news@lboro (2009)
2011
Scientists look to the past to consider future potential climate change
March 10, 2011
Climate change could become worse than anything we've seen in recorded history, according to results of a study that has appeared in the journal Science.
An international team of scientists – led by Curt Stager of Paul Smith's College, New York, and involving David Ryves from Loughborough University – has compiled over forty ‘palaeo-climatic’ records across Africa and Asia (looking at climate change in the context of the last several thousand years of earth’s history), including sediment cores from Lake Victoria and Lake Tanganyika, both in Africa.
The records show that one of the most widespread and intense droughts of the last 50,000 years or more struck Africa and Southern Asia 17,000 to 16,000 years ago.
Between 18,000 and 15,000 years ago, large amounts of ice and meltwater entered the North Atlantic Ocean, causing regional cooling but also major drought in the tropics, according to Paul Filmer, programme director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research along with NSF's Division of Atmospheric and Geospace Sciences and its Division of Ocean Sciences.
"The height of this time period coincided with one of the most extreme megadroughts of the last 50,000 years in the Afro-Asian monsoon region with potentially serious consequences for the Paleolithic humans that lived there at the time," says Filmer.
The ‘H1 megadrought’, as it is known, was one of the most severe climate trials ever faced by anatomically modern humans, and at a time when humans in northern latitudes were experiencing extreme cold.
“Evidence from diatoms (microscopic algae) preserved in the sediments from Lake Victoria show that the lake salinity rose as water levels fell”, says David Ryves, co-author of the Science paper. Africa's Lake Victoria, now the world's largest tropical lake, dried out, as did Lake Tana in Ethiopia, and Lake Van in Turkey. The Nile, Congo and other major rivers shrivelled, and Asian summer monsoons weakened or failed from China to the Mediterranean, meaning the monsoon season carried little or no rainwater.
What caused the megadrought remains a mystery, but its timing suggests a link to a massive surge of icebergs and meltwater into the North Atlantic at the close of the last ice age, known as Heinrich Event 1 (or ‘H1’).
Previous studies had implicated southward drift of the tropical rain belt as a localized cause, but the broad geographic coverage in this study paints a more nuanced picture.
"If southward drift were the only cause," says Curt Stager, lead author of the Science paper, "we'd have found evidence of wetting farther south. But the megadrought hit equatorial and southeastern Africa as well, so the rain belt didn't just move, it also weakened."
Climate models have yet to simulate the full scope of the event. The lack of a complete explanation opens the question of whether an extreme megadrought could strike again as the world warms and de-ices further.
However, Stager says, "There's much less ice left to collapse into the North Atlantic now, so I'd be surprised if it could all happen again, at least on such a huge scale."
The co-authors of the paper were David Ryves of Loughborough University; Brian Chase of the Institut des Sciences de l'Evolution de Montpellier (France) and the Department of Archaeology, University of Bergen (Norway); and Francesco Pausata of the Geophysical Institute, University of Bergen (Norway).
The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2010, its budget is about $6.9 billion. NSF funds reach all 50 states through grants to nearly 2,000 universities and institutions. Each year, NSF receives over 45,000 competitive requests for funding, and makes over 11,500 new funding awards. NSF also awards over $400 million in professional and service contracts yearly.