This is not actually correct. They found a 1.5 K cooling averaged over
a 30 year period. I am not an expert in their science, so don't know
what the error bar is on this, but this does not preclude a very large
cooling for 5 years which could have been catastrophic.
Alan Robock
Alan Robock, Distinguished Professor
Editor, Reviews of Geophysics
Director, Meteorology Undergraduate Program
Associate Director, Center for Environmental Prediction
Department of Environmental Sciences Phone: +1-848-932-5751
Rutgers University Fax: +1-732-932-8644
14 College Farm Road E-mail: [email protected]
New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock
http://twitter.com/AlanRobock
On 5/3/2013 9:43 PM, Andrew Lockley wrote:
http://m.pnas.org/content/early/2013/04/24/1301474110
Ash from the Toba supereruption in Lake Malawi shows no volcanic
winter in East Africa at 75 ka
Abstract
The most explosive volcanic event of the Quaternary was the eruption
of Mt. Toba, Sumatra, 75,000 y ago, which produced voluminous ash
deposits found across much of the Indian Ocean, Indian Peninsula, and
South China Sea. A major climatic downturn observed within the
Greenland ice cores has been attributed to the cooling effects of the
ash and aerosols ejected during the eruption of the Youngest Toba Tuff
(YTT). These events coincided roughly with a hypothesized human
genetic bottleneck, when the number of our species in Africa may have
been reduced to near extinction. Some have speculated that the demise
of early modern humans at that time was due in part to a dramatic
climate shift triggered by the supereruption. Others have argued that
environmental conditions would not have been so severe to have such an
impact on our ancestors, and furthermore, that modern humans may have
already expanded beyond Africa by this time. We report an observation
of the YTT in Africa, recovered as a cryptotephra layer in Lake Malawi
sediments, >7,000 km west of the source volcano. The YTT isochron
provides an accurate and precise age estimate for the Lake Malawi
paleoclimate record, which revises the chronology of past climatic
events in East Africa. The YTT in Lake Malawi is not accompanied by a
major change in sediment composition or evidence for substantial
temperature change, implying that the eruption did not significantly
impact the climate of East Africa and was not the cause of a human
genetic bottleneck at that time.
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