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Andrew Paterson, left, and Chris Jones collect sediment cores in the Hudson Bay Lowlands.

One of the last refuges from the effects of global warming in Canada's Arctic is succumbing to rising temperatures, creating significant risks for polar bears and the people who must survive off a rapidly transforming landscape.

A team of five researchers from Queen's University, Laurentian University and the Ontario Ministry of the Environment has looked at algae deposits in lake sediments in the Hudson Bay Lowlands over the past 70 years and determined that, since the mid-1990s, the area has warmed dramatically.

In a paper released Tuesday, they say their research provides evidence "that we are witnessing the transformation of the Arctic at an exceptional pace."

The research follows a report of the Intergovernmental Panel on Climate Change in late September in which climate scientists said they were more certain than ever that human activity is the leading cause of global warming and that its effects will linger for centuries.

John Smol, a paleolimnologist at Queen's who was one of the authors of the new study of the Hudson Bay Lowlands, has been working in the Arctic for 30 years.

In all that time, he said in a telephone interview on Tuesday, he has had to qualify his observations that the region is warming by saying there were a few isolated areas where the climate was not varying significantly. They included the Hudson Bay Lowlands, a sprawling wetland on the southern shore of Hudson Bay that is home to Canada's southernmost polar bear population.

Ice that was locked into Hudson Bay kept annual temperatures stable, said Dr. Smol. But scientific experts had long predicted that the lowlands would eventually start warming along with the rest of the North and now scientists can see that happening, he said.

"We all know that the Arctic is the miner's canary of the planet," Dr. Smol said. "It is the first to show signs of environmental change, and to the greatest degree. Soon we won't have to say almost all areas of the Arctic have been warming because, here, one of the last big refugia seems to have succumbed."

The first real hint that the Hudson Bay Lowlands were heating up came in 2001 when massive numbers of brook char were found dead, apparently from thermal stress, in the Sutton River. That river flows into Hawley Lake, which is one of the places where Dr. Smol and his team sampled cores of sediment in the summers of 2009 and 2010.

They were looking at all of the biological matter that had collected on the lake beds going back, in some cases, as far as two centuries. In particular, they were looking for diatoms, which are algae that come in hundreds of different species.

Some of the species of diatoms like frigid Arctic lakes and others prefer warmer waters. The scientists found that while there had been little change for 200 years, in 1995 the warm-weather diatoms suddenly and markedly started becoming more abundant.

That reflects warming that took place, not just in the lakes, but in the entire ecosystem, Dr. Smol said.

"This is the second-biggest peatland in the world. That has all sorts of implications for global warming. What were once sinks for greenhouse gas are now going to start drying up and decomposing," he said.

It is also an ecologically distinct area. The population of polar bears is totally dependent on the Hudson Bay sea ice. And the hunting and fishing routes of the local aboriginal population are likely to be affected, say the scientists.

The IPCC report pointed out that the Earth's atmosphere has warmed less over the past 15 years than most climate models anticipated – something skeptics have latched onto to suggest that scientists are wrong in their dire predictions of global warming.

But, over that same 15-year period, Dr. Smol said, the Hudson Bay Lowlands have demonstrated a dramatic impact. And "even though the rate of global warming has been lower than expected, the planet "is still warming. The last decade was still warmer than the decade before," he said. "The implications are we have to start doing something."