Weather: What happens to the Arctic climate affects us!

Sunday, January 10, 2010

Loss of Arctic ice cover isn't just bad news for polar bears and seals. It has a direct bearing on weather patterns in Ontario

by HENRY HENGEVELD

Minimum Arctic sea ice cover during this past summer was once again well below the average of the past 30 years – in fact, about 23 per cent below. While not as low as the record set in 2007, this is now the third consecutive year that minimum sea ice cover has been well below normal, and the continuation of a rapid downward trend that began more than a decade ago. 

Ice experts are not surprised by the decline. After all, most climate models suggest that, as the earth continues to warm in response to rising atmospheric greenhouse gas concentrations, Arctic Ocean ice cover will eventually completely disappear in late summer. Some models project this could occur within the next 50 years.

However, researchers are baffled by how significant the decline has been in recent years. Some now speculate that the delicate Arctic climate system may have passed a critical threshold beyond which summer ice cover may no longer be sustainable. If so, summer ice may disappear much sooner than we thought.

Loss of ice cover will have major implications for the Arctic environment and the Inuit way of life. It already has. That's bad news for polar bears and seals, but good news for ocean species that need open water to survive. It will also, eventually, open up the Northwest Passage to increased commercial shipping, bringing positive economic opportunities, but also concerns about sovereignty and the increased potential for environmental disasters. 

Less well recognized, however, is that loss of Arctic ice cover will also affect weather in Ontario. Yes, in Ontario!

Arctic ice acts like a buffer between the atmosphere and the surface waters of northern oceans. In the summer, when the sun shines non-stop, reduced ice cover significantly increases the absorption of sunlight into the dark surface of the ocean. This increases the ocean heat content and helps delay fall freeze-up. Rising air temperatures add to this delay.

During the following winter, the ice that does form is thinner. Furthermore, in marginal waters such as the Labrador Sea, Hudson Bay and the Greenland Sea, the winter ice becomes less concentrated.

The thinner and less extensive ice cover allows much more heat and moisture to escape from the oceans into the cold atmosphere above, causing the atmosphere to warm much more than it would without the ice cover decrease. This regional warming can significantly alter the circulation of the atmosphere through the hemisphere. 

Past research has already shown that, as the atmospheric circulation changes in response to warmer climates, storm tracks throughout the Northern Hemisphere will push further north, increasing precipitation in sub-Arctic and Arctic regions and decreasing storm events further south. There are also indications that, while the total number of winter storms in mid-latitudes appears likely to decrease, the number of intense storms may actually increase. 

However, now it seems that the change in sea ice concentrations may also have direct effects on the North Atlantic Oscillation (NAO) behaviour, which is one of the circulation features that can significantly affect weather in Ontario.

Several months ago, in a research paper published in the scientific journal Climate Dynamic, Norwegian scientists described how the change in Arctic winter ice cover might be linked to NAO behaviour. They ran a weather forecasting model with two sets of ice conditions, one like that for current winters, the other with reduced ice cover similar to that projected under global warming scenarios for the end of this century.

Not surprisingly, results showed a large increase in ocean heat escaping into the atmosphere over Arctic regions during winter months when ice conditions were much reduced. While this had only modest effects on the NAO during early and mid-winter months, it caused a large change in March. The circulation changes, in turn, caused reduced March storminess in mid-latitudes. 

The researchers involved in the study were not sure, based on their experiment, why the response of mid-latitude storminess to sea ice cover was much stronger in March than in December through February. However, they note that others have found similar results with other models. They plan to find out in future studies.

These early results provide us with one more indication that what happens to our climate system at the top of the world also affects us. Further, what we now think of as "normal" climate just won't be normal in the decades to come! BF

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