An international team of glaciologists, led by Ohio State University, has discovered new and compelling evidence that the Italian Alps are warming at an unprecedented rate.
The discovery, described at the annual autumn meeting of the American Geophysical Union this past week, was made less than 20 miles from the site where melting ice exposed the 5,000-year-old body of Ötzi the Iceman.
A single, dried-out leaf from a larch tree that grew thousands of years ago provides part of the evidence.
The research team drilled a set of ice cores from atop Mt. Ortles in Northern Italy. Although it has not shown signs of melting for thousands of years, the Alto dell’Ortles glacier now appears to be shifting away from a constantly below-freezing state to one where its upper layers are at the melting point throughout the year.
“Our first results indicate that the current atmospheric warming at high elevation in the Alps is outside the normal cold range held for millennia,” said project leader Paolo Gabrielli, research scientist at Byrd Polar Research Center at Ohio State. “This is consistent with the rapid, ongoing shrinking of glaciers at high elevation in this area.”
Drilling the ice cores in 2011, the team discovered that the first 100 feet of the glacier was composed of “firn,” which is a grainy, compacted snow that has partly melted. Below this level, they found nothing but solid and colder ice all the way down to the frozen bedrock.
The researchers say that this suggests that snow accumulated on the mountain and compacted into ice for thousands of years without ever melting. Until, that is, 30 years ago, when each year’s new deposit of snow began melting.
The preserved larch leaf, which was found wedged into the ice well beyond the firn layer, is evidence that the glacier had previously remained unchanged for a very long time. The leaf, identified as belonging to the Larix decidua, or the European larch, was found around 240 feet beneath the surface and encased in solid ice.
Carbon dating has placed the leaf at approximately 2,600 years old, meaning that Ötzi had already been dead for more than two millennia when this particular larch tree grew, though it was not far from his resting place.
“The leaf supports the idea that prehistoric ice is still present at the highest elevations of the region,” Gabrielli said.
Gabrielli and his collaborators are just beginning to chemically analyze the ice cores. This analysis of trace metals and dust sealed in the ice will give a more detailed set of clues to the climatic conditions when the ice was formed.
Ice cores in the European Alps are unique, according to Gabrielli, because the winter and summer layers of ice accumulation are easily identifiable, offering the promise of a high-resolution climate record.
The team finds the question of why temperatures in the Alps are increasing at twice the global rate of particular interest. Alto dell’Ortles, as the highest glacier in the eastern Alps at 2.4 miles above sea level, is located in the heart of Europe — one of the most industrialized and populated areas of the world. The team intends to continue their research by investigating whether soot emitted by human activities in central and southern Europe plays a role — perhaps by darkening the surface of the glacier, absorbing the sun’s heat and melting ice.
“Ortles offers us the unique possibility to closely verify if and how regional environmental changes can interact with climatic changes of global significance,” Gabrielli said.