THE ASSOCIATED PRESS
"Researcher Finds Ancient Heat Wave "
Thursday, August 13, 1998; 7:36 p.m. EDT
WASHINGTON (AP) -- A heat wave suddenly moved across Africa some 2,000 years ago and lasted for centuries before relenting, according to a study of ancient sediments dredged from the bottom of a mountain lake in Kenya.
Weizmann Institute researchers who did the study said their findings show the global climate naturally goes through cycles of warming and cooling. A current warming trend has been blamed on greenhouse gasses dumped into the atmosphere by industry and transportation.
"Our findings show that the climate can warm up suddenly without any connection to human activity," said Aldo Shemesh, head of environmental sciences at the Weizmann Institute in Rehovot, Israel.
A report on the study will be published Friday in the journal Science. Shemesh said that documenting ancient, natural climate changes will help modern science more accurately determine the manmade effects on the future climate.
He and his colleagues gathered sediment cores from the bottom of Hausberg Tarn, a small lake 14,000 up the side of Mount Kenya. They used a carbon-14 dating technique to determine that some of the bottom material was more than 3,000 years old.
From the corings, the scientists then extracted fossils of algae that lived during those ancient times. By analyzing the ratio of two isotopes of oxygen, they could determine the temperature of the water when the algae lived.
For instance, oxygen-16 is the most common form of oxygen, but the amount of oxygen-18 in the fossils increases when the water cools and decreases when it warms.
The researchers found that the waters in Hausberg Tarn suddenly warmed about seven degrees F between 350 BC and 450 AD. The warming indicates a fundamental shift in the climate of equatorial East Africa occurred during the period, the scientists said.
A number of studies in different parts of the world have found evidence of sudden warming or cooling trends, but the Hausberg Tarn findings are the first from a high altitude, equatorial location.
© Copyright 1998 The Associated Press