Study hints at extreme climate change

October 28, 1999

Web posted at: 1:07 p.m. EDT (1707 GMT)

By Environmental News Network staff

Abrupt climate change could be in the future for the Earth if a recently discovered pattern repeats itself. After analyzing sediment from the subtropical Atlantic Ocean deposited during the last ice age, scientists discovered extreme temperature fluctuations occurred during and at the end of the period.

The scientists found that even during an ice age, warm oceans can heat up.

"What is new here is clear evidence that the warm Atlantic, like the polar Atlantic, was undergoing very large and very rapid temperature changes during the last glacial period," said Scott Lehman, a research associate at the University of Colorado Institute of Arctic and Alpine Research.

Discovering changes in the warm Atlantic is important because warm oceans increase the temperature of the Earth. The vast surface area of Earth's warm oceans creates much more water vapor than cold oceans, increasing atmospheric heat trapping.

"The temperature of the warm ocean realm regulates the water vapor content of the atmosphere and its greenhouse capacity," said Lehman. Past temperature records and climate models suggest ocean circulation changes, like those in the last glacial period, can be triggered by human activity, showing that "the impact of possible future circulation changes may be more dramatic and widespread than suspected," he said.

Lehman and Julian Sachs, a former CU-Boulder researcher at INSTAAR now at Columbia University's Barnard College wrote a paper on the study that appeared in the Oct. 22 issue of Science.

Lehman and Sachs' study revealed temperature changes in the Sargasso Sea between the West Indies and the Azores fluctuated repeatedly by up to 9 degrees Fahrenheit from 60,000 to 30,000 years ago. The last ice age happened between 110,000 and 10,000 years ago, said Lehman.

"The records reveal a large, two to five degrees Celsius temperature change in the subtropical Atlantic Ocean," said Lehman. "That's comparable to the total change between the ice age and the present day at the same location."

Lehman and Sachs reached their conclusions after studying 50 meters of sediment cores hauled up from several miles deep in the Sargasso Sea near Bermuda by French scientists as part of an international project. They analyzed the saturation state of organic molecules from planktonic algae over the past 100,000 years, revealing sea-surface temperatures during that period.

"The warming at the end of the last ice age, about 10,000 years ago, was supported by the disappearance of enormous ice sheets, a one-third increase in atmospheric carbon dioxide levels and changes in the seasonal distribution of the sun's energy," said Lehman. "But the abrupt changes we documented during the last ice age seem to be almost entirely ocean driven."

Melting glaciers send fresh water into the Earth's oceans and scientists believe this cycle triggers abrupt and long-lasting cooling events, including ice ages, by interfering with the conveyor belt of water carrying heat from the tropics to temperate regions. "Numerical modeling studies show that similar changes can be triggered by warming associated with human emissions as well," said Lehman.

"Trapping more heat in the atmosphere has the potential to kill major parts of ocean circulation, with the effects reverberating throughout the world," he said.

The scientists next hope to determine if similar changes occurred in the much larger Pacific Ocean, said Lehman. "If so, any human-induced changes to the ocean's plumbing are likely to affect everyone on Earth, not just Greenlanders and northern Europeans."

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