Ice cores suggest current climate is in the natural range of variability
By Summit Voice
FRISCO — Ice cores from West Antarctica spanning the last 2,000 years suggest that recent warming and glacier loss in the region is comparable to other warm periods during that span.
Most of the recent warming may be related to powerful El Niño phases in the tropical Pacific in the 1990s, said University of Washington researcher Eric Steig. The ice core record shows similar temperature spikes in the 1830s and 1940s, he said, adding that the recent warming cannot be attributed with confidence to human-caused global warming.
Steig built on previous research showing that rapid thinning of Antarctic glaciers was accompanied by rapid warming and changes in atmospheric circulation near the coast. The new study suggests that the 1990s were not all that different from some of those earlier warm spells.
“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,” Steig said, summarizing the findings published online April 14 in Nature Geoscience.
The prominent El Niño signal implies that rapid ice loss from Antarctica observed in the last few decades, particularly the 1900s, may not be unprecedented, he said, contrasting the findings in West Antarctica to the Antarctic Peninsula, where rapid ice loss has been even more dramatic and where the changes are almost certainly a result of human-caused warming.
But in the area where the new research was focused, the West Antarctic Ice Sheet, it is more difficult to detect the evidence of human-caused climate change. While changes in recent decades have been unusual and at the “upper bound of normal,” Steig said, they cannot be considered exceptional.
“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?’”
He said what happens to the West Antarctic Ice Sheet in the next few decades will depend greatly on what happens in the tropics.
The work was funded by the National Science Foundation Office of Polar Programs.