Deciphering the Coral Code

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POLYP DICTION Like cross-sections of old trees, cores taken from old corals reflect the climatic changes that accompanied their growth. On Australia's Great Barrier Reef, chemical studies of coral columns up to 8 m tall are yielding weather records that go back almost 500 years.

The story they tell is surprising, says Erica Hendy, a researcher at the Australian National University's School of Earth Sciences. In the 18th and 19th centuries, while Europe and North America were shivering their way to the end of a 400-year-long Little Ice Age, the tropical Pacific was as warm as in the 1980s.

In most climate records, says Hendy, "the 20th century stands out as being much warmer than earlier periods." But those records tend to be from the northern hemisphere, she says. "We're suggesting it doesn't look that way everywhere. While there was an ice age in some regions, in the tropics something else was happening."

The coral record also shows that the west Pacific was saltier in the Little Ice Age than it is today. Hendy speculates that water vapor sucked from the tropics helped keep Europe cold: propelled toward the poles, it became snow that fed the era's vast glaciers. When the glaciers melted, the tropical oceans freshened fast.

"It's exciting to see how the climate changed before any possible human influence," Hendy says. And reassuring that well before the arrival of measurement-mad Europeans, tiny coral polyps were keeping such meticulous weather records.

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