Polar Bear Population Declines Because It's Getting Too Hot

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December 15, 2015 | 10,604 views

Story at-a-glance

  • One-third of wild polar bears may be in imminent danger of population declines within the next 10 years
  • As temperatures rise, the sea that ice polar bears depend on to hunt is disappearing, leaving them without a steady food source
  • Polar bear populations may continue to decline unless aggressive reductions in greenhouse gas emissions are made

By Dr. Becker

Polar bears are uniquely suited to survive in the frozen Arctic tundra. Their double layer of fur and thick fat stores keep them warm even in temperatures that reach -50 degrees F.

Their slightly webbed front paws, complete with small bumps to give them traction (known as papillae), are perfect for swimming in the frigid seas and traveling on slippery sea ice.

But even with these survival advantages, “polar bears are in big trouble,” said Rebecca Noblin, Alaska director for the Center for Biological Diversity, in the Associated Press.1

There are only an estimated 22,000 to 25,000 polar bears left worldwide, and one-third of these may be in “imminent danger” within the next 10 years, according to a government report released as part of the U.S. Fish and Wildlife Service's recovery plan for the polar bear.

Diminishing Sea Ice Could Put Polar Bears at Risk

The report used updated scientific models to predict the effects of climate change on polar bears. One scenario used a model in which greenhouse gas emissions, which are widely blamed for climate warming, stabilized while the other model included worsening greenhouse gas emissions.

In both cases, polar bears in Alaska, Russia, and Norway, a population of about 8,500 bears, could be affected as soon as 2025.2 These regions have seen some of the worst declines in sea ice during the summer months.

Polar bears depend on ice floes (floating ice) to hunt seal, mate, and give birth. As the sea ice melts, the bears may be forced onto land, where food is scarce. On shore, the bears resort to eating goose eggs and even human trash, which may give them a small nutritional boost but is unlikely to sustain the species as a whole over time. As reported in the journal Frontiers in Ecology and the Environment:3

“Only small numbers of polar bears have been documented consuming terrestrial foods even in modest quantities. Over much of the polar bear's range, limited terrestrial food availability supports only low densities of much smaller, resident brown bears, … which use low-quality resources more efficiently and may compete with polar bears in these areas.

Where consumption of terrestrial foods has been documented, polar bear body condition and survival rates have declined even as land use has increased.

Thus far, observed consumption of terrestrial food by polar bears has been insufficient to offset lost ice-based hunting opportunities but can have ecological consequences for other species. Warming-induced loss of sea ice remains the primary threat faced by polar bears.”

The melting sea ice may also be encouraging the bears to spend more time in the water. In Svalbard (part of the Norwegian archipelagos), researchers documented a record-breaking polar bear dive – three minutes and 10 seconds – made by an emaciated polar bear hunting a seal.4 The researchers believe the long dive may indicate the bears are resorting to extreme survival measures as climate change leads to less available ice.

All Polar Bear Populations May Continue to Decline

Even if emissions are reduced, the researchers believe all polar bear populations may continue to decline, although this may stave off decreases in some populations for another 25 years.

However, if emissions levels continue unabated it could lengthen the summer ice-free period beyond four months by the last half of this century. If this happens, the “negative effects on polar bears will be more pronounced.” Todd Atwood, research biologist with the U.S. Geological Survey (USGS), and lead author of the study, explained:5

“Substantial sea ice loss and expected declines in the availability of marine prey that polar bears eat are the most important specific reasons for the increasingly worse outlook for polar bear populations.

… We found that other environmental stressors such as trans-Arctic shipping, oil and gas exploration, disease and contaminants, sustainable harvest, and defense of life takes, had only negligible effects on polar bear populations — compared to the much larger effects of sea ice loss and associated declines in their ability to access prey.”

Is There Hope for Threatened Polar Bears?

The U.S. Fish and Wildlife Service listed the polar bear as threatened under the Endangered Species Act in 2008. According to the USGS report, the bears’ population may continue to decline unless “aggressive reductions” in emissions are made:6

“USGS scientists’ research found that managing threats other than greenhouse gas emissions could slow the progression of polar bear populations to an increasingly worse status.

The most optimistic prognosis for polar bears would require immediate and aggressive reductions of greenhouse gas emissions that would limit global warming to less than 2°C above preindustrial levels.”

Taking action against greenhouse gas emissions must be done on a global scale, however there are steps you can take on an individual level as well. If you’d like to help polar bears, Polar Bears International recommends taking part in local “green” initiatives like planting trees, recycling, and biking to work as well as conserving energy when you can by using LED light bulbs and energy-efficient appliances.7

They also recommend consuming products like pasture-fed beef, free-range poultry and wild salmon rather than CAFO (concentrated animal feeding operations) meats. CAFOs (and genetically modified crops) play a significant role in greenhouse gas emissions, as they release more greenhouse gases into the atmosphere than the entire global transportation industry.

The conversion of croplands to grasslands significantly reduces annual greenhouse gas emissions, as do simple natural farming methods, like composting.

It's estimated that compost made from California's green waste, which includes household food scraps, dairy manure, and more, could absorb 75 percent of the state's greenhouse gas emissions for one year if applied to just 25 percent of the state's rangeland.8

So supporting small, local farmers raising animals on pasture, and composting their waste, may be one of the most powerful individual strategies you can take to help save the polar bears.

[+]Sources and References [-]Sources and References

  • 1, 2 Associated Press July 2, 2015
  • 3 Frontiers in Ecology and the Environment 13: 138–145.
  • 4 Polar Biology August 2015
  • 5, 6 U.S. Geological Survey June 30, 2015
  • 7 Polar Bear International, How to Help Polar Bears
  • 8 SF Gate October 31, 2014