Past shows future
A study by the Massachusetts Institute of Technology provides evidence of a radical climate change 118,000 years ago. This climate change may also allow conclusions to be drawn about the future of the earth. According to Scott Lehman of the Institute for Arctic and Alpine Research at the University of Colorado at Boulder, the study, published in Nature (November 13 issue), suggests there may be a rapid reduction in global ocean circulation around 118,000 years ago the youngest ice age on earth could have started. Lehman is the author of a News and Views article commenting on the importance of this study, led by Jess Adkins. The team from the Massachusetts Institute of Technology examined a sediment drill core from the ocean floor using geochemical dating methods. The drill core was approximately 45 m long and came from the North Atlantic Sargasso Sea. It contained 160,000 year old sediments and fossils and testified to significant chemical changes in the deep sea during the last 400 years of the most recent interglacial period, which began about 127,000 years ago and ended about 118,000 years ago.
The study indicates that the circulatory current that now carries oceanic heat northward from the tropics and warms much of Europe remained strong and unchanged for most of the interglacial period. "Interestingly, evidence was also found that the incipient growth of ice masses, marking the end of the interglacial period, was accompanied by a sudden reversal in ocean circulation that lasted only 400 years and from which the climate system apparently never recovered," wrote Lehman in Nature.
According to Lehman, scientists still don't know why or how this might have happened."Some climate formation scenarios suggest that warming temperatures on Earth have 'stalled' ocean circulation through melting ice sheets and increased precipitation." Climate models that account for rapidly increasing levels of carbon dioxide in the Earth's atmosphere suggest that the greenhouse gas is likely accelerating the warming process.
Earth temperatures have been relatively high and stable for most of the current interglacial period, which began about 9000 years ago. A well-known exception is the "Little Ice Age" during which the North Atlantic region cooled, beginning about 1500 years ago and lasting for several hundred years.
All the time, semi-permanent snowfields blanketed Labrador and Baffin Island, increasing reflection of sunlight from Earth back into the atmosphere. Furthermore, for some time the solar radiation hitting the earth decreased, the strength of which changes together with a periodic oscillation of the earth's axis. According to Lehman, this decrease is also evident today.
"In this context, a slight slowdown in ocean circulation can be likened to the action of a sledgehammer and conceivably bring the current interglacial period to its knees," wrote Lehman. "This possibility raises concerns about the potential impact of the enhanced greenhouse effect on the oceans."
Lehman sees a particular problem in the fact that scientists do not know what is natural about the current climate change and what is caused by humans. This question will only be answered with additional research.
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