April 23, 2013
Ancient Climate Shift Highlights Link Between Greenhouse Gases And Terrestrial Temperature
Brett Smith for redOrbit.com - Your Universe Online
A new technique has allowed a team of British and American scientists to connect temperatures to a massive shift in atmospheric carbon dioxide that occurred around 34 million years ago, according to a new study in the Proceedings of the National Academy of Sciences.Scientists have described this transformation in global climate as a shift from a warm, high-carbon dioxide "greenhouse" condition to a temperate, low-carbon dioxide state of the modern "icehouse" world. As the transformation took place, continental ice sheets spread across Antarctica, scores of animal groups changed habitats, and oceanic temperatures dropped.
In the study, the scientists describe how a groundbreaking technique allowed them to determine that temperatures plummeted by as much as 18 degrees Fahrenheit for fresh water during the warmer months and 10 degrees for the atmosphere in the North Atlantic.
"One of the key principles of geology is that the past is the key to the present: records of past climate inform us of how the Earth system functions," said lead author Michael Hren, Assistant Professor of Chemistry and Geosciences at the University of Connecticut.
"By understanding past climate transitions, we can better understand the present and predict impacts for the future."
Current theories surrounding this massive shift in global temperatures during the Late Eocene and the Oligocene epochs“¯are supported by information gathered from geologic cores drilled deep in the oceans. However, Hren and his colleagues used a newly developed tool known as ℠clumped isotope thermometer´ to scan terrestrial fossil shells from this same time period.
Using fossilized snails collected from the Isle of Wight in Great Britain, the team performed an isotope analysis that allowed them to examine not only the number and ratio of carbon and oxygen isotopes, but also how they were chemically bonded together. Because these bonds are temperature-dependent, they can serve as a reliable indicator of the terrestrial climate in which they were formed.
"While our understanding of past changes in the temperature of Earth's oceans is well established, deciphering the environmental conditions of terrestrial settings has remained elusive," said Kyger Lohmann, director of the Stable Isotope Laboratory at the University of Michigan.
"The application of the clumped-isotope technique provides a unique record of temperature change on land where earlier estimates based on other proxies were either imprecise or ambiguous," he added. "This illuminates the response of the terrestrial climate system during this interval of declining carbon dioxide."
Previous studies have shown that before global temperatures dropped, Earth's atmosphere contained 1,000 parts per million (ppm) of carbon dioxide“¯or more. By the end of the shift, it was thought to be less than 600 ppm.
Hren warns that current trends put Earth on the path to nearly 1,000 ppm in the next 100 years. If that prediction comes true, the Earth could experience the Eocene shift in reverse, toward a much warmer climate that could dramatically impact sea levels and animal migrations.
"The terrestrial setting is the habitat of humanity," Lohmann said. "Therefore, understanding the magnitude and heterogeneity of temperature change on land is essential if we are to model and predict the future impacts on society as our climate warms."