From the thinning Arctic sea ice to the softening permafrost and the northern migration of indigenous animals, scientists and Arctic dwellers are taking note of the gradual impacts of climate change.

In one area in particular, Inuit hunters are helping inform local weather record-keepers about a phenomenon occurring in the sky.

Wayne Davidson, a local weather station operator in Resolute Bay, Canada, began measuring the change in the amount of twilight during cold winter months.

"I set out to prove that there was such a thing as global warming through the optical route, which is kind of unique," he said.

Davidson first hypothesized that global warming would cause a darkening of the sky at night. He later reversed his conjecture after hearing from local Inuit hunters, who insisted that the winter night sky was growing progressively brighter.

"Because they go out hunting at night, they need to see where they're going. So if they see more than they used to, they would know right away," he explained.

Armed with this anecdotal information and his own observations, Davidson determined that a warm layer of air was reflecting light from the sun over the horizon. And some say this warm layer of air could be caused by global warming.

But to understand why the sky may be growing lighter, Davidson and other researchers needed to better understand the atmospheric conditions.

During regular conditions within the troposphere -- the bottom layer of the atmosphere closest to the Earth's surface -- temperature declines with elevation. In other words, the higher you go, the colder you get, because the Earth's surface absorbs solar energy and heats the air immediately above it.

Under certain conditions the opposite can occur, creating a "temperature inversion." That means a colder layer of air close to the Earth's surface lies below a warmer layer. Normally this phenomenon is temporary, but if the Earth's surface doesn't warm up from the sunshine quickly or in the absence of a steady wind, it can last for a long time.

"Cold air doesn't particularly want to rise -- no body has ever heard of a cold air balloon -- so basically you end up with what you call stable air," said Alan Osborn, a physical geography professor at San Diego State University.

Only when the temperature difference is big enough can light rays from the sun -- which has already fallen below the horizon -- bend back toward the Earth to light up the night sky. Davidson likens the temperature inversion to fiber optics, capturing the light and carrying it back to the ground.

Temperature inversions can occur on a large scale in cities when a higher layer of warm air traps smog close to the city surface.

"If you're talking about an industrial area, you can get a buildup of pollution, and that's one of the reasons that major cities end up with rather nasty pollution situations," Osborn said.

Although reports from the American Association for the Advancement of Science in December 2006 and the Intergovernmental Panel on Climate Change in February 2007 have linked global warming -- "likely" due to human causes -- to melting glaciers and rising sea levels, the verdict is still out on its influence on thermal inversions.

According to Edward Aguado, professor of climatology at San Diego State University, global warming cannot account for the sudden appearance of a temperature inversion. "I'm not inclined to attribute any short-term data to global warming. You can't say that it's because of global warming. You'll have anomalous years where the temperature jumps. But what you'll get perhaps is a greater incidence of warm years over a period of time," Aguado said.

Still others question the validity of anecdotal evidence in proving the effects of global warming. Roger Barry, director of the National Snow and Ice Data Center, and Canadian climatologist Shari Gearheard, have been interviewing indigenous Inuit tribes across northern Alaska and Canada. Although their findings support other research pinning global warming as the cause of Arctic changes, Barry acknowledges the difficulty with using anecdotal evidence.

"It is partly due to a scale problem. Observations are at a local scale, we are dealing with a bigger scale of pictures, and there is variability at a smaller scale," he said.

However, whether observing changes in the night sky or watching melting ice on the ground, many scientists agree it is the Arctic -- and Antarctica -- that reflect the changing climate and are the hardest hit by global warming. And the local populations in the North are intimately connected to these changes.

-- By Edward Kim, Online NewsHour