Shipping companies have been forced to change routes across the North Atlantic in response to an unprecedented early swarm of icebergs. Although not yet on the scale of a Heinrich event, usually seen when ice ages end, this year may break records from the time we have been tracking iceberg numbers in the shipping lanes.
On April 7, the North American Ice Service (NAIS) reported 481 icebergs in the area off the east coast of Canada, a record for this time of year. Of these, 455 were in the transatlantic shipping lanes south of the latitude 48º north. An astonishing 65 were packed into an area 1º by 1º.
At this time of year, the average for the entire region is usually 83.
Passenger travel between Europe and North America may have shifted to the air since the days of the Titanic, but plenty of cargo takes a similar route by sea. Radar has helped limit collisions, but dodging floating ice mountains is no way to travel fast. Instead, ships are detouring south, burning more fuel and delaying the arrival of cargo on each side of the Atlantic.
The immediate cause of the outburst appears to have been strong winds in Baffin Bay, off the southwest coast of Greenland, breaking up sea ice early and causing it to drift south with the currents.
However, there is good reason to think global warming created the conditions under which this could occur. Just last week a paper in Nature Communications reported that the Greenland Ice Cap reached a “tipping point” in 1997. Since then winter refreezing has not balanced the melting of ice around the periphery of Greenland. Almost 500 billion tonnes (551 billion tons) of ice has been lost in the last dozen years.
Although Greenland's volume of ice is dwarfed by Antarctica's, it accounts for 43 percent of current sea level rise. Much of this comes from icebergs calving off glaciers along its western coast and melting as they drift to warmer waters. These icebergs don't just pose a danger to shipping, they may be contributing to the weakening of the Gulf Stream, with disastrous implications for the climate of northern Europe.
Icebergs need to be at least 560 square meters (6,000 square feet) to be included in these counts and stick up 5 meters (16 feet) above the water line. The annual average number of icebergs entering the North Atlantic shipping lanes is 479, usually between May and June, with 1984 holding the record at 2,202.
Despite the important implications both for transport and global climate we have limited understanding of what determines iceberg numbers in the shipping lanes. The US Coast Guard believes variations in the North Atlantic Oscillation (NAO) play at least as much a part of it as the numbers of icebergs produced in Greenland, with recent positive NAO conditions blowing ice offshore.
[H/T: Robert Scribbler]