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More sea ice from global warming?

Mar 23, 2009

To the editor: In an apparent paradox presented by global warming, higher temperatures can, in fact, result in heavier seasonal sea ice near shore. This phenomenon is the result of increased snowfall as a consequence of the presence of warmer air laden with the abundant moisture available from the nearby sea. Accretion of snow makes the coastal glaciers more active, depositing additional ice and snow into the sea. The result is a decrease in salinity, as well as localized cooling of the sea water, allowing it to freeze even at a somewhat warmer temperature.

During our four voyages in the Labrador Sea aboard our 44-foot steel ketch, Tamara, we observed an increase in the number and size of icebergs carried by the southward-flowing Labrador Current, down Iceberg Alley toward the Grand Banks, and thence into the Atlantic to meet the Gulf Stream. Of great concern to scientists, particularly because of potential changes to the Gulf Stream, is the decrease of both salinity and ambient water temperature that results from this increase in ice literally pushed into the sea by increased snowfall on coastal Greenland.

The driving force of major ocean currents, both in the northern and southern hemispheres, is the interrelationship between salinity and water temperature, known as thermohaline circulation. Even relatively small changes in this balance could result in dramatic climate shifts.

Satellite measurements since 1978 have revealed that the surface area covered by single season sea ice off Antarctica has increased by an average of 0.5 percent annually. But it is a matter of scientific debate as to whether near shore seasonal sea ice covers as much territory as the early 1970s.

A 2005 NASA study confirmed that increased global temperatures have in fact caused more snowfall around the continent of Antarctica. The very weight of this snow is pushing sheets of ice seaward, in turn cooling the near shore water and decreasing its salinity, allowing it to more readily freeze over. Further from the coast, however, glaciers may be retreating.

Not to be confused with the detachment of massive Antarctic ice shelves, or with the decrease of approximately 3 percent per decade of surface area of sea ice in regions of the Arctic remote from costal glaciers, the increase in single season sea ice off Antarctica, is considered an indicator of increasing global temperature.

Notwithstanding this incremental increase in Antarctic coastal sea ice, most anchorages suitable for use by small craft are generally open during the prime voyaging months of January and February. National Oceanic and Atmospheric Administration ice charts are available online at www.natice.noaa.gov.

—Mark Roye and Nancy Krill sail aboard their 44-foot Swedish-built steel ketch Tamara. They have made numeous passages to Labrador, and recently sailed to Antarctica.

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