Weather: The number one weather story for 2007 - disappearing Arctic ice

Friday, February 29, 2008

Last year, the already shrinking summer Arctic ice diminished even more dramatically, as did the Greenland ice sheet, making it Environment Canada's choice for number one weather story of the year

by HENRY HENGEVELD

The world's climate number crunchers - including Environment Canada's David Phillips and Bob Whitewood - once again spent the early days of January in putting together annual weather statistics for 2007. The results that emerged from their analyses included a lot of the same old, same old - but also provided a few interesting anecdotes that will undoubtedly become part of our climate lore.

For the Earth as a whole, average surface temperatures for 2007 were about 0.37 C above the norm. While not as warm as the previous few years, this places 2007 among the 10 warmest years on record. Weather watchers indicate that the slightly cooler conditions in 2007 relative to the previous year are largely due to the influence of the strong La Nina now underway in the tropical Pacific, a short-term cooling influence that will also likely keep 2008 from setting new records.

Munich Re, the world's second largest re-insurance company, reported in its year-end assessment that total global property losses during 2007 due to natural disasters - mostly weather-related - rose to $75 billion, some 50 per cent higher than in 2006. Insured losses doubled to $30 billion. The high losses were due to the record number of disasters - about 950 multi-million-dollar events - which occurred during the year. One of these events, Cyclone Sidr, also caused killed an estimated 3,300 people when it struck Bangladesh and India in November.

Munich Re officials note that the high losses in 2007 are consistent with the long-term global trend towards more intense and frequent extreme weather events and suggested that this trend demonstrates that climate change is already taking effect. They warn that the number and intensity of such extremes - and related property losses - can be expected to continue to rise in the future.

Another major global climate news story for 2007 was that of the disappearing ice and snow in the Arctic.

For several years, the extent of summer ice across the Arctic Ocean has become less and less. In September of 2005, it had set a new record low of 5.3 million square kilometres. However, in 2007, it had dramatically shrunk even further, to about four million square kilometres. For a short period of time, the North West Passage was virtually ice-free.

Researchers monitoring the Greenland ice sheet have noted that the extent of melt across the ice sheet was also 10 per cent greater than the previous record set in 2005. This, too, appears to be a part of a long-term trend. In western Greenland, for example, the extent of surface melt in 2007 was about 30 per cent greater than in 1996.

However, in addition to increased surface melt, experts have also observed a dramatic increase in glacial flow from the margins of the ice sheets into the surrounding oceans. This acceleration already began in southern Greenland during the late 1990s, but has now extended much further north. Total volume of Greenland ice now melting and sliding off into the ocean each year has more than doubled over the past decade, with net losses in 2005 exceeding 200 cubic kilometres of ice. That's a lot of ice bergs!

This unprecedented reduction in Arctic Ocean ice cover and Greenland ice volume has surprised many experts, who had assumed that the ice retreat in response to warmer climates would be gradual. It appears that the progressive thinning of the Arctic sea ice under rising Arctic temperatures, together with the much higher absorption of sunlight by the open waters that replace the ice cover, increases the likelihood of a sudden collapse. Experts now suggest that an ice-free Arctic Ocean in summer may occur decades sooner that previously projected.

Average temperatures across Canada during 2007 also continued to be warmer than normal. At 0.9 C above the 1961-90 norms, it was the 13th warmest since nationwide monitoring began in 1948. While no region in Canada set new record high temperatures, the above normal conditions prevailed throughout all parts of the country. In the Great Lakes basin of Ontario, temperatures were some 0.7 C above the norm.

There were also few surprises with respect to average precipitation. Nationwide, precipitation was 3.3 per cent above normal. Despite the dry summer in parts of southern Ontario, the yearly average precipitation for the entire Canadian Great Lakes region also wasn't that unusual - about 6.6 per cent below the norm.

There were, of course, the weather "events" during the year that provided fascinating material for discussions at social gatherings and around the kitchen tables. In his annual "top weather stories" summary, Dave Phillips highlights a few of these. His number one 2007 weather story for Canada was the disappearing Arctic sea ice, selected both because of its unusualness and its long-term significance for global weather.

However, every corner of the country can claim its own story. For example, in interior B.C., the big local story was high flood waters during the spring thaw. In the Prairies, it was the unusually hot and steamy summer and the record number of hailstorms (a total of 410 events) which resulted in an estimated $115 million in insurance payouts for crop damage. In Atlantic Canada, it was heavy rains from tropical storm Noel. Manitoba had its worst ever F5 tornado (although, despite its ferocity, it caused no human injuries).

In Ontario, one of the main weather stories was the extended drought in southern regions. While the dry, sunny weather was great for vacationers and the fruit industry, the long drought left many farm crops withered and dry and stressed natural vegetation across a broad region between Chatham and Peterborough.

Another, not unrelated, story was the dramatic drop in water levels of the Great Lakes, particularly for Lake Superior and the St. Lawrence River. That's the way it was, in 2007. BF

Henry Hengeveld is Emeritus Associate, Science Assessment and Integration Branch/ACSD/MSC, Environment Canada.