‘Rotten’ multi-year ice

February 11, 2010

in Canada, Science, The environment

Because of the tilt of the Earth, the polar regions will always be cold in the winter. What is changing in the Arctic is the amount of ice that can endure through the summer months. Ice that has survived two winters is said to be ‘multiyear’ ice. Because more salt has been forced out from it, it is harder than younger ice. That makes it more durable, as well as a greater hazard to ships. While the decline in the overall extent of Arctic sea ice has been dramatic, the decline in the extent of multiyear ice has been even more so. This animation shows it vanishing over the past 30 years.

Furthermore, at least some scientists believe that most of the melting taking place has been from the bottom, and anecdotal reports from people operating icebreaking ships suggest that the multiyear ice still out there isn’t the same thing as what existed before. It is riddled with brine channels and weaker, and sometimes just consists of a thin layer of young ice covering small chunks of old ice. As such, it is more vulnerable to melting. This weak and vulnerable ice can provide a false impression of strength, when viewed from space. David Barber, Canada’s Research Chair in Arctic System Science at the University of Manitoba, has explained to Parliament that “we are almost out of multiyear sea ice in the northern hemisphere.”

While the loss of sea ice may be welcome to those seeking a transpolar shipping route, or the chance to drill for oil and gas, it is definitely bad news for the charismatic megafauna with lifestyles critically dependent on sea ice. Seals need it in order to rear their pups, while polar bears need it to hunt seals. The total loss of summer sea ice would probably spell the doom for both species in the wild.

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