Today's climate more sensitive to carbon dioxide than in past 12million years - Laser Tattoo Remova

The research shows that, in the last five million years, changes inocean circulation allowed Earth's climate to become more closelycoupled to changes in carbon dioxide concentrations in theatmosphere. The findings also demonstrate that the climate of modern times morereadily responds to changing carbon dioxide levels than it hasduring the past 12 million years. "This work represents an important advance in understanding howEarth's past climate may be used to predict future climate trends,"says Jamie Allan, program director in the National ScienceFoundation's (NSF) Division of Ocean Sciences, which funded theresearch. The research team, led by Jonathan LaRiviere and Christina Raveloof the University of California at Santa Cruz (UCSC), generated thefirst continuous reconstructions of open-ocean Pacific temperaturesduring the late Miocene epoch.

It was a time of nearly ice-free conditions in the NorthernHemisphere and warmer-than-modern conditions across the continents. The research relies on evidence of ancient climate preserved inmicroscopic plankton skeletons--called microfossils--that long-agosank to the sea-floor and ultimately were buried beneath it insediments. Samples of those sediments were recently brought to the surface incores drilled into the ocean bottom. The cores were retrieved bymarine scientists working aboard the drillship JOIDES Resolution. The microfossils, the scientists discovered, contain clues to atime when Earth's climate system functioned much differently thanit does today.

"It's a surprising finding, given our understanding that climateand carbon dioxide are strongly coupled to each other," LaRivieresays. "In the late Miocene, there must have been some other way for theworld to be warm. One possibility is that large-scale patterns inocean circulation, determined by the very different shape of theocean basins at the time, allowed warm temperatures to persistdespite low levels of carbon dioxide." The Pacific Ocean in the late Miocene was very warm, and thethermocline, the boundary that separates warmer surface waters fromcooler underlying waters, was much deeper than in the present. The scientists suggest that this deep thermocline resulted in adistribution of atmospheric water vapor and clouds that could havemaintained the warm global climate. "The results explain the seeming paradox of the warm--but lowgreenhouse gas--world of the Miocene," says Candace Major, programdirector in NSF's Division of Ocean Sciences.

Several major differences in the world's waterways could havecontributed to the deep thermocline and the warm temperatures ofthe late Miocene. For example, the Central American Seaway remained open, theIndonesian Seaway was much wider than it is now, and the BeringStrait was closed. These differences in the boundaries of the world's largest ocean,the Pacific, would have resulted in very different circulationpatterns than those observed today. By the onset of the Pliocene epoch, about five million years ago,the waterways and continents of the world had shifted into roughlythe positions they occupy now. That also coincides with a drop in average global temperatures, ashoaling of the thermocline, and the appearance of large ice sheetsin the Northern Hemisphere--in short, the climate humans have knownthroughout recorded history.

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