Washington, March 3 (ANI): In a new study, German and Russian climate researchers have found that there were at least two short warming periods in the transition between the last interglacial and glacial epochs
, around 115,000 years ago.
Samples less than 10,000 years old had an average temperature of 29.6oC, while older samples, from the glacial epoch
, averaged 24.2oC, the scientists report in the July 21 Science.
Like counting tree rings, scientists can look back through the annual ice layers to trace how temperature, gas concentrations, and other factors varied during the last glacial epoch, which persisted from 115,000 until 10,000 years ago.
But the newer evidence of worldwide temperature shifts has convinced Broecker that the tropical ocean might represent a critical and as-yet-overlooked force of change during the glacial epochs.
Called the Climate Long-Range Investigation and Mapping Program (CLIMAP), this effort found that the mix of plankton species currently living in the tropics closely resembles the community during the last ice age, signaling that minimal temperature change occurred there during the glacial epoch
. In contrast, the variety of species in the midlatitudes changed dramatically, indicating that the surface ocean during the ice age was 4 degrees C to 12 degrees C cooler during summer months than it is now.
For nearly 2 million years, Earth has been moving to the rhythm of the ice ages, bopping back and forth between long glacial epochs
and short, balmy spans known as interglacials.
During glacial epochs
, iron-rich dust blowing off the arid continents could have caused a continual fertilization, thus cooling the world, he explains.
The findings raise concern because scientists had long thought that interglacial spans -- such as the current one -- were immune from the unstable climate swings that characterize glacial epochs
"The notion that glacial epochs
could be due to changes inCO.sub.2 is an old idea," says Walker.