Looking Back To Look Forward
May 20, 2013

Ice Age Evidence Sheds Light On Modern-Day Tropical Climate Change Simulations

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redOrbit Staff & Wire Reports - Your Universe Online

Researchers from the University of Hawaii at Manoa and Woods Hole Oceanographic Institution are looking to events of the past to better understand how rainfall patterns across the Indo-Pacific warm pool — the massive pool of warm water stretching along the equator from Africa to the western Pacific Ocean — will change due to global warming.

As part of their study, Pedro DiNezio of the university´s International Pacific Research Center and Jessica Tierney of the Massachusetts-based non-profit organization investigated well-preserved geological clues (also known as proxies) of precipitation patterns during the last ice age.

They then compared those patterns, which come from a time when the Earth was far cooler than it is currently, and compared them with computer model simulations in order to better explain the patterns which they inferred from those proxies. Their records suggested that during the last ice age (26,000 to 19,000 years ago), conditions were drier throughout the center of the Indo-Pacific warm pool.

“For our research, we compared the climate of the ice age with our recent warmer climate. We analyzed about 100 proxy records of rainfall and salinity stretching from the tropical western Pacific to the western Indian Ocean and eastern Africa.” DiNezio, the lead author, said in a statement. “Rainfall and salinity signals recorded in geological sediments can tell us much about past changes in atmospheric circulation over land and the ocean respectively.”

“Our comparisons show that, as many scientists expected, much of the Indo-Pacific warm pool was drier during this glacial period compared with today. But, counter to some theories, several regions, such as the western Pacific and the western Indian Ocean, especially eastern Africa, were wetter,” added Tierney. Their findings were published in Sunday´s edition of the journal Nature Geoscience.

DiNezio and Tierney also compared their findings to a dozen different mathematical climate simulation models, and found that only one reproduced the rainfall patterns suggested by the geological evidence. That model was produced by the Hadley Centre for Climate Prediction and Research in the UK, and the fact that only one in 12 climate models was able to reproduce glacial era rainfall patterns could have widespread implications for simulating tropical climate change, they noted.

“We were taken aback that only one model out of the 12 showed statistical agreement with the proxy-inferred patterns of the rainfall changes. This model, though, agrees well with both the rainfall and salinity indicators — two entirely independent sets of proxy data covering distinct areas of the tropics,” DiNezio said. “The study, moreover, presents a fine benchmark for assessing the ability of climate models to simulate the response of tropical convection to altered land masses and global temperatures.”

“The good news is, the Hadley model combined with the geological evidence show a pathway to improve our ability to simulate and predict tropical rainfall in the future,” added Tierney. “The more we study the mechanisms that governed tropical climate in the past, the better we can predict the climate changes that will affect the billions of people that live in this vast region of the world.”