saharan Africa that is now home to tens of millions of the world’s poorest people, climate researchers report in a new study.

The last really long drought in Africa occurred while Europe was going thru its Little Ice Age cold period.

The last such drought, persisting more than three centuries, ended around 1750, the research team writes in the April 17 issue of the journal Science.

Future big long-lasting droughts in Africa are inevitable (assuming no climate engineering). They are a natural occurrence. But human pollutants might make them occur more often and more severely.

Humans have inadvertently caused severe climate change in the past. The diseases brought from Europe to the Americas by Spanish and Portuguese explorers caused the collapse of the Aztec and Inca empires. The empire collapses caused abandoned farmland to revert to forests, sucking CO2 out of the atmosphere and probably helping to trigger the Little Ice Age. That cooling caused a big increase in food prices in Europe and lots of disease and starvation. Perhaps that cooling also caused (or at least contributed to) the multi-century dry spell in Africa.

The Western hemisphere is not immune from big climatic shifts. North America has also experienced century-long droughts over the last 7000 years.

Climate changes naturally. Climate is not naturally stable. Since humans harness a very substantial and increasing portion of all the world's biomass our margin for handling severe natural changes is shrinking by some measures. We would have a harder time tapping into a larger portion of the world's biomass if the total biomass shrunk for some (man-made or natural) reason. On the other hand, we do have more technology to use to buffer the effects of climate change on us - at least those of us who live in industrialized countries.

Some day when climate changes due to natural long term processes, human pollutants, volcanic eruptions, or a massive asteroid strike if you are still around don't be shocked. We've been living through a period of relatively less severe climate change. Unless we develop the ability and willingness to control long term climate trends this period of relative stability will end some day.

Update: An excellent February 2008 National Geographic article "Drying of the West" explores past, present, and future dry spells in the US West.

Stine found drowned stumps in many other places in the Sierra Nevada. They all fell into two distinct generations, corresponding to two distinct droughts. The first had begun sometime before 900 and lasted over two centuries. There followed several extremely wet decades, not unlike those of the early 20th century. Then the next epic drought kicked in for 150 years, ending around 1350. Stine estimates that the runoff into Sierran lakes during the droughts must have been less than 60 percent of the modern average, and it may have been as low as 25 percent, for decades at a time. "What we have come to consider normal is profoundly wet," Stine said. "We're kidding ourselves if we think that's going to continue, with or without global warming."

Share |      Randall Parker, 2009 April 19 05:35 PM  Climate Trends


Comments
Assistant Village Idiot said at April 19, 2009 7:38 PM:

This is much of Ruddiman's conclusion in Plows, Plagues, and Petroleum.

JAY said at April 20, 2009 5:40 AM:

Future big long-lasting droughts in Africa are inevitable (assuming no climate engineering). They are a natural occurrence. But human pollutants might make them occur more often and more severely. Or less often and less severely.

trichards said at April 20, 2009 8:27 AM:

Randall

Wowzers at that first big paragraph about human diseases leading to second ice age. Wowzers wowzers wowzers. Big think science baby. LOL

Tom said at April 20, 2009 1:39 PM:

"Perhaps that cooling also caused (or at least contributed to) the multi-century dry spell in Africa."

Probably not the cause - the article says that the droughts started around 1400, which would be almost 100 years prior to Columbus.

The case for the Little Ice Age seems somewhat stronger. Wikipedia lists these events as possible starts of the little ice age:

* 1250 for when Atlantic pack ice began to grow
* 1300 for when warm summers stopped being dependable in Northern Europe
* 1315 for the rains and Great Famine of 1315-1317
* 1550 for theorized beginning of worldwide glacial expansion (post-Columbian, but not by much)
* 1650 for the first climatic minimum

Maybe there's some effect here - 1550 would be about 30 years after the first major smallpox outbreak (again, per Wikipedia). There could have been some reforestation in this time, though probably not a ton.

Matthew said at April 21, 2009 4:52 PM:

http://www.donatebot.com/

Donatebot allows anyone to exchange computer cycles for water, food, education, or trees. I am currently doing education and trees have the lowest number of donations.

Maybe anyone who bothers to read this comment can sign up, and simply post back here saying so!

-Matthew (cognitive science student at UTD)

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