Archive for the ‘Ice and snow’ Category

The Arctic death spiral

October 1, 2011 Leave a comment

Those following the observations of Arctic sea ice extent and volume were probably not surprised when the summer minimum numbers rolled in and 2011 had the lowest or second-lowest sea ice extent since monitoring began in the 1970’s. The downward trend shows no sign of stopping, and the distinction between lowest or second-lowest is unimportant, as year-to-year extent is influenced by surface wind patterns. No, what is important is this graph from the National Snow and Ice Data Center:


Sea ice extent from the NSIDC


The greyed-region is +/-2 standard deviations, with the central line the 21-year average for 1979-2000. The current extent values, especially at the summer minimum, are strikingly low. Just eye-balling the chart suggests that 2007 and 2011 are approach a deviation of more than 3-sigma from the average. The other years in the past decade are almost as low. What about the volume of sea ice in the Arctic?


Sea ice volume from PIOMASS

While the summer minimum sea ice extent has approximately halved, volume has decreased by almost 75%. This is especially troubling – thin ice responds more rapidly to variations in temperature and weather patterns, and the volume of multi-year ice is in rapid decline.

But sea ice is not the only victim in the Arctic. Last week The Conversation posted a stunning article, “Canadian ice shelves halve in six years”. From the article:

Half of Canada’s ancient ice shelves have disappeared in the last six years, researchers have said, with new data showing significant portions melted in the last year alone.

“Since the end of July, pieces equaling one and a half times the size of Manhattan Island have broken off,” said Luke Copland, researcher in the Department of Geography at the University of Ottawa.

These are shelves that have existed since long-before Europeans arrived. Let that sink in.

From a related article from ABC News:

Between 1906 and 1982, there has been a 90 percent reduction in the areal extent of ice shelves along the entire coastline, according to data published by W.F. Vincent at Quebec’s Laval University. The former extensive “Ellesmere Island Ice Sheet” was reduced to six smaller, separate ice shelves: Serson, Petersen, Milne, Ayles, Ward Hunt and Markham. In 2005, the Ayles Ice Shelf whittled almost completely away, as did the Markham Ice Shelf in 2008 and the Serson this year.

Ice shelves are massive, floating platforms of ice, often at the terminus of marine glaciers. Unlike sea ice, which thins and thickens with the seasons and is constantly jostled around by winds, these shelves are more permanent, though still dynamic, features. They are only native to the Arctic regions, as the ice would otherwise melt long before it reached the sea if annual-average temperatures were not sub-freezing. The primary mechanism for ice loss from these shelves is calving – when the ice reaches a certain distance beyond the grounding line, where it is anchored to the seabed, chunks mechanically shear off to form icebergs.

However, ice shelves across the world have been losing mass over the past decades, many at an ever-accelerating pace, including the dramatic collapse of the Larsen Ice Shelf in Antarctica. Glaciologists have pinpointed two major sources for this acceleration – warming ocean waters that undermine the shelf from below, and surface melt-water pools that chisel vertical fractures into the shelf, greatly reducing its structural integrity.

The accelerating decline of sea ice, ice shelves, and glaciers is but one line of evidence that demonstrates the world is warming. Unfortunately, the loss of ice contributes to the ice-albedo feedback and is set to not only disrupt ecosystems, but threaten water supplies for the millions that rely on glacial meltwater. Perhaps, though, the visibility of this phenomenon will finally start to resonate in people.

The great retreat of Jakobshaevn Isbrae in Greenland, via GRID-Arendal

We live in a changing world – we clearly have the power to disrupt it for the worse, but that also means we have the ability to shape it for the better.

Categories: Arctic, Ice and snow