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   from the issue of February 1, 2007

Research eyes climate shifts, instability at end of last Ice Age


Research Focus - A regular Scarlet feature highlighting research projects at UNL


As carbon dioxide levels in Earth's atmosphere continues to rise, new geological evidence suggests the planet could begin to experience climatic instability unlike anything seen in the last 34 million to 40 million years.

Writing in the Jan. 5 issue of the international journal Science, a team of scientists that includes four current and former UNL researchers, reported finding evidence of repeated major climate changes during the period when Earth last came out of a major ice age.

In a multi pronged study of the period from 305 million to 265 million years ago, the scientists found evidence of several major climate shifts, alternating between extreme cold, (glacial periods) and periods of relative warmth. In each instance, an increase in atmospheric carbon dioxide accompanied a shift to a warmer climate and decrease in CO2 accompanied a shift to a glacial climate.

"What's considerably different from previous perceptions of this ice age is that we see evidence that there were periods of really austere glacial climate that alternated with periods of relative warmth. This is news because previous work has seen it as more or less a single, protracted period, with maybe some ups and downs," said UNL geologist Christopher Fielding. Fielding is professor of geosciences at UNL and one of the Science paper's UNL co-authors, along with his wife, Tracy Frank, assistant professor of geosciences.

Frank, Fielding and their colleagues found atmospheric CO2 at 280 parts per million in the early portion of their study period and as high as 3,500 parts per million near its end, with many shifts in between. The level of atmospheric CO2 today is about 380 parts per million, the highest it has been in at least 650,000 years. That's nearly half-again as high as it was before the start of the Industrial Revolution in the early 19th century. It's also rising at a faster rate than anything found in the geologic record.

"The rate of change that we may undergo here in the next 100 or 200 years might be a lot faster than we've seen in the past," Fielding said. "We really don't know how the Earth is going to respond to such rapid change . . . That's a level of CO2 (3,500 parts per million) that we've never experienced as human beings, and yet it's been fairly common at times in the past. We're at 380 (parts per million) and people think it's getting warm."

The UNL geologists, Fielding, Frank, doctoral candidate Lauren Birgenheier and postdoctoral researcher Michael Rygel (now at the State University of New York-Potsdam), examined the sedimentary record of glacial activity in eastern Australia, which was at polar latitudes in Paleozoic times.

The rest of the nine-person team, including lead author Isabel Montanez of the University of California, Davis, and UNL alumnus Neil Tabor of Southern Methodist University, looked at changes in late Paleozoic tropical areas. They analyzed the isotopic compositions of soil-formed minerals and fossil plant matter to determine CO2 levels and used fossil shallow-water brachiopods as a proxy, or indicator, for sea-surface temperatures and glacial ice volume. Brachiopods, commonly known as lamp shells, are two-shelled marine animals. The oxygen isotope composition of their shells responds to changes in water temperature and the amount of water stored in ice caps.

Comparison of the data sets collected by the groups indicated CO2 played a major role in forcing climate change during that period.

"The various different records all show coincident trends," Fielding said. "If the evidence for CO2 goes up, so does the apparent sea surface temperature proxy. When that happens, we see our nonglacial record in Australia, and vice versa. When the CO2 levels and the surface temperature go down, we see glacial deposits during those times. All these sets of data were collected independently of each other. That's really the great thing about this paper."

The research was supported by the National Science Foundation.



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