April 15, 2013
Antarctic Glacial Melt Part Of A Natural Cycle, Says New Study
Brett Smith for redOrbit.com - Your Universe Online
As the debate over climate change continues, so does the publication of studies that support or challenge the notion that human activity is the main driver of rising temperatures.
According to a new study in“¯Nature Geoscience, the dramatic thinning of glaciers in Western Antarctica is due to natural variation, and cannot be attributed directly to carbon emissions.
"If we could look back at this region of Antarctica in the 1940s and 1830s, we would find that the regional climate would look a lot like it does today, and I think we also would find the glaciers retreating much as they are today," said the study´s lead author“¯Eric Steig, a professor of Earth and space sciences at the University of Washington.
The scientists noted that the largest recent period of Antarctic warming occurred during the 1990s as the result of a particularly lengthy and strong set of El NiÃ±o conditions in the equatorial Pacific Ocean. Many other decades, including pre-industrial times such as the 1830s, also showed marked temperature spikes, according to the latest report.
The team based much of their study on the analysis of a new series of ice cores from the West Antarctic Ice Sheet Divide. The ice cores represent a cross-section of ice that has accumulated over the past 2,000 years. The researchers also culled data from scientific ice core records dating back about 200 years.
An analysis of the ice cores showed elevated levels of the oxygen-18 to oxygen-16 isotope ratio, which typically indicate warmer air temperatures. The isotope ratios showed that the 1990s had the warmest temperatures over the last 200 years, but were comparable to levels reached during other decades, such as the 1830s and 1940s.
According to Steig, this evidence suggests that the receding glacier pattern in this region of Antarctica, which he called the "upper bound of normal,” could be part of a very natural and cyclical pattern.
"The magnitude of unforced natural variability is very big in this area," Steig said, "and that actually prevents us from answering the questions, 'Is what we have been observing exceptional? Is this going to continue?'”
Stieg added that the fate of the West Antarctic Ice Sheet over the coming decades will depend largely on the activity of El NiÃ±o and other tropical forces.
While the receding glaciers in Western Antarctica may be part of a natural cycle, other studies have shown that the same is not true for other sections of the continent. Another study published in Nature Geosciences this week showed that the part of the continent closest to South America known as the Antarctic Peninsula is experiencing the fastest rate of glacial melt in the past 1,000 years.
According to the scientists who studied the peninsula, this rapid ice loss destabilizes the surrounding ice shelves that extend out from the continent and into the Southern Ocean. These ice shelves act as buffers for the interior ice sheets. If the buffers disappear, the region's glacial melt could speed up and potentially result in a destructive rise in sea level.