How will global warming affect polar bears?
What the science says...
Polar bears are in danger of extinction as well as many other species.
Climate Myth...
Polar bear numbers are increasing
“A leading Canadian authority on polar bears, Mitch Taylor, said: ‘We’re seeing an increase in bears that’s really unprecedented, and in places where we’re seeing a decrease in the population it’s from hunting, not from climate change.'” (Scotsman.com)
At a glance
Ursus maritimus. The Latin name for the world's largest bear hints at its high dependence on the seas around the Arctic. Polar bears are an apex predator that depend on seals for their food. Because of that dependence they mostly live and hunt out on the sea-ice. Excellent swimmers, they are equipped with the means to swim in the frigid Arctic waters. Thick body fat and a heavy, water-repellent coat make such a lifestyle feasible.
Polar bears live in 19 distinct groups around the Arctic. We don't have great data on eight of the groups. Arctic fieldwork is fraught with logistical problems, especially out on the sea-ice. Regarding the other groups, as of 2017, five are regarded as stable. Two are increasing whereas four are declining. Therefore, it's a mixed picture.
The reason why the picture is mixed lies in the four distinct eco-regions making up the Arctic. Let's look at these. Firstly there is the Seasonal Ice Ecoregion off Canada. Here, the ice has always melted in the summer. The bears hunt voraciously before that happens and then go through a seasonal fast on land. Unfortunately, because the ice-melt is beginning earlier and ending later, the fast period is getting longer, causing malnutrition and cub mortality. This bear population is the one that is definitely declining.
Stretching from Alaska to Svalbard is the Divergent Ice Ecoregion. Here, the ocean currents constantly move the sea-ice offshore as it forms. In summer, new ice does not form and a wide gap of open water exists between sea-ice and the land. Offshore, the sea ice is over the depths of the Arctic ocean - an area of relatively low food productivity. The seals remain near land, in the more productive shallows. Again, the problem facing the bears is the increased length of the ice-free season, for the same reasons as above. Bears living in this region are particularly vulnerable.
In the Convergent Ice Ecoregion, from the North Barents Sea around to Eastern Greenland, ice collects along the shore. The bears living in this region therefore have constant access to ice over shallow productive seas. Finally, there is the Archipelago Ecoregion, around the islands of the Canadian Arctic. Here too, the polar bears have been able to remain on the ice all year round. Both Ecoregions are therefore a known or potential stronghold for them.
The primary threat to all of these regions is obviously sea-ice loss due to climate change. As the sea-ice retreats, the bears have to spend more time on land. This can bring them into contact with human populations and such encounters tend not to end well.
Polar bears belong on the sea-ice. The long term trend for sea-ice extent is downward. Even if some populations are stable or even increasing, it's an uneven picture due to the differing characteristics of the regions they inhabit. Rapid Arctic climate change - Arctic Amplification as it's known - is real. Concern for this magnificent creature is entirely justified.
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Further details
Polar bears are found in the Arctic circle and surrounding land masses. There are 19 recognised subpopulations, and estimates place their numbers at about 20,000 to 25,000. Polar bears are classed as vulnerable by the World Conservation Union (IUCN) and listed as a threatened species under the US Endangered Species Act. Yet some claim that polar bear numbers have increased since the 1950s and are now stable. So what is the situation for this species?
First of all, a few points need to be made about polar bear numbers:
- Nobody really knows how many bears there were in the 1950s and 1960s. Estimates then were based on anecdotal evidence provided by hunters or explorers and not by scientific surveys.
- Polar bears are affected by several factors on top of climate change, including hunting, pollution and oil extraction. The introduction of snowmobiles, aeroplanes and ice breakers and the increased hunting that followed led to a decline in certain populations.
- On the other hand, the International Agreement on the Conservation of Polar Bears was introduced in 1973. That restricted or even banned hunting in some circumstances, resulting in a recovery of polar bear numbers.
- Not all subpopulations are affected to the same degree by climate change. While some subpopulations are well studied, others are data-poor. That means there is insufficient information to make specific statements about current and past numbers.
With this caveat in mind, what do the figures actually say? According to a 2019 report by the World Wildlife Fund, of the 19 recognised subpopulations of polar bears, four are in decline, two are increasing, five are stable and eight don’t have enough data to draw any conclusions (fig. 1).
Figure 1: Population status of polar bears around the Arctic as of 2021. Data: Arctic Portal. Map: Wikipedia. Key to eco-regions, clockwise from bottom: EG = East Greenland; DS = Davis Strat; BB = Baffin Bay; KB = Kane Bay; SHB = Southern Hudson Bay; WHB = Western Hudson Bay; FB = Foxe Basin; GB = Gulf of Boothia; QE = Queen Elizabeth; NW = Norwegian Bay; LS = Lancaster Sound; VM = Viscount Melville Sound; MC = M'Clintock Channel; NBS = Northern Beaufort Sea; SBS = Southern Beaufort Sea; CS = Chukchi Sea; LVS = Laptev Sea; KS = Kara Sea; BS = Barents Sea.
Both habitat degradation and over-harvesting are responsible for the decline in some populations. To understand why the IUCN and US Endangered Species Act consider polar bears to be at risk, it is important to look at how rising temperatures are likely to affect their habitat in the future. Polar bears are highly specialised mammals which rely heavily on sea ice for food and other aspects of their life cycle. Satellite data show that Arctic sea ice has been decreasing for the past 30 years. Projections show that this trend will only continue as temperatures carry on rising. The changes in sea ice affect polar bears in several ways:
- The early retreat of summer sea ice means that bears have less time to hunt and therefore less time to build up fat reserves.
- The fragmentation and reduction in sea ice has several impacts. It forces the bears to swim longer distances, using up some of their fat reserves. It also reduces the number of seals, which are the bears’ main source of food, and impedes travelling and den making. And it also forces the bears to spend more time on land, with increased interactions with humans potentially leading to higher mortality.
To get an idea of the potential impacts of future climate change on polar bears, we can look at subpopulations found at the bears’ southern range, where habitat changes have been most noticeable so far. A good example is the western Hudson Bay subpopulation, which is one of the best studied. Here, ice floe break-up is taking place earlier than 30 years ago, effectively reducing the feeding period by about three weeks. As a result, the average weight of female polar bears dropped by about 21% between 1980 and 2004, and the population declined by 22% between 1987 and 2004. In Alaska, there is evidence of increased cub mortality caused by a decline in sea ice.
In conclusion, the reason polar bears have been classed as threatened comes from the impacts of future climate change on the bears’ habitat. You can read about these habitats, or 'Ecoregions', in the 2021 status report (PDF) issued by the IUCN/SSC Polar Bear Specialist Group. Ecoregions are based on the different ways in which the sea-ice behaves around the Arctic. Current analysis of subpopulations where data is sufficient clearly shows some are in decline, although some areas are too data-deficient to draw a conclusion so far. Further habitat degradation will, however, do nothing but increase the mounting threats to polar bears.
Last updated on 14 January 2024 by John Mason. View Archives
[DB] The topic of this thread is Polar bear numbers are increasing, not changes in sea-ice-extent minimums (cf this post on Kinnard et al 2011) nor about the opening of the Northwest Passage (another must-read is this post on Arctic sea ice extent).
Off-topic snipped.
Polar Bear populations are declining.
In 2005, the IUCN Polar Bear Specialist Group (PBSG) classified the Polar Bear as a vulnerable species. In 2009, they reported that of the 19 subpopulations of Polar Bears:
8 are declining
3 are stable
1 is increasing
7 are without sufficient data
This compares with, in 2005:
5 declining
5 five stable
2 increasing
7 data deficient
[Source]
· A decline in survival of female polar bears of all age classes, from 1194 to 806, between 1987 and 2011 in western Hudson Bay was due to earlier sea ice break-up in the spring and later freeze-up in the autumn.
· In 2010, polar bear numbers in the southern Beaufort Sea appeared to stabilize at 900 bears following a period of low survival during 2004-2006 that led to a 25-50% decline in abundance. However, survival of sub-adult bears declined during the entire period.
· Polar bear condition and reproductive rates have also declined in the southern Beaufort Sea, unlike in the adjacent Chukchi Sea, immediately to the west, where they have remained stable for 20 years. There are also now twice as many ice-free days in the southern Beaufort Sea as there are in the Chukchi Sea.
· Genetic studies indicate that polar bears have been through long and dramatic periods of population decline during the last one million years, and that during periods with little sea ice there have been multiple episodes of interbreeding between polar bears and brown bears.
[Source]
"The primary habitat for polar bears and their prey, sea ice, is declining rapidly in extent in all seasons, and particularly in summer, with concurrent and even more dramatic reductions in total volume (Laxon et al. 2013). Since the satellite record began in 1979, minimum sea ice extent has declined 13.3% per decade (see the essay on Sea Ice). Given the close association between polar bears, their primary prey and sea ice, climate warming remains the most significant threat to the long-term survival of this species (Stirling and Derocher 1993, Amstrup et al. 2008, 2010)."
[Source]
The evidence is clear: Polar Bear populations are declining.
I don't have the expertise to comment on it, but a non-peer reviewed paper claims the population is increaseing: https://peerj.com/preprints/2737/
Of course we know that there is less sea ice, but maybe the biologists don't understand something.
[JH] Sloganeering snipped.
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The author of your citation is Susan Crockford. She is an adjunct professor at the University of VIctoria. Her expertise is in the breeding and history of dogs. She is paid a monthly retainer from the Heartland Institute.
No sign of expertise in polar bears, although she lives closer to their habitat than I do.
The article was submitted on March 2 for comments but no-one has seen fit to comment. The impact factor of the journal is 2.2 which is very low. If you have $400 you can get a pre-print on PeerJ.
She purports to examine the status of polar bears when sea ice minimums are 3-5 mkm2. Current projections are less than 1 mkm2 in a few decades. Populations of long lived animals like polar bears change slowly in response to environmental changes.
Michael Sweet says about Dr Crockford "No sign of expertise in polar bears"
From Dr Crockfors's letter to the AIBS.
https://wattsupwiththat.com/2017/12/05/retraction-request-for-harvey-et-al-attack-paper-on-dr-susan-crockford/
"I am a professional zoologist with a Ph.D. and over forty years of experience and dozens of peer-reviewed papers on various topics, and also fails to mention that I have recently published a detailed academic critique on the issue of polar bear conservation status."
"...my Ph.D. dissertation on speciation included polar bears"
"In addition to my dissertation that features polar bears, I have an article on evolution in a peer-reviewed journal in which polar bears are prominently featured (Crockford 2003), and two official comments, with references, on polar bear hybridization (which is how official responses to published papers are handled in these two journals). I also have a paper in a peer-reviewed book chapter on ringed seals, the primary prey of polar bears (Crockford and Frederick 2011), and a peer-reviewed journal article on the paleohistory of Bering Sea ice, the habitat of Chukchi Sea polar bears (Crockford and Frederick 2007)."
According to http://wwf.panda.org/what_we_do/where_we_work/arctic/wildlife/polar_bear/population/
polar bear numbers are 22-31,000.
From the literature I've read no-one seriously disputes they are currently in decline but computer models say they are threatened by future climate change.
Michael Sweet said
"She is paid a monthly retainer from the Heartland Institute."
But she says...
I am not “linked with” nor do I “receive support” from The Heartland Institute or any other corporate-funded think tank.
either Michael Sweet or Dr Crockford is lying.
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Personal attack snipped. Also, note that the usage of sock puppets is frowned upon in this venue.
Bruce @72 ..... with all due respect, Dr Crockford's expertise in evolution/speciation & hybridization of polar bears has near zero relevance to the modern situation where there is an extinction threat to the species.
Polar bears are evolved for a specialized diet, and they do not have the fall-back position of an omnivorous diet (such as possessed by their ursine relatives). The polar bears' hunting habitat is heading rapidly toward 100% loss over the next one-to-two centuries, thanks to Arctic warming (per AGW).
Polar bear numbers (and importantly their condition) can be very difficult to determine accurately. It is a bold, very bold, scientist who undertakes to publicly express a complacent attitude about the survival of a specialized mega-fauna carnivore which is undergoing almost complete loss of habitat. Especially bold, for a scientist who is not a specialist "at the coal face".
It appears Dr Crockford holds an outlier opinion, and is also making a mountain out of a molehill when it comes to relevant expertise.
As to whether she is receiving financial benefits (from propaganda organizations such as Heartland, GWPF or other slush funds) in the form of a retainer or fee-for-service or stipend [see for instance the case of Emeritus Professor Lindzen or maybe Dr Judith Curry] or receiving non-cash benefits for speaking engagements etcetera ..... a cynic like you Bruce would of course wish see an absolutely categorical denial from her, that "none of the above" benefits apply to the present financial year nor any years of the past decade. Alas, it is all too easy for propaganda organizations to arrange for covert benefits of various types.
All too often in this world, Bruce, situations are more "gray" than you would wish.
Bruce,
According to this Desmog blog, Susan Crockford refused to respond to emails that asked aboout the money she gets from the Heartland Institute. Desmog provides links to internal Heartland documents that say they pay Crockford. Most of her claims are that she is a biological expert without mention of polar bears ie: " a paper in a peer-reviewed book chapter on ringed seals, the primary prey of polar bears (Crockford and Frederick 2011), and a peer-reviewed journal article on the paleohistory of Bering Sea ice,".
Susan Crockford has never studied polar bears, her "detailed academic critique" (mentioned first by you so it must be important to you) is a blog post written for the Heartlad Institute.
She is an adjunct professor which means she is part time in a position at the bottom rung of education. Hardly the position of an expert. I am an adjunct professor at a college so I know what that is.
Under no standard is she an expert in all biology as she claims.
I await your apology since I have provided documentation that Susan Crockford receives money from the Heartland Institute. Her denials are apparently false.
Recommended supplemental reading:
The global polar bear population is threatened by loss of sea ice, contrary to PragerU’s video claim by Vikki Forrester, Climate Feedback, May 18, 2020
KEY TAKE AWAY: There is no scientific evidence that the global polar bear population is growing in size. Climate change induced losses in sea ice habitat is the most important threat to polar bear survival. Two polar bear subpopulations have already been negatively impacted by sea ice loss.