‘Stress’ is shrinking polar bears

Polar bear tongue

The BBC reports:

Polar bears have shrunk over the last century, according to research.

Scientists compared bear skulls from the early 20th Century with those from the latter half of the century.

Their study, in the Journal of Zoology, describes changes in size and shape that could be linked an increase in pollution and the reduction in sea ice.

Physical “stress” caused by pollutants in the bears’ bodies, and the increased effort needed to find food, could limit the animals’ growth, the team said.

Okay, it’s not most important climate story in the world, but it does let me use the above photo again.  I should note that the NYT‘s Revkin blogged last month, “More Polar Bear Populations in Decline“:

There is rising concern among  polar bear biologists that the big recent summertime retreats of sea ice in the Arctic are already harming some populations of these seal-hunting predators. That was one conclusion of the  Polar Bear Specialist Group, a network of bear experts who  met last week in Copenhagen to review the latest data (and data gaps) on the 19 discrete populations of polar bears around the Arctic. The group, part of the  International Union for Conservation of Nature, includes biologists in academia and government and at nonprofit conservation organizations. Only one bear population is increasing (in the Canadian high Arctic), while eight are declining in numbers, the scientists said. At its last meeting, in 2005, the group concluded that five populations were in decline. Three populations appear to be stable and seven are too poorly monitored to gauge a trend.

As for the new study, here’s the abstract for “Craniometric characteristics of polar bear skulls from two periods with contrasting levels of industrial pollution and sea ice extent” (subs. req’d):

A morphometric study was conducted on six skull traits and seven teeth traits of 282 polar bear Ursus maritimus skulls sampled in East Greenland from 1892 to 2002, the polar bear material originated from two distinct periods: one period covering 1892-1939 and the other from 1961-2002. The first period being before the introduction of organochlorines in the Arctic environment and having more extensive sea ice cover when compared with the later period. Admixture analysis, followed by multivariate analyses provided evidence for morphometric differences in both the size and the shape of individual skulls collected in the two periods. These findings are possibly a consequence of environmental factors, such as exposure of organohalogens and changed extension of sea ice, ultimately affecting the amount of prey available, a general weakening of the immune system and reduced reproductive success, factors that can affect the individual growth and the realized size at maturity. The process of reduced reproductive success due to a high concentration of organochlorine and/or changes in the amount of food resources may also have affected the polar bears’ genetic composition and effective population size. Changes in the genetic composition of the population are suggested to have contributed to the observed morphometric changes with time. The fact that environmental and genetic changes produce different combinations of patterns of morphometric changes allows us to individuate the causes of the morphometrical modifications.

In plain English:

“Because the ice is melting, the bears have to use much more energy to hunt their prey,” explained Cino Pertoldi, professor of biology from Aarhus University and the Polish Academy of Science, and lead scientist in this study.

“Imagine you have two twins – one is well fed during its growth and one is starving. (The starving) one will be much smaller, because it will not have enough energy to allocate to growth.”

The team, which included colleagues from Aarhus University’s Department of Arctic Environment, also found shape differences between the skulls from the different periods.

This development was slightly more mysterious, said Dr Pertoldi.

He explained that it was not possible to determine the cause, but that the changes could be linked to the environment – more specifically to pollutants that have built up in the Arctic, and in the polar bears’ bodies.

The aim of the study was to compare two groups of animals that lived during periods when sea ice extent and pollution levels were very different.

The pollutants that the scientists focused on were compounds containing carbon and halogens – fluorine, chlorine, bromine or iodine.

Some of these compounds have already been phased out, but many still have important uses in industry. These include solvents, pesticides, refrigerants, adhesives and coatings….

Rune Dietz from Aarhus University was another member of the research team.

He explained that he and his colleagues had already determined a link between man-made “persistent organic pollutants” and reduced bone mineral density in polar bears – which could leave the animals vulnerable to injury and to the bone disease osteoporosis….

He said: “Polar bears are one of the most polluted mammals on the globe.”

And you thought Homo “sapiens” sapiens had nothing in common with Ursus maritimus.

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23 Responses to ‘Stress’ is shrinking polar bears

  1. Jeff Huggins says:

    I think stress is shrinking me, too!

    (and it probably shows in some of my comments)

    So, I’ll just add one quick positive point. As it turns out, other things being equal, humans feel better — less stressed — when they feel they have at least a reasonable and fair degree of “control” over their situations, i.e., when they feel that their actions matter.

    That’s why, as difficult as this all is, we will feel better when we become more active and activated (in civil ways of course), for example, when we’re out there helping Bill and the rest of the 350 folks.

    Indeed, one of the best ways to get less stressed yourself is to get out and help the over-stressed Polar Bears. No joke.



  2. Hey Skipper says:

    How many bears are there, compared with a century ago?

  3. ecostew says:

    Hey Skipper – they are loosing their habitat!

  4. Michelangelo says:

    yeah, yeah, the Economist had a similar story —

    Anyways you should probably check out this post… great rating for the “relevance” and “logic nature” of climate change-ish points —

  5. Mike Strong says:

    the blog with very few viewers….sigh Joe…nobody is listening to you. Time to get a job as a reception guy at a hotel in D.C.

    You are failing.

    [JR: Huh? You don’t know much about blogs, do you? If there is another climate blog in the world that has as many subscribers, they have chosen to keep it a secret. Yes, I do lose some commenters (and visits and page views) with the feed and with letting so many other websites, like Grist, repost my stuff. But I’ll take the commenters I do have over just about anyone else’s.]

  6. Roger says:

    Jeff says that people feel better when they have some control, i.e., by helping to be part of the solution, not part of the problem. That’s why the climate movement is gaining momentum, as citizens become more aware of the benefits of taking action to slow climate change, and the dire consequences of inaction. Check out re October 24th!

  7. Chris Winter says:

    Mike Strong, I suggest you keep an eye on this blog’s RSS tally.

  8. (Bjorn) Lomborg will declare that this is a good thing.

    Pielke (pick one) will deny that it is happening after admitting to all of the facts.

    Will will sputter incoherently and try to turn it into a comment about baseball.

    Krauthammer will demand we commence immediate regime change (Look! The Bear is sticking its commie/islamofascist tongue out at us!)

    Watt will point to irrelevant data sets and demand that we stop posting.

    Who have I missed?

  9. Mike Strong says:

    Non starter Chris Winter. This blog fails. I saw the numbers. My son got more viewers for his Spongebob video. I don’t lie to myself. Neither should you.

  10. DG says:

    Mike Strong, I’d like to point out that most CP readers might not feel the need to comment on every post. I’ve posted maybe three comments (including this one) on the hundreds of blog posts I’ve read since discovering the site months ago. I think it doesn’t need explaining why some blogs draw more comments than others, and it’s definitely not a reflection of readership or how well an author is conveying her or his message.

  11. paulm says:

    The MSM is starting to get it. Especially the magazines. But also its seeping in to the dailies. This since August.

    The cascade of climate change events is forcing the topic to the forefront of the main news. Usually if they covered CC they would tuck it away in the science section, which was not good enough….

    Climate change doubles tundra plant life, boosting shrubs, grasses

    A Real Fish Story

    Canada considers adopting U.S. Beaufort Sea fishing moratorium
    Impact of climate change prompts ban pending more research

    Where have all the salmon gone?
    And where on Earth are our public watchdogs? Scientists tipped them to this tragedy in 2007

    Iceberg Melts Right Before Rick Sanchez’s Eyes(CNN)

    After national park tour, Udall, McCain agree global warming a problem,0,6162897.story

    The psychology of climate change

  12. Al says:

    I’ve occasionally seen comments to the effect that a few should be let loose in the Antarctic, and no indication that it would be a retrograde step. Can’t some mating pairs just be dropped off near a penguin or seal colony and see how they go? Why hasn’t it been done?

  13. Hey Skipper says:

    Why is my comment still in moderation?

    [JR: They don’t all make it thru. You need to do better than the wild speculation when criticizing a peer-reviewed study.]

  14. Mike#22 says:

    Pat Michaels will write a book explaining that since he is State Climatologist for Life, we should not become confused by actual science, especially polar bear studies.

    The Hearland Institute will host a conference on why sunspot cycles determine polar bear weight, and polar bears where bigger back then because they had to swim across the northwest passgage all the time.

    API plans it’s next set of “grassroots” events with slogans like “Drill the Arctic” and “Move over Polar Bears”

  15. Sable says:

    moving some “breeding pairs” to Antarctica = bad idea. Introducing a predator to a place where it is not normally found is rarely, if ever, a good idea.

    Penguin populations are already stressed and declining because of global warming (and probably other, ultimately human generated factors). None of the animals down there have evolved with, or are adapted to, a top predator which can easily move on land and sea. With the exception of the extinct Great Auk, sea birds in the arctic which have a similar ecological role as penguins are all capable of flight and choose less accessible breeding locations. This is likely a response to the presence in the arctic regions of land based mammalian predators.

    Penguins breeding colonies on land would be very vulnerable as the bears moved in for the buffet. The main animal threats penguins deal with on land are other birds – e.g. skuas and giant petrels. Near shore they have to contend with leopard seals.

    Besides, with Antarctica warming and melting too, any such “solution” would be relatively short lived.

  16. Richard L says:


    I read your excellent blog probably twice per day. I rarely leave a comment because I am learning so much from your postings. I feel if I have something to contribute, or a strong opinion, I do comment.

    It seems strange to me to rate a blog by number of comments. I would think that few readers want to read a comment from me that says ‘right on!’

    To you, does the definition of a blog ‘success’ include comments from readers? If not, how do people like me show our ‘participation’ by reading your blog?

  17. Dano says:

    How many bears are there, compared with a century ago?

    Give the date of the hunting ban and we’ll talk.

    Oh, wait: spamming comments on sites that negate your ideology isn’t ‘talking’. Never mind.



  18. Mutmansky says:

    I wanted to third DG’s and Richard L’s comments. I’ve been reading CP for several months (maybe a year now?), and while I usually hit CP every day, I usually don’t have anything additional to contribute that hasn’t already been stated by one of the more regular commenters. In fact, I think this might be my second comment ever. Same for RealClimate. I hit that one regularly as well, but I don’t think I’ve ever commented.

    I think there’s probably a lot of people in this category and I think there’s two reasons for it:

    1. Wisdom is knowing that you don’t know that much.
    2. Better to keep your mouth shut and let people think you are a horse’s behind, then to open your mouth and remove all doubt.

    So from a long time reader and infrequent commenter, keep up the good work Joe!

    [JR: Thanks. I get about 100 comments a day (less during the summer). Clearly, a lot of my readers have migrated over to the feed, and never bother coming to the site, which hurts my stats. But fundamentally, when you post 5 or 6 times a day, you’re going to end up with fewer comments on most posts — especially if you refuse to publish long-debunked disinformation from deniers. Compare the amount of comments here to Grist or Wonk Room — both of whom I think get more visits — and you’ll see that I still do pretty darn well. I greatly appreciate the commenters here, and I know the people who do comment here appreciate the fact that this isn’t an unmoderated mess like most newspaper blogs.]

  19. Bob Wallace says:

    Climate change shrinks sheep. But it’s not stress, but somewhat the opposite.

    Warmer winters mean that smaller wild sheep have greater chance of survival on a remote Scottish island. Smaller sheep are not being removed from the gene pool.

    Climate change won’t mean all bad, everywhere, all the time. (Unless you’ve got a thing for large sheep.) Some places may benefit from better environments, at least for a while.

    Down the road all the sheep on that isle may be in deep trouble if climate change either causes lack of rainfall or rising temperatures to wipe out their food source. Or causes the Gulf Stream to shut down, freezing them out.

    Or maybe environmental refugees will flee there and eat them all….

  20. Jenny says:

    “Only one bear population is increasing (in the Canadian high Arctic), while eight are declining in numbers, the scientists said.”

    The single increasing polar bear population is one that was severely over-hunted previously.

  21. Jenny says:

    Re Bob Wallace & “shrinking” animals:

    It could be a valid point that — in addition to suffering the effects of food-deprivation and chemical contamination — polar bears might be “shrinking” due to warming Arctic temperatures. The low surface area to volume ratio of a big fat polar bear body favors heat retention, which of course is essential for life in a frigid Arctic habitat. Conversely, as the Arctic warms, a smaller body size might evolve to prevent over-heating. But at the rate the Arctic is being transformed by climate change, polar bears aren’t going to survive long enough to evolve bodies that are smaller than they are now (or bodies that can survive without sea ice).

  22. Bob Wallace says:

    We’ve learned that evolution can happen quite rapidly. It’s not necessarily the slow, plodding process that we once imagined it.

    Perhaps polar bears will shrink along with the polar ice cap, perhaps they will morph to a land based animal. Or, unfortunately, they might fail to adapt and disappear.

    The chance that polar bears might find an ecological niche in a changing world is not to excuse our damage of their environment. It’s just an observation on how things don’t follow a single, simple path.

    It’s like the observation that we can observe cooling in a few parts of the globe while the rest dangerously heats and why we can observe a buildup of the snow pack on Mount Shasta while the snow pack of the nearby, and much greater Sierra Mountains declines.

  23. Jenny says:

    Absolutely right, Bob. One more observation re polar bears and the ecological complexity of a world altered by climate change: For a variety of reasons, I think it’s far more likely that brown bears will expand their range northward(they already are doing so), and out-compete polar bears for the newly warmed ecological niches in most Arctic regions, than that polar bears will evolve quickly to become successful land-based animals.