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Today I saw this image comparing a polar bear from 2009 to one from 2019:

polar bear in 2009 vs 2019

It’s been shared nearly 50k times, as of writing this.

My question is is this accurate? My main suspicions are the following:

  1. 2019 has only just begun. It seems a little unlikely that the image of the polar bear was taken in the last 15 days (but not impossible, of course)

  2. The second polar bear appears to have just emerged from water (drops coming from its tail?). This can often cause fur to clump (it happens to my dog when he is bathed). Is this causing a lot of the difference?

  3. Were the images taken at different times of year? I believe that polar bears hibernate. It could be that the first polar bear has been eating, storing up fat for the winter period, and the second has just left hibernation.

  4. Is the image of the same polar bear? I’m fairly confident it isn’t - hence I’ve taken it to be a comparison of the typical bear then and now.

closed as off-topic by DevSolar, Sklivvz Jan 16 at 21:13

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I am aware that it may be difficult to find much evidence around these photos.

They are, actually, irrelevant to the question as summarized by you on request. The pictures are meant to be illustrative; criticising the second picture for e.g. giving the "wrong" year is attacking a straw man.

(For completeness, I am addressing your questions about the picture at the end of this answer, anyway.)


It would be interesting to know if the average weight of polar bears has reduced in the last 10 years

Yes.

From Wikipedia: Polar bears # Climate change, emphasis mine:

The effects of climate change are most profound in the southern part of the polar bear's range, and this is indeed where significant degradation of local populations has been observed.[182] The Western Hudson Bay subpopulation, in a southern part of the range, also happens to be one of the best-studied polar bear subpopulations. [...]

Due to warming air temperatures, ice-floe breakup in western Hudson Bay is currently occurring three weeks earlier than it did 30 years ago, reducing the duration of the polar bear feeding season.[163] The body condition of polar bears has declined during this period; the average weight of lone (and likely pregnant) female polar bears was approximately 290 kg (640 lb) in 1980 and 230 kg (510 lb) in 2004.[163]

Source [182] is:

  • Arctic Climate Impact Assessment (2004). Impact of a Warming Arctic: Arctic Impact Climate Assessment: Key Finding 4. Cambridge: Cambridge University Press. ISBN 978-0-521-61778-9. OCLC 56942125..

Source [163] is:

  • Stirling, Ian; Derocher, Andrew E. (2007). "Melting under pressure: The real scoop on climate warming and polar bears" (PDF). The Wildlife Professional (published Fall 2007). 1 (3): 24–27, 43.

I don't think there is reason to believe that this is offset by an increase of 20% in body weight in other regions (lacking any plausible increase in living conditions).


As for your questions about the image in particular:

2019 has only just begun. It seems a little unlikely that the image of the polar bear was taken in the last 15 days (but not impossible, of course)

It was not taken 2019, but in 2015. The idea of the "2019" / "2009" given in the picture is not, however, to claim that those were the years in which the pictures were taken. As stated in the FB post ("The 10 years challenge we should really care about..."), the idea was to illustrate the worsening situation of polar bears (and probably climate change in general), *in context of the "10 year challenge". The "2019" is today, the "better" 2009 (to illustrate that the situation is worsening) is just "10 years back from right now".

The second polar bear appears to have just emerged from water (drops coming from its tail?). This can often cause fur to clump (it happens to my dog when he is bathed). Is this causing a lot of the difference?

An image search for "wet polar bear" shows a wide range of results, with the specimen pictured under "2019" definitely being on the emaciated side. Yes, wet fur makes a difference -- but not that much.

Were the images taken at different times of year? I believe that polar bears hibernate. It could be that the first polar bear has been eating, storing up fat for the winter period, and the second has just left hibernation.

Polar bears are not true hibernators. But even a healthy female bear just out of "hibernation", being wet does not look like the specimen in the "2019" picture.

Is the image of the same polar bear? I’m fairly confident it isn’t - hence I’ve taken it to be a comparison of the typical bear then and now.

It's nowhere claimed that it's the same bear. The life expectancy of a wild polar bear rarely exceeds 20 years.

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    Technically, in context of the ten-year challenge, the questions that the OP is asking are the actual claims. The ten-year challenge says "In that year, I looked like that. In this year, I look like this." Saying "but of course that's rhetorical. They don't actually mean that." is, in effect, saying "They're lying, but they're not trying very hard, and you'd have to be dumb to not realize it." As far as reasonable arguments to bring forth on Skeptics, that's effectively a particularly insulting form of notability challenge. – Ben Barden Jan 16 at 20:53
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    I find it implausible that the person who put “2009” and “2019” on this image did not intend it to imply that 10 years had passed between each photo, and that the photos were taken in their respective years. Perhaps that interpretation was not their intention, but, if that is the case, it’s a very foolish thing to add to the image. I, personally, interpreted as I listed above, and would make an educated guess that a significant portion of the 50k people who shared it would hold the same impression. – Tim Jan 16 at 20:55
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    @Tim: So you removed the only relevant portion of the question and reduced it to a pure straw man. Assuming bad faith (and quite some stupidity) by the poster instead of the 10YearChallenge context made explicit on FaceBook. Well done.</sarcasm> – DevSolar Jan 17 at 7:50
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    @DevSolar you know what Dev, I have complained when my food didn’t look good enough. That’s not an absurd thing to do... – Tim Jan 17 at 8:03
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    @Tim: That wasn't the question, and if you do not realize the dishonesty behind your question-as-asked, I can't help you. But you can't make me agree with you, fortunately. – DevSolar Jan 17 at 8:05

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