May 20, 2004

Boise State Researchers Study Causes of Climate Change in Nature Article Published Today

A study co-authored by researchers at Boise State University and published today in the leading scientific journal Nature offers new insights on how climate change occurs, including the previously unrecognized role tropical and subtropical regions may play in the process.   Mitch Lyle and Annette Olivarez Lyle of the Center for Geophysical Investigation of the Shallow Subsurface at Boise State collaborated with lead researcher Christina Ravelo of the University of California-Santa Cruz and other scientists on a  study of climate conditions that existed 5 million to 1.8 million years ago. During the warm Pliocene epoch that began about 5 million years ago, sea levels were 50 to 60 feet higher and the Hagerman horse likely grazed on grasslands that covered southern Idaho. But conditions changed about 1.8 million years ago during the Pleistocene period as polar ice sheets covered more of the Northern Hemisphere and the climate cooled, Lyle said. Ravelo and the Boise State researchers identify a gradual global cooling caused by multiple events, including the uplift of mountains and the separation of oceans, that led to the ice ages. Paradoxically, the cooling was caused more strongly by changes in warm tropical oceans, not in polar regions.  The results of this study are particularly important because they contradict a widely held hypothesis that the ice ages were triggered by a single threshold event and the rest of the cooling was directly linked to climate feedback from the development of the Arctic ice cap.    The study also concluded that the Earth’s climate system is much more sensitive to environmental changes and  fluctuations than it was in the distant past — insights that have relevance for current concerns about global warming, according to Lyle. “During a sensitive period for climate such as the Earth is now experiencing, human-induced changes might have had more effect than they would have had if they had occurred 3 million years ago,”  Lyle said. The exact reasons for the climate shift to the cooler Pleistocene period are unknown, but by looking at a time scale of millions of years, researchers can detect clues that are invisible over a shorter time period. For example, the researchers discovered that tropical and subtropical regions experienced only small fluctuations in temperature during the transition from the Pliocene to Pleistocene, while at the same time northern latitudes experienced a much larger temperature change. “Even though the tropics and subtropics seem like a very stable part of the climate system, these small changes were significant,” said Lyle. The study published today in Nature was based on data obtained from sediment cores obtained from the bottom of the Pacific Ocean. Lyle and other scientists obtained the cores in 1996  during an expedition to the Pacific Ocean as part of the Ocean Drilling Program funded by the U.S. National Science Foundation. Lyle has participated in about 30 such oceanographic expeditions, and is planning an expedition to the South Pacific to survey drill sites in the next few years. Samples from the sediment cores were later sent to Boise State’s geosciences department, where geology master’s student Suzy Shaub, under the direction Olivarez Lyle, analyzed more than 1,200 samples to characterize the organic carbon and carbonate concentrations in the sediment layers. The layers can be used to calibrate “yardsticks” for measuring geologic time. “The sediment cores we used are archived in a sediment ‘ library’ so that other researchers have the opportunity to do further studies to compare with our data,” Lyle said. According to Lyle and Olivarez Lyle, the study published in Nature offers some intriguing information that may help lay the groundwork for further research endeavors. “The paleoclimate is more than history. It’s an opportunity to look at the processes beyond the human time scale,” Lyle added. “It’s intrinsically fascinating, and it also helps us understand how the climate continues to change today.” -end- Contact Mitch Lyle CGISS 426-1167 mlyle@boisestate.edu Annette Olivarez Lyle CGISS 426-3004 alyle@boisestate.edu Media contact Janelle Brown communications and marketing 426-1790 jbrown2@boisestate.edu