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Arctic summer ice cover is 31st highest ever recorded

Oh, and the Northeast Passage is open as normal

It's that time of year when the sea ice in the Arctic shrinks to its annual minimum, and it appears that this year's figure is most probably in. It's the 31st largest minimum extent on record, as it happens, which isn't especially newsworthy as reliable records only go back 35 years.

It's a lot more fashionable to report this as the fourth lowest on record, and not to mention how short that record is. But the fact is that in a set of only 35 results, even an actual lowest or highest value wouldn't be a big deal. Fourth lowest is of no real significance at all.

Nonetheless, there are at least two US government press releases heralding the latest figure as a harbinger of doom, from the US National Snow and Ice Data Center and NASA. The NSIDC, indeed, goes on to tell us:

Both the Northern Sea Route, along the coast of Russia, and Roald Amundsen’s route through the Northwest Passage are open ... The deeper and wider Northwest Passage route through Parry Channel, which consists of M’Clure Strait, Barrow Strait, and Lancaster Sound, still has some ice in it.

Amundsen made his sea voyage through the Canadian Arctic in 1903-6; nobody knows what the summer minimum ice reach was like back then because we didn't have satellites, but presumably the NSIDC's information is relevant in some way. Maybe the ice was retreating as much in those summers as it has done this year?

There still weren't any ice-scanner satellites during the summer minimum of 1969, when the 100,000-ton supertanker Manhattan - at the time the largest merchant vessel on the US registry - transited the Northwest Passage. The M'Clure strait was blocked then, too, just as it is this year, but the Manhattan got through via a route south of Banks Island. It sounds as though ice conditions that summer may not have been too dissimilar to this year.

As for the eastern route north of Siberia, a lot of people think that has only been passable in recent years. But it's not true.

None of those historical facts proves anything in particular about this year's ice minimum: they do, however, bring a bit of context to the NSIDC's suggestion that there is something unusual about the northern sea routes being open just now.

Some more context on the fourth-lowest-on-record ice figure might also be provided by recent research showing that the arctic ice cap has staged a remarkable recovery in recent years. It would also be possible to point out that while the north pole has seen generally lower sea ice area earlier in the past decade, the south pole has seen significant increases - indeed, the most recent annual maximum down south was an all-time record high (not fourth highest).

As a result, total world sea ice extent has been above the average of the satellite record for most of the last three years.

And finally, it's perhaps worth noting that the UK Met Office, among others, suspects that the Atlantic Multidecadal Oscillation (AMO) mechanism is about to flip into a cold phase. The AMO has been warming the northern Atlantic up since the mid-'90s, and the north Atlantic is the ocean most open to the Arctic. (Perhaps coincidentally, it was in the mid-'90s that the arctic ice started its recent spell of shrinkage.)

If the AMO does turn cold, it's at least possible that the arctic ice recovery seen over the last couple of years will continue. Whether it does or doesn't, vessels will still transit the ice region occasionally, to the no doubt perpetual amazement of the world's media. ®

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