Will Polar Bears Die Out Because of Climate Change?

A polar bear in the Hudson Bay population. Photo credit: <a href="www.flickr.com/photos/32368927@N02/8185281699/in/photolist-dtiH5x-dtgZRm-dti3mr-dti5Xu-dthrBF-dtg4WR-dtgUVT-dtiEX7-dtiuSX-6yoKpU-dtim7q-aAi84H-dtisfB-xLBnC-dtiqyT-dtit6H-53fH9i-53fHWR-aA4qvZ-aA77NC-aA4njn-aA4o58-7V9V4v-8vp6Cv-dtiCF4-6nBQHJ-8vs8bq-8vsaLq-8vp6U8-dtiBZU-8vp5X4-aA4pN4-4gzhyU-8vs9Rb-c9pJiG-c9pJqj-59L5P-eXHm71-596wZK-YFsRP-6BtdC9-dti4gq-dtionZ-dti2e5-z2MhH-dtiNfL-R8Jo-dtiHiL-dtiAC2-5a7UjN-aAi4tr">Alex Berger</a> /Flickr through a Creative Commons license.

A polar bear in the Hudson Bay population. Photo credit: Alex Berger /Flickr through a Creative Commons license.

Editor’s note: “What Does the Science Say?” is a new Cool Green Science feature looking at what scientists and the scientific literature really say about big questions regarding nature and its conservation. 

By Lisa Feldkamp, senior coordinator, new science audiences, The Nature Conservancy

Everyone has heard that polar bears are threatened by climate change. But what does that mean, exactly? Will they eventually go extinct, morph into another species, or something else? What does the science really say?

The Topline: No Sea Ice, No Seals, No Polar Bears

As with most species that are or will be vulnerable to climate change, habitat is key in the case of the polar bear. Climate change is warming the Arctic along with the rest of the planet — and in the Arctic, that means sea ice is melting.

And sea ice is crucial for polar bears survival.

Why? Because polar bears’ main prey — seals — are best hunted on sea ice. Without sea ice, polar bears cannot catch enough seals to eat — and without enough seals to eat, they are unlikely to gain enough weight to survive their autumn to summer fast (Derocher 2013, Stirling 2012).

In addition, longer periods between successful hunts decrease polar bears’ reproductive success. A female polar bear who has not gained sufficient weight may not produce cubs; may produce less milk (leading to smaller, less viable cubs); or may abandon cubs — all behaviors that, if they become prevalent enough, will impact a population’s viability (Robbins 2012).

Most scientists agree that these trends spell likely trouble for polar bears.

There are 19 distinct subpopulations of polar bears living in the Arctic, and each population will be affected somewhat differently.

Without human intervention, most polar bear populations will be extinct in 30-40 years (Castro de la Guardia 2013, Stirling 2012)).

The populations of polar bears living farthest to the north (in the Canadian Arctic Islands, northern Greenland, and farther to the north) have actually seen population increases in recent years (Peacock 2013) and may survive indefinitely (Stirling 2012).

However, they will be at risk from continued climate fluctuation (Bechschoft 2011, Stirling 2012); contaminants in the Arctic (Bechshoft 2011, McKinney 2013); increased disease risk (Derocher 2013, Stirling 2012); and decreased genetic diversity (Stirling 2012).

But Can’t They Eat Something Else?

If nothing is done, lack of sea ice will force polar bears on land for longer periods of time. On land, bears “fast” eating some berries, eggs and birds (Iles 2013).

However, scientists’ opinions are mixed on whether these foods could provide enough added energy for the long-term survival of these large bears.

Bears would still need to get some food from hunting seals; the question is, how many calories could be offset by terrestrial sources?

A polar bear in the Hudson Bay. Photo Credit <a href="http://www.flickr.com/photos/32368927@N02/8185231823/in/photolist-dtisfB-xLBnC-aA4njn-7V9V4v-8vp6Cv-dtiCF4-6nBQHJ-8vs8bq-8vsaLq-8vp6U8-dtiBZU-8vp5X4-8vs9Rb-c9pJiG-c9pJqj-596wZK-6BtdC9-z2MhH-dtiNfL-dtiqyT-dtit6H-53fH9i-53fHWR-aA4qvZ-aA77NC-aA4o58-aA4pN4-4gzhyU-59L5P-eXHm71-YFsRP-dti4gq-dtionZ-dti2e5-R8Jo-dtiHiL-dtiAC2-5a7UjN-aAi4tr-tWcK-dGHzRY-cGFfLo-ddyj6g-6yjCXB-6yjAik-6BhMd5-64iCG2-aw7Ltx-eiJfnc-eiJyke-6iJ529">Alex Berger</a>/Flickr through a Creative Commons license.

A polar bear in the Hudson Bay. Photo Credit Alex Berger/Flickr through a Creative Commons license.

David Iles, a Ph.D. student at Utah State University, expressed some hope for polar bears eating snow geese eggs in a recent story in National Geographic Daily News.

“The nests don’t run away from them like a caribou might,” Iles told Nat Geo. “It’s a ton of calories just basically sitting there that the bears can take advantage of.”

Nevertheless, Iles cautioned that we don’t really know if the bears will take advantage of this bounty.

“We need to do more research to figure out how much benefit this will really be to polar bears, the effects that this will really have on snow goose populations, and how sustainable this type of predation will be, depending on how severe it is,” he told Nat Geo.

But in the same story, Steven Amstrup, chief scientist for Polar Bears International, warned that nothing might replace what polar bears’ current habitat provides them.

“Unfortunately, we have no evidence to suggest that eating geese, or eating char, or eating anything else has any ability to offset the loss of the sea ice and the [primary] foraging opportunities it presents for polar bears,” Amstrup said.

Though Iles is cautiously optimistic about the possibility that polar bears could survive on goose eggs, his recent publication in Polar Biology found that adult geese were an unlikely source of energy for bears (Iles 2013). Other studies have expressed doubt that polar bears could survive by foraging on land at all (Cherry 2013, Derocher 2013).

Northern populations of polar bears may stay in place and continue eating seals, but not the same species. The changes in Arctic temperatures have caused subarctic species of seals to move farther north, and the northern polar bears are now eating them. These seals carry more man-made contaminants, which may affect polar bears (McKinney 2013).

Migrating South Instead of North and Interbreeding with Grizzlies

You might expect that polar bears would move north to find colder climates and sea ice to hunt on — but actually, sea ice drifts south as it breaks up. For this reason, polar bears in some populations are more likely to move south to stay with the ice (Cherry 2013).

Some Hudson Bay population polar bears have already been spotted farther south of their normal territory, leading to an increased number of conflicts between humans and bears (Cherry 2013).

If southern polar bears cannot find a better food source on land, then they will die off as a result of starvation unless humans begin to feed them (Derocher 2013, Stirling 2012).

Furthermore, even if polar bears manage to find food as they move south, they may hybridize with populations of closely related grizzly bears — essentially causing the extinction of a distinct polar bear species (Albrecht 2013).

Possible Next Steps: Reducing Emissions and More Drastic Measures

One possibility: Do nothing, and watch to see if polar bears “sink or swim.” But since climate change is a human-caused problem, doing nothing to mitigate its effects or help affected animals is unpalatable to many (Albrecht 2013).

A polar bear cub at the Detroit Zoo. Photo credit:  <a href="http://www.flickr.com/photos/96223849@N00/85731311/in/photolist-8zoW4-8zoYa-6iJ529-arTgBq-aegg5D-8tnC5z-bpNNPi-azRLtp-azUp5w-azRLuX-azRLy8-azUr8U-azRLAa-azUp4h-azRLrz-azUros-azRLD8-bvuQye-bvuQ6P-bvuRct-bvuSAe-bvuS4F-6kbyQp-2arGrL-8Qv2JG-buvA99-3b4GfE-5ZVzrg-88RHWk-aHMVpP-aFEJoX-as1zLK-aHMpwt-avZ9Lj-3hMDbd-3LogX7-6Jn1A7-9xPfix-4qjpNT-NYWEj-NYWDQ-NYWEh-7ZeVHt-aq8ga3-aq8pdj-5HmbbJ-czfMdm-aH1AvX-dXM7sX-2NVU1-bKH2mc">Dave Hogg</a>/Flickr through a Creative Commons license.

A polar bear cub at the Detroit Zoo. Photo credit: Dave Hogg/Flickr through a Creative Commons license.

One of the most important things that we can do — and that we should do anyway because of all the other impacts climate change will have on people and nature — is to start cutting our carbon emissions, right now. (Find out more about your carbon footprint and how you can reduce it.)

The science says that significant reductions in greenhouse gas emissions alone could be enough to protect northern populations of polar bears indefinitely and to give southern populations a chance of survival (Castro de la Guardia 2013).

But should we not reduce carbon emissions significantly enough to keep polar bear habitat intact, observers have suggested at least three other options for saving polar bears:

+ Polar bear populations could be fed and managed in or near the areas that they currently occupy. This would be costly, but it would keep the bears alive and maintain the tourist industry that has sprung up around these charismatic animals (Derocher 2013).

+ Existing zoos and new specially designed zoos could take in large numbers of polar bears. This option would preserve the species and would provide opportunities for education, but it would be difficult to return the bears to the wild if conditions ever became suitable for them in the distant future (Albrecht 2013, Derocher 2013).

+ People could move polar bears to the Antarctic, where sea ice is expected to remain indefinitely. This would have serious ramifications for Antarctic species like penguins, but if polar bears were located at a distance from penguin colonies and both populations were managed, it could preserve the species as a wild population. We could also move other Arctic species to the Antarctic to increase biodiversity, though such moves may have unforeseen negative effects on the current ecosystem (Albrecht 2013). While this was suggested more as an exercise in making people think about impacts, a smaller scale relocation has been considered (Derocher 2013).

*UPDATE 1/30/14*
I made some corrections to dates and attributions – notably changing Bechsoft 2013 to Bechsoft 2011 wherever it appeared. I also added a note that the Cherry 2013 paper focuses on the Hudson Bay population and a clarification that polar bears could not get all of their calories from terrestrial food sources.
Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.

References

Aars et al. 2013. Variation in detection probability of polar bear maternity dens. Polar Biology, 36: 1089-1096.

Albrecht et al. 2013. The ethics of assisted colonization in the age of anthropogenic climate change. Journal of Agricultural and Environmental Ethics, 26: 827-845.

Bechshoft et al. 2011. Cortisol levels in hair of East Greenland polar bears. Science of the Total Environment, 409: 831-834.

Carrington. 2013. Starved polar bear perished due to record sea-ice melt, says expert. http://www.theguardian.com/environment/2013/aug/06/starved-polar-bear-record-sea-ice-melt

Castro de la Guardia et al. 2013. Future sea ice conditions in Western Hudson Bay and consequences for polar bears in the 21st century. Global Change Biology, 19: 2675–2687.

Cherry et al. 2013. Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics. Journal of Animal Ecology, 82: 912-921.

Derocher et al. 2013. Rapid ecosystem change and polar bear conservation. Conservation Letters, 6: 368-375.

Handwerk. 2013. Watching polar bears eat goose eggs in warmer Arctic. http://news.nationalgeographic.com/news/watching-polar-bears-eat-goose-eggs-in-warmer-arctic/#close-modal

Iles et al. 2013. Terrestrial predation by polar bears: not just a wild goose chase. Polar Biology, 36: 1373-1379.

McKinney et al. Global change effects on the long-term feeding ecology and contaminant exposures of East Greenland polar bears. Global Change Biology, 19: 2360-2372.

Peacock et al. 2013. Population ecology of polar bears in Davis Strait, Canada and Greenland. The Journal of Wildlife Management, 77: 463-476.

Robbins et al. 2012. Maternal condition determines birth date and growth of newborn bear cubs. Journal of Mammalogy, 93: 540-546.

Sonne et al. 2013. Size and density of East Greenland polar bear (Ursus maritimus) skulls: valuable bio-indicators of environmental changes? 34: 290-295.

Stirling and Derocher. 2012. Effects of climate warming on polar bears: a review of the evidence. Global Change Biology, 18: 2694–2706.




Comments: Will Polar Bears Die Out Because of Climate Change?

  •  Comment from Jon Fisher

    While climate change poses a significant threat to polar bears, in some areas hunting them is also a factor in their decline. If you have read some of the arguments from climate change skeptics about polar bear populations increasing, note that a) most populations are in decline, b) there is not very good baseline data on polar bear populations, c) the 1973 restrictions on hunting led to a rebound relative to the levels when they were more heavily hunted, and d) even where populations have increased, declining natality means that the population is expected to decline in the future (see http://rd.springer.com/article/10.1007/s10144-005-0231-2 for details). There is a good overview of this issue at http://www.skepticalscience.com/polar-bears-global-warming.htm

    •  Comment from Lisa Feldkamp

      Thank you for your comment and the links Jon! I focused on the effects of climate for this post, but hunting certainly compounds the problem.

    •  Comment from Larry Harbert

      Hunting has zero detrimental effect on the polar bear,very limited numbers of bears are hunted,and the areas where they are hunted are managed for a sustainable harvest.
      Hunters and hunting are not the enemy of wildlife conservation,we contribute far more in property acquisition money,habitat improvements,labor for habitat improvement,and have done more to re-establish species than any of the animal “rights” groups.
      Hunters brought the wild turkey back from the brink of extinction,along with one group of hunters-Ducks Unlimited-bringing many species of waterfowl back from the brink of extinction,the same for the whitetail deer, elk, and moose,all big game in the U.S is managed for a sustainable harvest by hunters,the funding for the management comes entirely from hunters,through license and tag fees,along with the 11% excise tax on firearms and archery equipment-Pittman-Robertson Act)-the P-R funds provide billions for wildlife conservation.
      The habitat improvements made by hunters/hunters groups/orgs benefit all wildlife,not just whatever species the improvements are designed to help recover.

      Instead of blaming hunters and hunting for species decline,you may want to look at the facts-then you will discover that hunters are doing far more for wildlife conservation than any other group on the planet.

  •  Comment from Glenn Albrecht

    The plight of the polar bear under the pressure of anthropogenic global warming is one that is now a graphic test of the strength of our ethical commitments. Interspecies equity requires that we manage this earth in a way that keeps apex predators like the polar bear in a habitat suitable for them and their prey. If their habitat continues to contract and disappear, then at some point in the future, they too will become extinct. The Albrecht et al (2013)paper was written to encourage us all to contemplate the ethical extreme illustrated by, for example, the very idea of assisted relocation of polar bears to the Antarctic. If assisted relocation seems like an unethical and erroneous idea, then warming the climate such that will change ecosystems all over the world and endanger all species … is an unethical and erroneous idea.

    •  Comment from Lisa Feldkamp

      Thank you for your comment Glen. I think that you put the ethical dilemma very well and I would encourage everyone to read the 2013 paper for a more complete discussion. I agree that warming the climate is unethical and has put mankind into an uncomfortable moral position – we must try to fix the problem, but in doing so, we must avoid creating further disasters for other people and the other species that share our planet. The best path forward at this moment is to stop emitting carbon, but getting that to happen globally will take a Herculean effort. I hope that learning about the plight of polar bears will push people to make that effort.

      •  Comment from Glenn Albrecht

        Yes Lisa, you are spot on. Our paper was all about the need for urgent mitigation so as to avoid the problem of assisted migration/colonisation in the first place. Your article highlights this point very effectively. Like you, I hope that people who read your article will realise that in the face of climate change … we are all polar bears!

  •  Comment from Scott R.O'Connor

    It’s difficult to face species extinctions within our time, particularly if our human impact is a significant, deciding or perhaps sole factor. It becomes more emotional the closer the species resembles us and our kindred species (pets & domestic animals).
    It would be more challenging, no doubt, to raise awareness and action if we were discussing a sea slug two miles deep, or a tiny rodent in an obscure forest at the far flung edges of our world.
    Fact is, the poles of our planet have been without ice before, and without polar bears. There was a time when North America was covered with a glacier a mile deep. This would be far from productive and sustainable for Grasshopper Sparrows and Ivory-billed Woodpeckers, though it did keep the Emerald Leaf Borer at bay (playing with timelines for dramatic purposes, these creatures may not have occupied the same epoch).
    The whole truth is that more species have evolved and become extinct already than exist today. Furthermore, without their extinction this planet would either be overcrowded or inhospitable to humans, miniature-breed dogs and house cats, since there would be predators towering 30 feet outside the door.
    Reality is, we wouldn’t be here in the first place, nor would polar bears, without the natural process of evolution, which includes necessarily in its plan, extinctions.

    Scott R. O’Connor
    Sharon Springs, NY

  •  Comment from Lisa Feldkamp

    Thank you for your comment Scott. It is true that extinctions happen naturally, but there is evidence that the current extinction rate is higher than the “background” or natural extinction rate. See:
    http://www.nature.com/nature/journal/v471/n7336/full/nature09678.html
    http://wwf.panda.org/about_our_earth/biodiversity/biodiversity/
    As you say, the polar bear is just one example and one that appeals to humans (charismatic megafauna). By getting people interested in saving these species and their habitat, we could save other, less charismatic, species that depend on the same habitat.

  •  Comment from chip

    If the sea ice should happen to disappear the seals will still be there but will rest on land rather as they do now on ice.
    I have heard no claim that seals are in jeopardy due to any warming trend.

    •  Comment from Lisa Feldkamp

      Hi Chip, thank you for the comment! I will look into this, I definitely read that some seal populations were moving north, but I didn’t do as much research on seals as on bears.

      •  Comment from Lisa Feldkamp

        Hi Chip, sorry for the delay. Here is an IUCN summary of climate change effects on ringed seals http://cmsdata.iucn.org/downloads/fact_sheet_red_list_ringed_seal.pdf You might also be interested in the McKinney article cited above on the changes in polar bear diet for some discussion of changes to seal populations & more bibliography.

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