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
In one area in particular, Inuit hunters are helping inform local
weather record-keepers about a phenomenon occurring in the sky.
Davidson, a local weather station operator in Resolute Bay, Canada,
began measuring the change in the amount of twilight during cold
"I set out to prove that there was such a thing as global
warming through the optical route, which is kind of unique,"
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
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.
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
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,"
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.