From ENN : Since the dawn of time, Earth has constantly cycled through ice ages and warming periods due to its unsteady orbit about the sun. Previous studies believed the warming of the northern hemisphere was the sole trigger for the start of the deglaciation of the southern hemisphere during the last ice age about 18,000 years ago. Recent findings, however, show Antarctica started to warm 2,000 to 4,000 years before this.
Previous evidence about Antarctic climate change has come from ice cores drilled in East Antarctica, the highest and coldest part of the continent. However, a US-led research team studying a new ice core from West Antarctica found that warming there was well under way 20,000. The findings come from a detailed examination of an ice core taken from the West Antarctic Ice Sheet Divide, an area where there is little horizontal flow of ice.
The ice core is more than 2 miles deep and covers 68,000 years, though so far data have been analyzed only from layers going back 30,000 years. Near the surface, 1 meter of ice covers one year, but at greater depths the annual layers are compressed to centimeters.
T.J. Fudge, a University of Washington doctoral student in Earth and space sciences and lead corresponding author of the Nature paper, identified the annual layers by running two electrodes along the ice core to measure higher electrical conductivity associated with each summer season. Evidence of greater warming turned up in layers associated with 18,000 to 22,000 years ago, the beginning of the last deglaciation.
“Sometimes we think of Antarctica as this passive continent waiting for other things to act on it. But here it is showing changes before it ‘knows’ what the north is doing,” said Fudge.
He noted that the warming in West Antarctica 20,000 years ago is not explained by a change in the sun’s intensity. Instead, how the sun’s energy was distributed over the region was a much bigger factor. It not only warmed the ice sheet but also warmed the Southern Ocean that surrounds Antarctica, particularly during summer months when more sea ice melting could take place.
Today, however, the Earth’s orbit is not the most influential factor regarding climate change. Carbon dioxide emissions play one of the largest roles in today’s rapidly changing climate.