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Yet another ice island

On or shortly before 5 August 2010, a big chunk of the floating tongue of Petermann Glacier in northwest Greenland broke off. It is now an ice island, about 260 km2 in area, and is destined to do a left turn into Nares Strait, between Greenland and Ellesmere Island, whence it will drift southwards, falling to pieces as it goes. The new ice island joins a quite long list of old ice islands.

The calving event had been expected for at least a couple of years, based on observations of the floating tongue of the glacier. The island itself seems to have been noticed first by Trudy Wohlleben of the Canadian Ice Service, which scrutinizes satellite imagery continuously for the monitoring of hazards to navigation in northern waters.

These days, big environmental events invite speculation that they are “caused” by global warming. Thus a large new iceberg has to be a sign that either its parent glacier is disintegrating or the global-warming alarmists are at it again. The truth, as usual, is that we cannot put any single event down to global warming in this simple-minded fashion. (Which doesn’t mean, by the way, either that the glacier isn’t disintegrating or that we alarmists are not at it again.)

Some ice shelves in the Antarctic have disintegrated spectacularly in the past couple of decades, and there we do suspect a link with global warming. But the calving of icebergs is a normal part of the mass balance of any tidewater glacier, and once in a while we get a berg that, like the new Petermann berg, is big enough to qualify as an ice island. To show that the balance has shifted to faster calving is very difficult because the big events happen so infrequently.

That doesn’t mean that the new ice island isn’t interesting, and especially not that it isn’t dangerous. The Canadian Ice Service will no doubt eventually produce a story about this one at least as interesting as the one about the last big berg from Petermann. It calved in July 2008, and bits of it remained identifiable near the southern tip of Baffin Island a year later.

But as ice islands go, even the much bigger Petermann island of 2010 is not that big a deal. The first ice island to be given a name — of a sort — was T1. The T stands for “target”. T1 was discovered by U.S. Air Force pilots flying out of Barrow, Alaska, in August 1946. By that date it was clear that the tense wartime alliance between the western allies and the Soviet Union had fallen apart. T1 immediately became a military secret, but it took only a few years for the U.S. military to work out that it is a bit silly trying to keep a 700 km2 chunk of ice secret. T1 was followed by T2, of more than 1000 km2; by T3, of about 50 km2; and eventually by several dozen smaller islands, all of them bigger than your typical iceberg.

Most were in the Arctic Ocean. Each of the biggest ones was spotted from time to time, and found to be drifting in about the expected direction, that is, clockwise, around the Beaufort Sea.

Apart from a debatable suggestion that T2 might have been seen at 72°N off east Greenland in 1955, I haven’t managed to find out what happened to either T1 or T2, but T3 became a research station in 1952. It was occupied intermittently until the early 1970s and was last sighted in 1983, after which it is conjectured to have found its way into Fram Strait and thence into the Atlantic.

The odds are heavily in favour of all these objects having broken free from the northern coast of Ellesmere Island, sometime during the 1920s or later. The evidence of the earliest visitors, and the results of more recent field studies, agree that there was once a continuous ice shelf all along that coast. Today, it consists of a dwindling collection of small remnants. According to the Canadian Ice Service, relying on imagery up to 22 August 2010, another 50 km2 fragment has just detached from what is left. This fragmentation over decades is wholly consistent with the emergence of the global climate from the Little Ice Age.

Moira Dunbar, in the paper from which I have distilled this information, presents several accounts from 19th-century explorers which sound persuasively like descriptions of ice islands. So we have a long record of ice islands off the northern coast of North America. What we cannot do, and will probably be unable to do given the small number of calving events, is to establish that the rate of breakoff has increased.


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