This fall, polar bears gathered on the western shores of the Hudson Bay, waiting for sea ice that once again would free them from land, allowing them to hunt seals.

This timeless tableau on treeless salt marshes is changing. The “Lords of the Arctic,” North America’s largest land carnivores, are 10 percent thinner and have 10 percent fewer cubs than they did 20 years ago, reports the New York Times in a recent in-depth feature story.

The culprit, scientists and residents here said, is climate change. Today, on average, ice melts off the Hudson Bay three weeks earlier than 25 years ago. That means three weeks less each year for the polar bears to capture and gorge on seal pups.

And so the bay’s 1,200 polar bears, the world’s southernmost polar bear population, are fast becoming worldwide symbols of climate change, the Times reported.

In mid-November, protesters in The Hague dressed in sad-faced polar bear costumes and staged “die-ins” at opening sessions of negotiations over the Kyoto Protocol, a three-year-old international treaty intended to cut greenhouse gases.

By all indicators, ice in the western Hudson Bay is breaking up earlier as temperatures rise. “The trend for earlier breakup is really important for polar bears, because the spring is when polar bears store most of their energy,” says one researcher at the Canadian Wildlife Service.

Since 1950, temperatures here have risen by half a degree Fahrenheit every decade. Scientists project temperatures will rise by 4 to 11 degrees this century. That means within 30 years this sub-Arctic treeless tundra region could shift to New England-style temperate leafy forest. “One of the forecasts is that we will eventually lose ice in the Hudson Bay,” said the wildlife researcher. “If that happens, we may lose bears in the bay.”