Arctic to be ice free in summer – Consequences for polar bears

As the Arctic sea-ice receds in summer, what will happen to the bears? Copyright Wildife Extra.

October 2009. New data, released by the Catlin Arctic Survey and WWF, provides further evidence of thinning Arctic sea ice, supporting the emerging thinking that the Arctic Ocean will be largely ice-free in summer within a decade. The Catlin Arctic Survey provides the latest ice thickness record, drawn from the only survey capturing surface measurements in the last winter and spring. But what will be the consequences for Polar bears?

Beaufort Sea now all new ice
The data collected by manual drilling and observations on a 450 kilometre route across the northern part of the Beaufort Sea suggests the survey area is comprised almost exclusively of first year ice. This is a significant finding because the region has traditionally contained older, thicker multi-year ice. The average thickness of the ice-floes measured 1.8 metres, a depth considered too thin to survive the next summer's ice melt.

The findings were analysed by the Polar Ocean Physics Group at the University of Cambridge, led by Professor Peter Wadhams, one of the world's leading experts on sea ice cover in the North Pole region.

"With a larger part of the region now first year ice, it is clearly more vulnerable," said Professor Wadhams. "The area is now more likely to become open water each summer, bringing forward the potential date when the summer sea ice will be completely gone.

"The Catlin Arctic Survey data supports the new consensus view, based on seasonal variation of ice extent and thickness, changes in temperatures, winds and especially ice composition, that the Arctic will be ice-free in summer within about 20 years, and that much of the decrease will be happening within 10 years.

Open for shipping in summer
"That means you'll be able to treat the Arctic as if it were essentially an open sea in the summer and have transport across the Arctic Ocean."

According to the scientists who have studied the data, the technique used by the explorers to take measurements on the surface of the ice has the potential to help ice modellers to refine predictions about the future survival or decline of the ice.

Vast carbon release will follow tundra thawing
The results of the analysis of more than 6000 measurements and observations collected by the survey in 73 days on the ice were unveiled today in London with warnings that rapid climate change in the Arctic risked the release of vast quantities of carbon stored in hydrates on the Arctic seabed or in frozen tundra soils.

"The arctic sea ice holds a central position in our Earth's climate system. Take it out of the equation and we are left with a dramatically warmer world," said Dr. Martin Sommerkorn from the WWF International Arctic Programme, which was a partner in the survey.

Accelerating global warming
"Such a loss of Arctic sea ice cover has recently been assessed to set in motion powerful climate feedbacks which will have an impact far beyond the Arctic itself - self perpetuating cycles, amplifying and accelerating the consequences of global warming. This could lead to flooding affecting one quarter of the world's population, substantial increases in greenhouse gas emissions from massive carbon pools, and extreme global weather changes."

There are already signs of pressure on Polar bear populations due to the reduction in Arctic sea ice. Copyright Wldlife Extra.

"These findings provide yet another urgent call for action to world leaders ahead of the UN climate summit in Copenhagen this December to rapidly and effectively curb global greenhouse gas emissions, with rich countries committing to reduce emissions by 40% by 2020."

Consequences for polar bears
Polar bears are tied to the sea ice for nearly all of their life cycle functions. Most important of these is foraging, or access to food. Polar bears almost exclusively eat seals, and they are equally as dependent upon the sea for their nutrition as seals, whales, and other aquatic mammals. Polar bears are not aquatic, however, and their only access to the seals is from the surface of the sea ice. Over the past 25 years, the summer sea ice melt period has lengthened, and summer sea ice cover has declined by over half a million square miles. In winter, although sea ice extent has not changed as greatly, there have been dramatic reductions in the amount of old ice, predominantly in the western Arctic.

Because of their dependence upon the sea ice for food, these
changes can directly affect the carrying capacity of the Arctic for polar bears. USGS studies are documenting numerical responses to these changes in sea ice.

Lack of sea ice has reduced Polar bear numbers and led to cannibalism
In Western Hudson Bay near the southern extent of the range of polar bears, the Canadian Wildlife Service has long term data on population characteristics and changes in sea ice. Analysis of those data has shown that longer ice-free seasons have resulted in reduced survival of young and old polar bears and a population decline over the past 20 years.

Recent observations of cannibalism and unexpected mortalities of prime age polar bears in Alaska are consistent with a population undergoing change. Ongoing studies are designed to gain an understanding of movement patterns of polar bears in response to changing ice conditions and of associated population responses. If it is known how polar bears respond, functionally and numerically, to ice quantity and quality, we will be able to predict how forecasted changes in the ice may affect future polar bear populations. This will give managers the best chance of adapting strategies to assure long term polar bear survival in a changing ice environment.