Curt Stager, a scientist at Paul Smiths College, is publishing an article later this month in the journal Science that describes an ancient drought that transformed Asia and Africa thousands of years ago.
The "H1 mega-drought" may have wiped out whole tribes of humans, as it dried up rivers and lakes across whole continents.
As Brian Mann reports, Stager thinks that devastating event could be a warning for people living in a new period of global warming.
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Twenty-five years ago, Curt Stager was paddling the waters of Lake Barombi Mbo in Cameroon.
He and other researchers had rigged a crude drilling platform – not searching for oil, but rooting around for the deep layers of muck that have been settling on the bottom of the lake for millenia.
"We built the raft," Stager recalled. "We strung 10 foot long sections of pipe together…it plunges into the bottom of the lake. We ended up getting twenty-something thousand years worth of sediment."
These days, much of Cameroon is cloaked in rain forest. But down under all that lake mud Stager found sediments that showed that this African landscape has changed dramatically.
"You bore on down through this wet brown mud. Suddenly you hit shells and sand and soil. Which means that it would have looked like a beach and before that it would have looked like the Serengeti Plains.
Stager is a paleo-climatologist at Paul Smiths College in the Adirondacks. He studies the history of the really big climate patterns that have shaped our planet over thousands of years.
When scientists were collecting those ancient sediment samples from lakes across Africa and Asia, he says they weren’t really sure what it would all mean.
But in a new paper set to be published next month in the journal Science, Stager argues that he’s found evidence of a massive drought, so big that it literally changed the world.
Sixteen thousand years ago, the Monsoons of Asia failed. The Nile and the Congo shriveled up. The great lakes of Africa and the Near East turned to dust.
"There would have been nowhere [for tribes of humans] to go," he said. "It would have turned what is now a green part of Africa into a savannah or a desert."
Normally this might just sort of be cool information, a time-machine glimpse of the harsh world faced by our ancient ancestors.
But Stager’s paper makes one more connection.
He says this mega-drought, which lasted for centuries, was likely caused by a natural cycle of global warming, the end of an ice age that melted glaciers and tipped thick ice sheets into the North Atlantic.
"Somehow the oceans not only cooled in the North Atlantic, but it looks like all through the Indian Ocean, too, and that’s probably why the rains were shut off in the tropics," he said.
These days, scientists are seeing a similar warming pattern in the North Atlantic, triggered not by the end of an ice age this time, but by industrial greenhouse gases.
Once again, the two-mile thick ice sheet in Greenland is melting fast.
"From what we’ve seen in this one glacier and other ones like it in Greenland, there’s been just such rapid enormous changes in the last five or ten years," said glaciologist Gordon Hamilton from the University of Maine, speaking with CNN. "It’s really been quite alarming.
Curt Stager doesn’t think this round of global warming will trigger the kind of devastating disruption in ocean currents and rains that our ancestors faced.
For one thing, the amount of ice in the North Atlantic is far smaller now.
But he says the mega-drought sixteen thousand years ago shows that rapid warming in the arctic might trigger sudden and dramatic changes all over the planet, possibly occurring in a single lifetime.
"Abrupt, severe climate change really can happen, because it did," Stager said. "We know tipping points like this exist. The big mystery is where is the tipping point?"
Stager points out that even a much smaller disruption to global rain patterns could have huge implications – especially now when the human population in places like Cameroon is so much greater.
"It would be unbelievable. More than half of humankind lives in the zones that were affected by this," he said.