Top ten weather stories for 2009: story six
6. Less Arctic Sea Ice Retreat but No Recovery
The Arctic Ocean reached its minimum sea-ice extent in mid-September 2009, the third lowest since the start of satellite measurements 30 years ago. While this year's ice cover was more than the record and near-record minimums of the last two years, it was still 1.28 million square km or 20 per cent below the 1979-to-2008 average, further reinforcing the strong negative trend in summertime ice extent observed over the past three decades.
In Canadian waters, sea ice extent was similar to that of 2008, but its spatial distribution was different. According to the Canadian Ice Service, greater-than-normal concentrations of ice occurred in the southeastern Beaufort Sea under prevailing northerly winds that carried some of the multi-year pack ice southwards. In the central and western parts of the Northwest Passage, thicker and more extensive ice led to delays in navigability of the southern route, while the northern route did not become truly navigable at all. By contrast, both routes were navigable in the summers of 2007 and 2008. Despite the increased ice cover, there was a record number of vessels plying the Northwest Passage – from cruise to cargo ships and a row boat or two – no doubt in response to greater interest by adventurers and commercial concerns. Increasingly, more ice in the Northwest Passage consists of orphaned chunks of the thickest, oldest “multi-year” ice mass that has been steadily disintegrating and flowing more easily into the channels, preventing regular openings. This year, the Northeast Passage along the Siberia coast opened sufficiently that two German heavy-lift ships successfully traversed from Korea to Novyi Port in the Russian Federation with ice-breaker support.
In the eastern Canadian Arctic, ice concentrations were for the most part well below normal while, as the result of summer coolness in central Canada, ice in southern sections of Hudson Bay persisted right until the end of August – a month later than normal. Along the north coast of Ellesmere Island, because no open water leads developed this year, there were no further losses to the ice shelves and no new ice islands. The estimated number of icebergs drifting south of latitude 48°N into the trans-Atlantic shipping lanes was 1204, the most in 10 years, making the iceberg season the eleventh most severe since the tragic loss of the RMS Titanic in 1912.
The Arctic sea ice decline was slowed in 2009 for several reasons. Summer air and surface sea temperatures were still warmer than normal but cooler compared to 2007, especially in the Chukchi and Beaufort seas. Further, skies were cloudier in late summer – which slowed ice loss – and the wind pattern tended to spread the ice pack over a larger region but not export it out of the Arctic Ocean.
According to the National Snow and Ice Data Center in Boulder, Colorado, seasonal ice is now dominating the North, while the traditional thicker, perennial ice has decayed significantly. Today, close to 80 per cent of the Arctic sea ice is new, weaker, salty and less than a year old. Further, old, durable multi-year ice is slowly thinning, is more broken-up and is moving faster which all contributes to melting earlier in the season.
The Arctic’s once perennial ice cover is becoming more seasonal and this is having an immediate impact on northern peoples. However, its effects on weather elsewhere are largely uncertain but potentially worrisome. Scientists cannot rule out the effects of vanishing ice on prolonged dryness in North America’s Great Plains or cooling of the Gulf Stream. A warmed Arctic Ocean emits heat into the atmosphere that can drastically alter weather patterns. The Arctic is the world’s refrigerator and is a key factor in stabilizing global climates. As a greater portion of the ice melts, larger expanses of darker-coloured sea water are exposed, absorbing more sunlight. An increase of just a few degrees – or even a fraction of a degree – can mean the difference between freeze and thaw, amplifying the warming in the North. This is why the Arctic is warming about three times faster than the global rate.
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