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Temperature rise in central China over last 20,000 years greater than previously thought: U.S. study

English.news.cn   2013-05-15 10:36:27            

LOS ANGELES, May 14 (Xinhua) -- New data reveal that the temperature has risen 10 to 14 degrees Fahrenheit (6 to 8 degrees Celsius) in the last 20,000 years in central China, with the increase two to four times greater than what many scientists previously thought.

"Before our study we did not have data that could tell us whether those changes were small or large," said Robert Eagle, lead author of the research published in the early online edition of the journal Proceedings of the National Academy of Sciences.

The research, which for the first time accurately determines temperature on land at the time of the last ice age, is beneficial to scientists interested in understanding climate change, as well as geology, Eagle, who works in the Department of Earth and Space Sciences at UCLA, told Xinhua in an email.

The technique applied in this study, clumped isotope thermometry, is the most accurate land-based temperature determination tool available today.

It measures subtle atomic differences in the compound calcium carbonate and allowed scientists to say with more confidence how temperatures have warmed in central China, and how the chemistry of rainfall has changed.

"We can calculate temperatures and reconstruct the chemistry of rainwater from the past ice age, then compare this to the present day climate in specific regions. We can then use this information to validate current climate models and study atmospheric processes," Eagle said.

The study was conducted in central China on the Loess Plateau, a vast agricultural region of 647,500 square km that is home to more than 50 million people.

Researchers collected two unique sample types, land snail shells and soil deposits, from the Loess Plateau region. While snails calcify quickly over just a few years, soil carbonates grow over longer time periods ranging from a few hundred to thousands of years.

This area is renowned for its wide expanses of wind-blown dust deposits, or loess. As dust and soil builds up on the loess plateau, it preserves signals of the climate at the time it was deposited, and this makes it a very valuable archive of past climates.

"We were drawn to study them because they preserve an exceptional record of climate change in this very important agricultural region", Eagle said, "the East Asian monsoon is one of Earth's most significant climate phenomena and understanding its sensitivity to climate forcing is crucial, as is our ability to capture and predict its response with climate models."

"One of the most important aspects of the study was showing that we could get the same result from such different types of carbonates, even though these materials integrate over very different time frames, they gave us the same result," said Aradhna Tripati, UCLA assistant professor in the Departments of Earth and Space Sciences.

Climate models that are used for predicting future climate change all show evidence for global warming in response to rising greenhouse gas levels over the next 50 to 100 years. Some models predict a small amount of warming will occur in this time frame, and others predict a large amount of warming. They also show large differences in how rainfall will change in the future.

"One of the reasons we studied changes over the last 20,000 years in central China was to find out why some models are able to simulate how climate has changed in a specific region," Eagle said.

Similar types of sediments exist in the U.S. Midwest, from Mississippi to Nebraska, and are currently being studied by the scientists.

Editor: Lu Hui
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