Newspaper article The Christian Science Monitor

Unlocking Secrets of the Ice

Newspaper article The Christian Science Monitor

Unlocking Secrets of the Ice

Article excerpt

John Overpeck's job is like putting together a huge, complicated jigsaw puzzle. He may find one piece on the bottom of an African lake and another one deep in an Arctic glacier. The puzzle he's working on is a picture of what the Earth's climate was like thousands of years ago. Dr. Overpeck is a paleoclimatologist (PAY- lee-oh-kly-muh-tohl-uh-jist). "Paleo" means "ancient" in Greek. He studies ancient climates.

Why do scientists want to know what the weather was like 1,000 years ago? Weather patterns have a big impact on people. They determine where we live and how our food grows. Scientific measurements suggest that the average temperature of Earth's atmosphere has risen by 0.5 degrees Centigrade (0.9 degrees Fahrenheit) since 1860. That's a tiny but significant amount. Most scientists now think that human activity has contributed to "global warming." But they can't say for sure until they know what ancient weather patterns were like and how they changed.

That's where Overpeck comes in. He's the director of the Institute for the Study of Planet Earth at the University of Arizona at Tucson.

"Climate" and "weather" are different. Weather changes quickly. Thunderstorms come and go, heat waves break, cloudy days clear up. Climate is the "normal" weather we expect over a longer period of time - inches of precipitation per month, average summer temperature for the past 10 years, number of floods per century.

Weather records date back only 140 years in this country. So, how can scientists find out what Earth's climate was like in the days before thermometers, rain gauges, barometers, and anemometers (wind- speed indicators)?

Paleoclimatologists look at substitute, or "proxy" records. These records include the width of growth rings in trees, how thick the layers are in an ice-core sample, the composition of coral, the presence of pollen grains, the thickness of the sediment layers in ocean and lake beds, even old historical records.

"None of the proxies is perfect," Overpeck says. "That's why we want multiple records, so that we can compare them and look for common signals."

Overpeck might look at samples from a lake bed in Ghana. He knows that the width of the bands of sediment that accumulate each year depends on how much dust blows into the lake. Dry years mean more dust and thicker layers. Wet years produce thinner layers. He might also look at the pollen preserved in the samples, to find out what plants were growing in the area. Plants are clues to climate.

Diaries, farmers' planting records, and newspaper accounts might also contain hints about the weather. The writers may not know what the temperature was. But by knowing when crops were planted or harvested, or if the year was wet or dry, scientists can make assumptions about the climate. …

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