Melting kindom of the polar bear: Polar bear's survival under the global warming

Tuesday, November 29, 2011

Polar bear's survival under the global warming

The polar bear, Ursus maritimus, or the sea bear, evolved about 200,000 years ago from brown bear ancestors. They are superbly adapted for survival in the Far North.

Photograph by Norbert Rosing

Polar bears range throughout the Arctic in areas where they huntseals at openings in sea ice called leads. Five nations have polar bear populations: the United States (Alaska), Canada, Russia, Denmark (Greenland), and Norway.

From Sierra Club

At the March 2009 range states meeting of the five polar bear nations, scientists agreed that climate change is the single biggest threat facing polar bears.

The Arctic is experiencing the warmest air temperatures in four centuries. The Arctic has experienced warm periods before, but the present, rapid shrinking of sea ice is unprecedented. Scientists predict a mostly ice-free Arctic summer by 2040 if present trends continue.

From Peas in a pod, Peapod's blog

Today's polar bears are facing rapid loss of the sea ice where they hunt, breed, and, in some cases, den. Changes in their distribution or numbers affect the entire arctic ecosystem.

Scientists believe that we still have time to save polar bears if we significantly reduce greenhouse emissions within the next few years. Yet it will take 30 to 40 years for changes reversing the warming trend to show.

Polar bears are finding too much open water. In 2004, four polar bears drowned off the coast of Alaska when trying to swim to the pack ice.

Nikita, Ovsyanikov. Polar Bears : Living with the White Bear / Nikita Ovsyanikov. Stillwater, Minn: Voyageur Press, 1996.

http://www.actionbioscience.org/environment/derocher.html
http://www.pitara.com/discover/earth/online.asp?story=140&page=2
http://e360.yale.edu/content/feature.msp?id=2161
http://www.seaworld.org/animal-info/info-books/polar-bear/habitat-&-distribution.htm

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What does global warming have to do with the decline in the polar bear population?

The largest carnivores on land are getting squashed like tiny bugs. Measuring up to 10 feet tall (3 meters) and weighing in at up to 1,700 pounds (771 kilograms) polar bears are formidable creatures. But the massive animals are struggling with a global predator -- climate change -- and they're losing.Scientists have been talking about melting polar ice caps and rising sea levels for decades. Now, it's not just talk. The average temperature in the Canadian Arctic has risen 7 degrees Farenheit (4 degrees Celsius) in the last 50 years [source: Daily Mail]. Temperatures in the Arctic Circle are increasing at twice the rate of the rest of the world's climate [source: Yahoo News]. The Arctic ice is melting, and the seas are becoming more treacherous. This is bad news for polar bears.The polar bear habitat is about as frigid as it gets, and the animals are ideally suited to survive in the tough environment. They have several inches of both fur and blubber to insulate them from temperatures that drop to -49 Fahrenheit (-45 Celsius) in the dead of the Arctic winter. They've evolved to thrive under these conditions.But what happens to a species when its ideal habitat starts to disappear? As we'll find out in the next section, it's not pretty at all.
http://www.skepticalscience.com/polar-bears-global-warming.htm

How will global warming affect polar bears

What the science says...
Polar
bears are in danger of extinction as well as many other species.
Polar bears are found in the Arctic circle and surrounding land masses. There
are 19 recognised subpopulations, and estimates place their numbers at about
20,000 to 25,000. Polar bears are classed as vulnerable by the World Conservation Union (IUCN)
and listed as a threatened species under the US Endangered Species Act. Yet some
claim that polar bear numbers have increased since the 1950s and are now stable.
So what is the situation for this species?
First of all, a few points need to be made about polar bear numbers:
Nobody really knows how many bears there were in the 1950s and 1960s.
Estimates then were based on anecdotal evidence provided by hunters or explorers
and not by scientific surveys.
Polar bears are affected by several factors, including hunting, pollution
and oil extraction. Most notably, hunting, particularly following the
introduction of snowmobiles, airplanes and ice breakers, led to a huge decline
in certain subpopulations. The introduction of the International Agreement on
the Conservation of Polar Bears in 1973, which restricted or even banned hunting
in some circumstances, consequently resulted in an increase in polar bear
numbers.
Not all subpopulations are affected to the same degree by climate change,
and while some subpopulations are well studied, for others there is insufficient
data to make broad statements about current and past numbers.
With this caveat in mind, what do the figures actually say? According to a
2009 report by the IUCN Polar Bear Specialist Group, of the 19 recognised
subpopulations of polar bears, 8 are in decline, 1 is increasing, 3 are stable
and 7 don’t have enough data to draw any conclusions. Figure 1 below compares
the data for 2005 and 2009.

Figure 1: Subpopulation status of polar bears for 2005 and 2009 (Source:
Polar Bear Specialist
Group)
Both habitat degradation and over-harvesting are responsible for the decline
in some subpopulations. To understand why the IUCN and US Endangered Species Act
consider polar bears to be at risk, it is important to look at how rising
temperatures are likely to affect their habitat in the future. Polar bears are
highly specialised mammals which rely heavily on sea ice for food and other
aspects of their life cycle. Satellite data show that Arctic sea ice has been
decreasing for the past 30 years, and projections show that this trend will
continue as temperatures carry on rising. The changes in sea ice affect polar
bears in several ways:
The early retreat of summer sea ice means that bears have less time to hunt
and therefore less time to build up fat reserves.
The fragmentation and reduction in sea ice has several impacts. It forces
the bears to swim longer distances, using up some of their fat reserves. It also
reduces the number of seals, which are the bears’ main source of food, and
impedes travelling and den making. And it also forces the bears to spend more
time on land, with increased interactions with humans potentially leading to
higher mortality.
To get an idea of the potential impacts of future climate change on polar
bears, we can look at subpopulations found at the bears’ southern range, where
habitat changes have been most noticeable so far. A good example is the western
Hudson Bay subpopulation, which is one of the best studied. Here, ice floe
break-up is taking place earlier than 30 years ago, effectively reducing the
feeding period by about three weeks. As a result, the average weight of female
polar bears has dropped by about 21% between 1980 and 2004, and the population
declined by 22% between 1987 and 2004. In Alaska, there is evidence of increased
cub mortality caused by a decline in sea ice.
In conclusion, the reason polar bears have been classed as threatened comes
from the impacts of future climate change on the bears’ habitat. Current
analysis of subpopulations where data is sufficient clearly shows that those
subpopulations are mainly in decline. Further habitat degradation will increase
the threats to polar bears.
http://earthtrends.wri.org/updates/node/138

Melting kindom of the polar bear

Melting Arctic Sea Ice Threatens Polar Bears

Tuesday, November 29, 2011

Polar bear's survival under the global warming

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