The biggest threat to polar bears is the melting of Arctic Ice due to global warming. As humans are increasing the amounts of CO2 and other greenhouse gases into the environment, global warming begins to take place, and an increase in temperature is observed globally.
The biggest threat to polar bears is the loss and melting of sea ice habitat which is a direct result of global warming. The Arctic is warming a lot faster than many other parts of the world and leads to a change or alternation of habitat (Molnar et al 2010). The sea ice is melting at a much higher rate than scientists had predicted, and these rates are expected to increase in the near future. Sea ice in the Arctic has been melting 3% each decade which is equivalent to approximately one million square kilometers (National Snow and Ice Data Center, NSIDC ). Because of this, much of the polar bears critical habitat is already lost and will continue to melt unless we find a way to protect the polar bear’s habitat from the effects of global warming. The graph below from the National Snow and Ice Data center shows the average decline of sea ice at 3% per decade from 1979 to 2011.
 |
| Average melting of Arctic Sea ice from 1979 to 2011. |
If current greenhouse gas emissions continue, then two- thirds of the world’s polar bears will be extinct by 2050, including all of Alaska’s polar bears (Siegel et al., 2007). This is primarily due to global warming which is occurring much earlier and more intensely than predicted ( Siegel et al., 2007).
Polar bears are highly dependent on sea ice for breeding, catching prey, seasonal migrations and denning (Siegel et al. 2007). They spend majority of their lives on the sea ice traveling, foraging, searing for mates, and relying on ice corridors for transportation from denning areas (Kovacs et al. 2010) While the females are in the denning areas, they usually fast for couple of months and relying on their previous fat storage. After emerging from their dens, they reply on sea ice access for catching their main prey, ringed seals. Polar bears are specialized for hunting ringed seals and bearded seals from sea ice surfaces as they make up an important component of the polar bear’s diets. However, seals are also facing challenges due to climate change and rapidly changing sea ice conditions. Harp, bearded, and ringed seals are expected to decline due to early break of the ice pack (Kovacs et al. 2010).
Delayed ice formation and earlier ice breaks-up increase the distances between ice and land. Polar bears reach hunting grounds by swimming between land and sea. Due to these reasons, polar bears have to swim larger distance leading to increased cannibalism, starvation rates, low and depleted fat stores, and lower reproduction and cub survival rates ( Amstrup et al.2006; Regehr et al. 2006; Aars et al. 2006). In some Artic areas, sea ice melts completely forcing the polar bears on shore where they use their accumulated body fat for energy (Hunter et. al 2010).
A new study recorded a female polar bear swimming continuously for nine days and traveling 687 km, or 427 miles to find ice floes (Davies,2011). According to scientists, this long epic journey is a result of climate change. As sea ice continues to melt earlier each year, swimming long distances will be a growing trend for polar bears.
The U.S. Geological Service further studied the future populations for polar bears using a Bayesian Network model structure which incorporated the current greenhouse gas emissions, melting of sea ice, and other factors (USGS ). They made the following predictions:
1) In the Polar Basin Divergent and Seasonal Ice ecoregions (Alaska, North Canada, Hudson Bay, etc.) polar bears will be extinct by 2050.
2) In the Archipelago Ecoregion (Barents Sea, Chukchi Sea, Kara Sea, Laptev Sea, Southern Beaufort Sea, Canadian Archipelago, Greenland, High Canadian Arctic Islands, polar bears are still likely to persist mid-century. However, their numbers will be reduced mainly due loss of sea ice habitat and other factors
3) Polar Bears in the Polar Basin Convergent Ecoregion (Eastern Greenland, Northern Beaufort Sea, Queen Elizabeth Islands) will persist through mid-century but will most likely be extirpated near 2075.
The current population of polar bears in between 20,000-25,000 (US Fish and Wildlife Service). This number has increased since the 1960’s where the population was approximately 5,000 to 10,000 ( US Fish and Wildlife Service) Using the following projections and facts above I made the following figure which shows the historical increase in polar bear populations as well as the future predicted population trend.
 |
| Figure 1. Historic (Solid Lines). Projected (dotted lines). 1), 5) data was obtained from US Fish and Wildlife Service (See Reference 17, 25, and 26). (2), (3), (4), data obtained from US Geological Service Study of Polar Bears at Selected Times in the 21st century, 2007 (Reference 24). |
By mid-century polar bears from Alaska and the surroundings areas will be gone under the study done by the USGS. In all ecoregions, the population of polar bears is expected to decline. The reason: global warming.
