- WASHINGTON (AP) -- Providing evidence of cycles of global warming and cooling
that have nothing to do with man's actions, researchers studying ancient
sediments dredged from the bottom of a mountain lake in Kenya have found
that a heat wave suddenly moved across Africa 2,000 years ago and lasted
for centuries before relenting.
- Weizman Institute researchers who did
the study said their findings show the global climate naturally goes through
natural cycles of warming and cooling. A current warming trend has been
blamed on greenhouse gasses dumped into the atmosphere by industry and
- "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 Weizman Institute in
- 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