Polar bears are an international symbol of Canada and a barometer for what is happening in the climate-sensitive North. And according to wildlife experts now monitoring the impact of global warming in greater detail, the big bears aren't as big as they used to be.

The early breakup of sea ice and the longer period of open water have hindered their search for food, mostly seals. Not enough ice leads to less time hunting, less to eat – and shrinking bears.

The decline in size of the majestic bear was established by field workers recording their weight and length in the western Hudson Bay region, then comparing it with measurements taken in 1980.

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Female polar bears now weigh an average of 230 kilograms, or 507 pounds (they used to weigh 295 kg, or 650 pounds), and are 220 centimetres long, or nearly 7-foot-3 (they used to be 225 cm). Their skull size has also been reduced. The loss in weight can negatively affect the birthing of healthy cubs.

Some populations, such as those in western Hudson Bay and the southern Beaufort Sea, are already feeling the impact of climate warming.

These conclusions are based on decades of research on their population ecology. Other populations may be similarly affected but "they don't have adequate long-term data with which to address the question definitively," said Ian Stirling, an adjunct professor in biological sciences at the University of Alberta.

"However, the trends being illustrated in western Hudson Bay and the southern Beaufort Sea give us a clear indication of what is coming all over the circumpolar Arctic," Prof. Stirling added. "In 100 to 150 years, with no end to global warming, the polar bears will be having a very difficult time."

Currently, there are an estimated 20,000 to 25,000 polar bears worldwide, with 15,500 roaming about in Arctic Canada, searching for food.

"Climate change is certainly an issue for a northern animal whose habitat includes sea ice," said Justina Ray, a senior scientist at the Wildlife Conservation Society and co-chair for the Committee on the Status of Endangered Wildlife in Canada. "The question is how will polar bear populations respond across their distribution and are we able to project declines within a certain time frame? Where we are, right now, we have to watch [the polar bear] very closely."

In 2008, the committee labelled the polar bear a special concern and is mandated under the federal Species at Risk Act to review its status every decade. Environment Canada has legislated that review and offered funding for programs that study polar bears in sometimes traditional, sometimes alternative ways.

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The hot spot for polar bear observation and research is the U of A's biological sciences department. Andrew Derocher is a professor and former chairman of the Polar Bear Specialist Group. He worked with Prof. Stirling and co-authored a report called the Effects Of Climate Warming On Polar Bears: A Review Of The Evidence.

According to one aspect of the report, ice cover in the Arctic Ocean has decreased from roughly 75 per cent in the mid-1980s to 45 per cent in 2011. Changing conditions are changing the polar bear.

"Body condition is a reflection of fat stores and it is these stores that the bears rely upon for energy when they are onshore," Prof. Derocher said. "Declines in body condition are the precursor to other changes in a population as the sea ice continues to change."

Corey Davis is a faculty service officer for the U of A's bio sciences faculty who has just received a federal grant to investigate his area of expertise – hybrid bears dubbed Prizzlies or Grolars that are the offspring of female polar bears and male grizzlies.

"[Grizzlies] are moving further north where they can intermix with the female polar bears and hunt for food," Dr. Davis said. "We want to look at the frequency of the hybrid."

For his project, U of A PhD student René Malenfant helped design a special BeadChip to aid in the analysis of the "genetic population structure of the threatened Canadian polar bears in the Western Hudson Bay subpopulation."

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Data are extracted from the tissue samples provided when field workers ear-tag bears for scientific reference. Mr. Malenfant explained that the BeadChip could provide evidence to determine the population structure of polar bears as well as examining "the genetic architecture of body size differences in western Hudson Bay."

While experts argue back and forth over the polar bear's short-term and long-term fate, at least this much is agreed upon: The bears need to be monitored to maintain their lofty status as a unique representation of Canada – and a symbol of the need to protect their environment.

Just last week, thousands of activists gathered on New York's Wall Street and staged a protest. The sit-in had to do with big business making money at the expense of the planet. More than 100 protesters were arrested. One was a man dressed in a polar bear suit.

He made bail.