New Temperature Analysis Should Aid Climate-Change Studies

"There's a lot of funding and research going into studying the causes of climate change. One of the key questions is, when we go back tens to hundreds of thousands of years, what regions of the planet are responsible for triggering glacial periods?" said Howard Spero, a UC Davis professor of geology. "One hypothesis argues that changes in high latitudes, near the poles, are responsible. The other camp argues that the tropics is the key player because it is the primary source of moisture and heat to the atmosphere.

"We believe we have the smoking gun: the trace mineral content in the shells of these fossilized planktonic foraminifera, which acts as a geochemical thermometer. And the smoking gun supports the hypothesis that the tropics is a very important control on global climate change." Spero is co-author of the study with geology professor David Lea and research geologist Dorothy Pak of UC Santa Barbara. It will be published in Friday's issue of the journal Science.

The study is the first to document very warm sea surface temperatures in the western Pacific about 400,000 years ago, which geologists call marine isotope stage 11 (MIS 11). Spero said the fossil shells show that average surface water temperatures at that time reached 30 degrees Celsius (about 86 degrees Fahrenheit), then moderated.

"It's very intriguing that historical temperatures in the western tropical Pacific have been around 29 degrees Celsius, but have been reaching as much as 30 degrees during the hottest times of the year in the past decade," Spero said.

"Many researchers are studying MIS 11 as a potential analog for future warming. Some researchers have suggested that during MIS 11, melting of the polar ice caps may have raised global sea level by as much as 65 feet. Our results should allow numerical modelers to better explain the geological data and produce more confident predictions of the future."