Researchers have confirmed for the first time a link between declining levels of atmospheric carbon dioxide (CO2) and the formation of Antarctic ice caps some 34 million years ago.
The results of the major research study support computer climate models that predict both the creation of ice sheets when CO2 levels fall and the melting of ice caps when CO2 levels rise.
“Our study is the first to provide a direct link between the establishment of an ice sheet on Antarctica and atmospheric carbon dioxide levels and therefore confirms the relationship between carbon dioxide levels in the atmosphere and global climate,” said Bridget Wade from Texas A&M University, the study’s co-author.
Geologists have long speculated that the formation of the Antarctic ice sheets was caused by a slowly diminishing natural greenhouse effect.
The team of scientists, from Cardiff, Bristol and Texas A&M universities, traveled to the remote East Africa village of Stakishari to extract microfossils from rock samples that showed the atmospheric CO2 levels during the time of the formation of the Antarctic ice cap. The area was known to contain deposits of a particular type of well-preserved microfossil that can reveal past CO2 levels.
Accompanied by an armed guard to protect them from lions, the researchers spent weeks in the African bush in Tanzania gathering samples, then used them to reconstruct CO2 levels around the time of the Eocene – Oligocene climate transition.
“There are no samples of air from that age that we can measure, so you need to find something you can measure that would have responded to the atmospheric CO2,” explained Professor Paul Pearson from Cardiff University during an interview with Reuters.
The study’s results confirmed that the Antarctic ice sheet began to form when atmospheric CO2 levels reached a tipping point of around 760 parts per million — about double current levels.
“About 34 million years ago the Earth experienced a mysterious cooling trend. Glaciers and small ice sheets developed in Antarctica, sea levels fell and temperate forests began to displace tropical-type vegetation in many areas,” said Professor Pearson, who led the mission to Stakishari.
“The period, known to geologists as the Eocene – Oligocene transition, culminated in the rapid development of a continental-scale ice sheet on Antarctica, which has been there ever since.
“We therefore set out to establish whether there was a substantial decline in atmospheric carbon dioxide levels as the Antarctic ice sheet began to grow.”
The scientists mapped vast areas of bush and wilderness, and pieced together the underlying local rock formations using occasional outcrops of rocks and streambeds.
They discovered sediments of the right age near Stakishari, where they assembled a drilling rig and extracted hundreds of meters of samples from under the ground. Eventually they were able to obtain precisely the piece of Earth’s history they had been searching for.
“By using the rather unique set of samples from Tanzania and a new analytical technique that I developed, we have, for the first time, been able to reconstruct the concentration of CO2 across the Eocene-Oligocene boundary – the time period about 34 million years ago when ice sheets first started to grow on Eastern Antarctica,” said Dr. Gavin Foster from the University of Bristol Earth Sciences Department, the study’s co-author.
“This was the biggest climate switch since the extinction of the dinosaurs 65 million years ago,” said Wade.
The findings come just months ahead of an important U.N. Climate Conference in Copenhagen later this year, which seeks to reach a consensus on a successor treaty to the Kyoto Protocol.
The study was published online in the journal Nature.
Images Courtesy Paul Pearson/Cardiff University
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