Arctic sea ice is constantly changing which means polar bears must be flexible in their requirements

In honour of upcoming ‘Arctic Sea Ice Day’ (15 July), I revisit my 2015 essay on sea ice stability and polar bears, called The Arctic Fallacy. It challenges the flawed and out-dated ecological concept that under natural conditions, sea ice provides a stable and predictable habitat for polar bears, walrus and seals. The wide-spread adoption of this fallacy has allowed the present-day doom and gloom attitude of most Arctic specialists to develop.

[Polar Bears International have declared July 15 to be ‘Arctic Sea Ice Day’ to further its propaganda efforts to ‘save our sea ice’, which they claim is disappearing at an alarming rate due to global warming.]

We know that sea ice changes from season to season. However, the concept that sea ice is a stable habitat assumes that these seasonal changes are predictable and virtually the same from one year to the next under natural conditions – at least, similar enough that the differences cannot be responsible for marked declines in population size (see also Crockford 2019).

As I explain in my essay, biologists were taught at university that sea ice should be a stable habitat and as a result, they’ve glossed over evidence they collected to the contrary. See recent posts here, here and here, for example. In addition, we have the evidence from the Barents Sea that most female polar bears are flexible enough to have shifted to the Franz Josef Land archipelago or its adjacent mobile pack ice for making maternity dens when sea ice around the eastern Svalbard archipelago dropped below critical levels: they didn’t stay and lose their cubs, they simply moved east a little bit where conditions were better (Anderson et al. 2012; Aars et al. 2017).

The big media item from last month about a population of bears living in fjords free of land-fast ice for much of the year in Southeast Greenland is additional evidence that polar bears are flexible in their sea ice requirements (Laidre et al. 2022). In recent years, some polar bears also appear to be shifting from the western Beaufort Sea into the Chukchi Sea, where food has become particularly abundant due to reduced summer sea ice (Frey et al. 2021; Rode et al. 2014, 2018)

Not only has this behavioural flexibility of polar bears been disregarded but the known negative effects on populations of short-term natural variations in sea ice and snow cover over sea ice have been entirely ignored in modeled predictions of future conditions. These are two of the main reasons computer models of polar bear survival have failed in the past and will continue to fail going forward.

Read the summary of my 2015 essay below and download the entire paper here.

Citation: Crockford, S.J. 2015. The Arctic Fallacy: Sea ice stability and the polar bear. Briefing Paper #16, Global Warming Policy Foundation, London. PDF.

The Arctic Fallacy: Sea Ice Stability and the Polar Bear

Since the late 1960s, Arctic marine mammal conservation has been based on the assumption that sea ice provides a stable, predictable environment for polar bears and Arctic seals: today, it underpins their ‘threatened with extinction’ status. A stable environment, the oversimplified K-selection theory goes, should support populations at relatively high levels over time, without marked variation in size due to habitat change.

This idealized concept was strongly promoted by the most popular university-level ecology textbooks of the 1970s and was embraced by early polar bear biologists, who began their careers at a time when polar bear were truly threatened with extinction by overhunting.

Observations since then, however, have shown the assumption of sea ice as a stable habitat over short time scales is false. Spring sea ice thickness has been naturally variable over time scales of a few years to decades in the Beaufort Sea, East Greenland, and Hudson Bay; spring ice extent has been naturally variable in the Barents Sea for centuries and spring snow depth on sea ice is known to vary over short periods.

Marked declines in polar bear and ringed seal survival in response to thick spring sea ice and reduced snow depth have been documented. These two variables are closely tied because spring (April — June) is the period of on-ice birth and nursing for ice-dependent seals and is also when polar bears consume two-thirds of their annual prey.

Apparently expecting stable or increasing populations, despite their own evidence to the contrary, Arctic biologists now surprisingly attribute virtually every downturn in population size of Arctic species to declines in summer sea ice blamed on human use of fossil fuels.

Regardless of such willful blindness to the facts, the assumption that Arctic sea ice is a naturally stable habitat over short time frames is a biological fallacy. Predictive population models based on this myth are flawed, their results illusory. Yet, the International Union for the Conservation of Nature (IUCN) and the US government have, for the first time, accepted modeled (future) population declines of Arctic species based on modeled (future) summer sea ice changes as valid threats to their survival, all built upon this fallacy.

From the foreword by geneticist Matthew Cronin:

Scientists know that the assumptions used in a model are critical to its validity. For example, assumptions in genetic models that I use (e.g., mutation rates or species divergence times) are estimates, not known quantities, making model results uncertain. It is legitimate to use models with uncertain assumptions, but the uncertainty of the model results must be openly acknowledged and alternatives considered. Crockford demonstrates that this has not been done for polar bears and that the basic assumption of stable sea ice is not valid.  She strengthens her argument with revelations that there is a consensus that winter sea ice is expected to persist despite global warming, and that heavy spring ice, not absence of summer ice, has a negative impact on seals and thus polar bears.  These points could change the entire argument about the future survival of polar bears. 

The constant chorus declaring crises for high-profile wildlife (snail darters, spotted owls, wolves, bears, etc.) has led to what I call the “pan-impact” paradigm: there is always a human impact on wildlife, and scientific information will be found to support a preconceived conclusion. This has resulted in many of us now having a skeptical “boy who cried wolf” attitude regarding wildlife: everything people do will be claimed to have a negative impact on some critical species, and must be corrected by top down government regulation (of which the ESA is a preferred mechanism in the U.S.). This is dangerous, not only to science and economics, but because we might not pay attention when real threats arise.

I appreciate that global warming is potentially very important. However, we should not stifle open discussion and debate that is integral to science. Crockford’s article is a valuable contribution to the scientific discourse on polar bears, and I hope it gets a fair hearing.  I encourage readers on both sides of the climate debate to engage in civil discourse on these issues, and not prejudge any work without thoughtful consideration. 


Aars, J., Marques,T.A, Lone, K., Anderson, M., Wiig, Ø., Fløystad, I.M.B., Hagen, S.B. and Buckland, S.T. 2017. The number and distribution of polar bears in the western Barents Sea. Polar Research 36:1. 1374125. doi:10.1080/17518369.2017.1374125

Andersen, M., Derocher, A.E., Wiig, Ø. and Aars, J. 2012. Polar bear (Ursus maritimus) maternity den distribution in Svalbard, Norway. Polar Biology 35:499-508.

Crockford, S.J. 2019. The Polar Bear Catastrophe That Never Happened. Global Warming Policy Foundation, London. Available in paperback and ebook formats.

Frey, K.E., Comiso, J.C., Cooper, L.W., Grebmeier, J.M. and Stock, L.V. 2021. Arctic Ocean primary productivity: the response of marine algae to climate warming and sea ice decline. 2021 NOAA Arctic Report Card, DOI: 10.25923/kxhb-dw16

Laidre, K.L., Supple, M.A., Born, E.W., et al. 2022. Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st century sea-ice conditions. Science 376(6599):1333-1338.

Rode, K.D., Regehr, E.V., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2014. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Global Change Biology 20(1):76-88.

Rode, K. D., R. R. Wilson, D. C. Douglas, V. Muhlenbruch, T.C. Atwood, E. V. Regehr, E.S. Richardson, N.W. Pilfold, A.E. Derocher, G.M Durner, I. Stirling, S.C. Amstrup, M. S. Martin, A.M. Pagano, and K. Simac. 2018. Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity. Global Change Biology

via polarbearscience

July 14, 2022 at 12:35AM

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