G&G Community: Wade's Work Shows a Reverse Greenhouse Effect

by Keith Randall

09/15/09 - Geologist Bridget Wade has helped uncover a mystery regarding formation of the Antarctic ice cap 34 million years ago, and for the first time, has shown a relationship of how declining carbon dioxide levels contributed to accumulations of the ice there – in effect, a reverse of the “greenhouse effect.”

Bridge Wade in the mudBridget Wade, a professor of geology and geophysics, is part of a team that includes researchers from England’s Bristol and Cardiff Universities and has its work published in the current issue of Nature magazine.

Scientists have long thought ice accumulations began 34 million years, and the researchers unraveled the mystery in an unusual way – by examining fossils found in East Africa. Declining levels of carbon dioxide in the Earth’s atmosphere was the trigger mechanism for the cooling trend and subsequent ice formation, the Texas A&M geoscientist says.

“The link of carbon dioxide was the opposite of what we now call the ‘greenhouse effect,’ ” she says in explaining the five-year project.

“It led to a much colder climate and enabled the ice to form in the Antarctic. We believe this is the first time that such a link has been found between ice increase and declining carbon dioxide levels.”

Wade says geologists have previously suspected the formation of the ice cap in the Antarctic was caused by a gradually diminishing greenhouse effect, but had never before made a direct link. The period at the time – called the Eocene-Oligocene – culminated in the development of the large ice sheets that still remains in the Antarctic.

The team drilled cores containing very well-preserved microfossils in Tanzania and discovered key sediments near a small African village. The shell-like fossils in these cores provided the critical information needed to prove their findings.

Wade says the results could offer important keys for future research and will contribute to knowledge currently being assembled about the Earth’s atmosphere now compared to millions of years ago.

“This was the biggest climate switch since the extinction of the dinosaurs about 65 million years ago,” she points out.

“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 it confirms the relationship between carbon dioxide levels in the atmosphere and global climate changes.

“The next step is to do some climate modeling,” she adds. “We know carbon dioxide levels have changed, but we need to learn how they have changed and what it could mean for us in the future.”

The study was funded by the United Kingdom’s National Environmental Research Council. To view a video of Wade click here.

 
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