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Warm summers may have knocked out ice ages


Sydney : Warm summers in the northern and southern hemispheres may have knocked out the ice ages, says a new study.

“It is already known that wobbles in the earth’s orbit drive the ice age cycle but there are several theories as to how they do this,” said study co-author John Hellstrom, University of Melbourne’s School of Earth Sciences.

“The most popular one suggests that ice ages end during a period when the intensity of northern hemisphere summer insolation is greatest,” Hellstrom added.

The results of the new study, which focussed on the end of the penultimate ice age, questions this theory and attributes the variations to the earth’s axial tilt.

Previous research had identified precisely when these orbital “wobbles” occurred, but could accurately date the records of the earth’s response to them, which are found in marine sediment on the ocean floors.

Russell Drysdale from the University of Newcastle’s School of Environmental and Life Sciences (SELS), who led the research with colleagues from Italy, France, Germany and Britain, said ocean sediment cores contain a wealth of information about past global climate.

But beyond about 50,000 years ago it is difficult to determine the exact age of these sediments.

“To overcome this, we studied isotope variations in three stalagmites collected from an Italian cave, and found that these variations relate to ocean temperature changes recorded in sediment cores from the nearby sea floor,” Drysdale said.

“Stalagmites from limestone caves can be very precisely dated using trace amounts of uranium incorporated within their structure,” Drysdale said.

“We applied the accurate time scale of the stalagmite record to the sea floor sediment data. A key property of sea-floor sediments is that they detect the growth and decay of ice sheets.”

“So we have effectively provided an accurate time scale for the collapse of the ice sheets that ended the penultimate ice age. This collapse started around 141,000 years ago,” he added.

“This is as much as 8,000 years earlier than previously thought — too early to be caused by stronger northern hemisphere summers alone, which is the prevailing theory.”

The study was published in the journal Science.