New evidence that polar bears survived 1,600 years of ice-free summers in the early Holocene

New evidence indicates that Arctic areas with the thickest ice today probably melted out every year during the summer for about 1,600 years during the early Holocene (ca. 11.3-9.7k years ago), making the Arctic virtually ice-free. As I argue in my new book, this means that polar bears and other Arctic species are capable of surviving extended periods with ice-free summers: otherwise, they would not be alive today.

Money quote: Here we show marine proxy evidence for the disappearance of perennial sea-ice in the southern Lincoln Sea during the Early Holocene, which suggests a widespread transition to seasonal sea-ice in the Arctic Ocean. [Detlef et al. 2023: Abstract]

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Western Hudson Bay polar bears on their way offshore to hunt seals: freeze-up has begun

Official confirmation has come in this morning that polar bears that have spent the summer fasting along Western Hudson Bay now have enough ice to move offshore. That makes this year a bit later than usual (average is 16 November) but is not one of the extremely late freeze-ups, as happened in 1981, 2016 and 2021 when bears didn’t leave until the first week of December (Castro de la Guardia et al. 2017; Miller et al. 2022). Since breakup of sea ice came earlier than usual this summer, this means (as of 30 November) many bears will have been off the ice and without food for 166 days or 5.5 months.

However, so far, there have been no reports from this region of incidents of cannibalism, starving bears found wandering the landscape like zombies, or desperate attacks on people that polar bear specialists have warned us to expect (Abrahms et al. 2023; Stirling and Derocher 2012; Wilder et al. 2017).

Tracking WH Bears

Courtesy Andrew Derocher, University of Alberta, who monitors WH bears:

Close-up of the tracking map below. Note that pregnant females will stay ashore to give birth so not all of these tagged bears are expected to head onto the ice this fall to hunt for seals:

Still not a word from the Polar Bear Alert folks in Churchill, who as of today, haven’t released any of their weekly reports since 23 October 2023.

Ice Conditions in Canada

At 30 November 2023, courtesy Canadian Ice Services shows the expanding band of ice developing along the western shore of Hudson Bay but note also that the rest of the Canadian Arctic, as well as the Beaufort Sea, is completely covered in ice, as is most of Baffin Bay and Foxe Basin:


Abrahms, B., Carter, N.H., Clark-Wolf, T.J., et al. 2023. Climate change as a global amplifier of human–wildlife conflict. Nature Climate Change 13:224-234.

Castro de la Guardia, L., Myers, P.G., Derocher, A.E., Lunn, N.J., Terwisscha van Scheltinga, A.D. 2017. Sea ice cycle in western Hudson Bay, Canada, from a polar bear perspective. Marine Ecology Progress Series 564: 225–233.

Miller, E.N., Lunn, N.J., McGeachy, D., and Derocher, A.E. 2022. Autumn migration phenology of polar bears (Ursus maritimus) in Hudson Bay, Canada. Polar Biology 45:1023-1034.

Stirling, I. and Derocher, A.E. 2012. Effects of climate warming on polar bears: a review of the evidence. Global Change Biology 18(9): 2694–2706.

Wilder, J.M., Vongraven, D., Atwood, T., et al. 2017. Polar bear attacks on humans: implications of a changing climate. Wildlife Society Bulletin 41(3):537-547.

Polar bear sea ice habitat update at 15 November & problem bears in Western Hudson Bay

Abundant polar bear habitat this fall across the Arctic so far, with only Hudson Bay sea ice formation a bit behind schedule. However, Churchill has not seen the anticipated spike in problem bear reports, given the vocal pronouncement by polar bear specialists that it should be experiencing more and more problems with bears when they spent more than 4 months ashore in summer and fall.

News of the most egregious attack by a bear I could find world wide this fall is shown in the video below, filmed 14 November 2023: apparently, the offending bear had spent several days displaying this offending behaviour.

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Walrus and polar bear population size changes in the N. Atlantic over the last 20k years

This is a lesson in how to assess the potential worth of scientific papers. One of two similar Arctic evolution studies got media attention, at least in Canada — about the polar bears, of course — but in my opinion the walrus research conclusions are much better supported, less biased by climate change rhetoric, and lack the hubris present in the polar bear paper.

Both studies use similar sample sizes for the regions they had in common (North Atlantic) and used computer models to determine genetic diversity and population size changes since the LGM. However, the tone of the walrus paper was less emotionally-charged and the caveats of the work were appropriately stated. In my opinion, papers like the polar bear example contribute to eroding the public’s trust in science.

The last Ice Age peaked between about 27,000 and 19,000 years ago. At this time the Arctic was buried under kilometers of glacial ice sheets, and so marine mammals were pushed southwards to areas of ice floes and more open water. Walrus survived in some areas of the Atlantic located further to the south, and as soon as climates warmed again, the ice edge retreated and walrus populations pushed quickly northwards again. This combination of warming and climate-driven dispersal led to local walrus populations becoming more genetically differentiated. Walrus study, Lund University press release 27 September 2023

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Polar Bear Evolution pre-Christmas book sale: discounts on all formats!

I have reduced prices on all formats of my Polar Bear Evolution book for four weeks starting today (8 November-6 December 2023), in time for holiday gift-giving. The ebook version has the largest price reduction (60% of regular price, to US$17.40) but the other discounts are also substantial. This sale is a time limited offer: don’t miss out! Links below.

This is the book for those who are really interested in how grizzly bears could have turned into polar bears and why the story of polar bear evolution could not be told without discussing climate change.

One Amazon reviewer said this about Polar Bear Evolution:

The author of Polar Bear Evolution, Susan Crockford, is a good, credentialed scientist. Her writing is clear; her thinking is also. She has a broad understanding of biology and an informed paleo perspective. Crockford condenses a very large literature on polar bear biology and evolution in this book which will help readers understand the science related to the evolution of an Arctic species. Perhaps the most important aspect of this book is its synthesis of information from the fields of wildlife biology, molecular evolution, paleontology, and climate. Her original ideas and hypotheses on thyroid hormone’s role in evolution are very important and add a credible mechanism of phenotypic change which complements the literature on molecular genetic evolution. Polar Bear Evolution is an important contribution to science and its application in evolutionary biology and wildlife biology. Matthew A. Cronin, Ph.D.

Available at the links below (others also available):



Canada [shipping delay for hardcover version is 4-5 weeks]



Churchill so far has few problems with polar bears despite predictions of a record bad year

Despite misleading warnings in mid-August that a record number of incidents had already taken place, and that Churchill was on track for a record-number of bear problems this fall, the number of incidents and bears captured so far have been well below other years after the same number of weeks ashore. And while this is shaping up to be the longest ice-free season on record for Western Hudson Bay bears, it may not be a record year for problem bears in Churchill.

On average, officers receive around 250 calls from residents and detain around 50 bears every year, according to statistics provided to Live Science by the Manitoba government. The record number of bears captured in a single year was 176, in 2003.” LiveScience, 16 August 2023


Polar bear researchers hiding significant increase in Southern Hudson Bay numbers

Last December, researchers vigorously promoted a possible 27% decline in Western Hudson Bay (WH) polar bear abundance but kept hidden the fact that adjacent Southern Hudson Bay (SH) numbers increased by 30% over the same period.

And surprise, surprise: the bombshell SH results call into question everything the ‘experts’ have been saying about polar bears in Hudson Bay for years.

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Feeding time for Russian polar bears as shorefast ice returns to Laptev Sea, ice-generator of the Arctic

Fall is the second-most important feeding season for polar bears after spring but it comes at different times for different subpopulations. Sea ice formation along shorelines attracts fish and seals and that means polar bears which spent the summer onshore will soon eat again after their summer fast. As usual, the earliest ice formation this year is along the coast of the Laptev Sea, which is one of the primary ‘ice-generators’ of Arctic sea ice. Western and Southern Hudson Bay bears will have longer to wait but the ice will eventually come to them too.

Three adult male polar bears share a seal kill on the newly-formed ice off Wapusk National Park, Western Hudson Bay. 5 November 2020. Buggy cam,

WH photo

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Evolution Earth documentary comments on polar bear survival & adaptation: let’s see how they do

Just a heads-up that this week, PBS in North America will broadcast the “polar” episode of a new documentary called “Evolution Earth.” In my area, it’s scheduled for Wednesday, September 27 at 10:00 PM. It remains to be seen whether this is really about evolution or (given those involved in its production) simply more climate change propaganda similar to that promoted by Attenborough, but I intend to watch and report back.

About the Show: “Evolution Earth embarks on a global expedition to reveal the animals keeping pace with a planet changing at superspeed. Heading out across the globe to distant wilds and modern urban environments, five episodes track how animals are moving, using ingenuity to adapt their behavior, and even evolving in unexpected ways.

We follow heart-warming tales of resilience that redefine our understanding of evolution, and hint at how nature can show us a path towards a sustainable future for Planet Earth. The series is narrated by Dr. Shane Campbell-Staton, who guides us through each episode in an intimate narrative style, drawing on his background as an evolutionary biologist.”

Episode 4 | IceAt the planet’s frozen extremes, shifts in animal movement and behavior reveal vital information about our future world. Examine polar bears in the Arctic, penguins in Antarctica and other animals surviving in icy worlds.

Find tips for watching outside the US here.

UPDATE 27 September 2023: Well, as I expected, this show was full of Attenborough-style nonsense about starving polar bears waiting for sea ice to form along Western Hudson Bay, the bears presented as “canaries in a coal mine” indicators of climate change, with an activist scientist saying she’s “pissed” about climate change. They used charts of the very distinctive pattern of sea ice formation that took place in November 2020 to illustrate how freeze-up was “later and later each year” even though 2020 was one of the earliest freeze-ups on record (bears were successfully hunting from shorefast ice as early as 30 October). A waste of 15 minutes: I couldn’t bear to watch what they did with the penguins.

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17 years of near-zero trend in September sea ice demolishes claim that more CO2 means less sea ice

If the hottest year ever can’t precipitate ‘ice-free’ conditions in September, what’s it going to take? Arctic sea ice failed to nose-dive again this year, undoubtedly disappointing expects who have been anticipating a ‘death-spiral’ decline for ages. Arctic sea ice hit its seasonal low sometime around mid-September this year and although the precise value hasn’t been published, the average September ice coverage will likely be about 4.2 mkm2 once it gets announced in early October.

This means we have now had 17 years of a near-zero trend for September sea ice, extending the nearly-flat trend NSIDC sea ice experts acknowledged four years ago. This surely busts a huge hole in the prevailing concept that more atmospheric CO2 causes less summer sea ice. Note that CO2 levels measured in August 2023 were 419.7 parts per million (ppm), compared to 382.2 in August 2007, a rise of 37.5ppm with no corresponding decline in summer sea ice (and vs. 314.2 ppm in 1960). Measured in metric tons, CO2 emissions due to fossil fuels rose from 31.1 billion in 2007 to 37.1 billion in 2021 (last year of data), again with no corresponding decline in summer sea ice.

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New study that claims it can directly link GHG emissions to polar bear cub survival is poppycock

A global warming miracle has happened. While no scientist worldwide has ever drawn a straight line between greenhouse gas emissions and population declines in a species considered at risk due to climate change, a new paper just published in Science Magazine claims to have performed this unlikely feat for polar bears. It’s called “Unlock the Endangered Species Act to address GHG emissions.”

Note this analysis has not been peer reviewed: as a “Policy Forum” contribution, it’s considered by the journal to be a public interest commentary, not a research paper.

One might be forgiven for asking whether this work represents solid, reproducible science or simply well-timed, sciency-looking rhetoric ready-made for the litigious Center for Biological Diversity to pressure the US government to increase protections for polar bears before the 2024 US election. It is surely no coincidence that this paper made its appearance near the seasonal low for Arctic sea ice as well as during the 15-year anniversary of the ESA listing of polar bears as ‘threatened’ and the 50th anniversary of the ESA itself.

Moreover, knowing this paper was in the pipeline might explain why the 2022 government report on the most recent Western Hudson Bay polar bear decline, which I discussed yesterday, has been kept secret for so long: the results of that report are cited in this new Science paper as supporting evidence that sea ice declines are responsible for recent population declines, which Reuters said in December was clearly not the case for the period 2017-2021.

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