Category Archives: Sea ice habitat

Sea ice is critical habitat for polar bears from late fall through late spring only

Sea ice is said to be “an essential habitat for polar bears” but that’s an overly simplistic advocacy meme as ridiculous as the “no sea ice, no polar bears” message with which the public is constantly bombarded. Polar bears require sea ice from late fall to late spring only: from early summer to mid-fall, sea ice is optional. Historical evidence of polar bears that spent 5 months on land during the summer of 1874 proves an extended stay ashore is a natural response of polar bears to natural summer ice retreat, not a consequence of recent human-caused global warming. Sea ice is a seasonal requirement for polar bears: it’s not necessary year round.

polarbears-arcticnatlwildliferefuge-suzannemiller-usfws_labeled_sm

[This PBI newsletter from 2011 repeats this meme and Andrew Derocher’s recent tweet conveys a similar message (“Sea ice loss = habitat loss for polar bears”)]

As long as sea ice is available from late fall through late spring (December to early June) and accompanied by abundant seal prey (sometimes it isn’t, see Derocher and Stirling 1995; Stirling 2002; Stirling et al. 1981, 1982, 1984), polar bears can survive a complete or nearly complete fast from June to late November (and pregnant females from June to early April the following year). That’s the beauty of their Arctic adaptation: fat deposited in early spring allows polar bears to survive an extraordinary fast whether they spend the time on land or sea ice.

Young and very old bears, as well as sick and injured ones, are the exception: these bears often come ashore in poor condition and end up dying of starvation — as a much-publicized bear on Baffin Island who likely had a form of cancer did last summer (Crockford 2018). Competition with bigger, stronger bears means these bears can’t keep what they are able to kill and they are most often the bears who cause problems. Starvation is the leading natural cause of death for polar bears because if they cannot put on the fat they need in spring, they will not survive the low food months of summer and winter, whether they are on land or out on the sea ice (Amstrup 2003). Continue reading

Just look at what the ‘global heat wave’ is doing to polar bear sea ice habitat!

According to the Guardian (9 July 2018), there is a “global heat wave” going on right now.

In Siberia, the heat is supposedly “completely unprecedented” and will surely (we are told) impact Arctic sea ice — the habitat of the iconic polar bear.  Yet a comparison of previous years shows little to no impact on sea ice: there is more ice present than there was in 2007.

Polar Bear Breaks Ice

Said The Guardian:

“But though we cannot say definitively that the current heatwave is caused by carbon emissions, it fits the pattern of long-term changes that we call climate. It is part of a global phenomenon, even if not the most important part. The really significant change is happening in eastern Siberia at the moment, where a completely unprecedented heatwave is warming that Arctic coastline, with consequences that are unpredictable in detail but surely bad on a large scale.” [my bold]

The heat — which some folks admit they not only expect during this season called summer but anticipate with joy — has been around since late June, with several locales outside Siberia affected, including southern Ontario, Quebec, Los Angeles CA, Britan, many locations in the eastern USA, Europe.

With so many locations across the Northern Hemisphere experiencing very hot weather over the last few weeks (maybe record-breaking, maybe not), let’s take a look at what all that heat is doing to Arctic sea ice compared to previous years.
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First fatal polar bear attack in W. Hudson Bay since 1999 occurred yesterday in Arviat [corrected]

A brave young father from Arviat on the northwest coast of Hudson Bay was killed yesterday evening by a polar bear while trying to protect his children.

Walking bear_129029633_web size

Aaron Gibbons, 31, was the nephew of Gordy Kidlapik, who follows this blog and my twitter account. Gordy has often sent me useful local information and perspectives from Arviat, which is in Nunavut (north of Churchill, Manitoba).

It was heartbreaking to hear this news firsthand from Gordy:

Arviat with Churchill_Google maps

More below and to follow as further details emerge. My sincere condolences to Gordy and his family – what a horrific loss.

UPDATE: 4 July 2018 9:00 pm PT. See correction below regarding the last fatal WHB attack, which was in 1999 (Rankin Inlet), not 1983 as my original title read. My apologies but as you’ll see, the newspaper didn’t get it right either.

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Spring feeding for polar bears is over – sea ice levels are now largely irrelevant

Polar bears in virtually all regions will now have finished their intensive spring feeding, which means sea ice levels are no longer an issue. A few additional seals won’t make much difference to a bear’s condition at this point, except perhaps for young bears that haven’t had a chance to feed as heavily as necessary over the spring due to inexperience or competition.

Polar bear feeding by season simple_Nov 29 2015

The only seals available on the ice for polar bears to hunt in early July through October are predator-savvy adults and subadults. But since the condition of the sea ice makes escape so much easier for the seals to escape, most bears that continue to hunt are unsuccessful – and that’s been true since the 1970s. So much for the public hand-wringing over the loss of summer sea ice on behalf of polar bear survival!

Polar bears in most areas of the Arctic are at their fattest by late June. They are well prepared to go without food for a few months if necessary – a summer fast is normal for polar bears, even for those that spend their time on the sea ice.

Putting on hundreds of pounds of fat in the spring to last through periods of food scarcity later in the year (at the height of summer and over the winter) is the evolutionary adaptation that has allowed polar bears to live successfully in the Arctic.
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Hudson Bay sea ice update: more ice in the east than usual but less in the west

There’s almost more blue in the Canadian Ice Service “departure from normal” charts for this week than red, which means more sea ice than usual, especially in the eastern half of the bay and northern Labrador. Eventually, the melting ice will force polar bears ashore where they will fast for 4-5 months, living off the fat they’ve put on over the spring feeding season.

Hudson Bay weekly departure from normal 2018 June 25

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Hansen’s 1988 climate change testimony was the answer to Stirling’s polar bear problem

Last week’s media coverage made me realize that James Hansen’s testimony to a US Senate committee in 1988 provided well-timed answer to a vexatious problem facing polar bear biologist Ian Stirling. Thirty years ago, Stirling was struggling to understand why polar bear productivity in Western Hudson Bay had dropped.  He was ripe for the suggestion from Hansen (and his follow-up paper) that human-caused global warming could be the explanation. An interview with Stirling and colleague Andrew Derocher published in 2016 helps connect the dots.DA-IS-measuring_Ian Stirling

Many bears were in poor condition in the fall of 1983 (Calvert et al. 1986:19, 24; Ramsay and Stirling 1988). In general, the 1980s saw weights of bears decline and cub mortality increase, with a marked increase in the loss of whole litters over what had been documented in the 1960s and 1970s (Derocher and Stirling 1992, 1995).

Until Hansen and climate change came along,  density-dependent effects (such as the number of bears out-pacing food supply) were seen as the most likely explanation. But sea ice decline blamed on human-caused global warming was suddenly a new possibility that Stirling soon embraced (Stirling and Derocher 1993). By the late 1990s, sea ice coverage on Hudson Bay had indeed declined but the correlation with polar bear productivity produced a weak trend that was not statistically significant (Stirling et al. 1999).

The 1999 Stirling paper did not provide scientific evidence to explain the 1980s decline in productivity as much as it presented a novel scapegoat to blame when a more plausible explanation could not be made.

Bottom line: Global warming could not have been the proximate cause of the productivity changes in WH polar bears documented during the 1980s but Stirling spent the next two and a half decades vigorously pushing climate change as the cause of all polar bear ills. Continue reading

Hudson Bay ice update: more thick first year ice habitat for polar bears in 2018 than 2004

Despite pronouncements from one polar bear specialist that “ice in Hudson Bay is in rapid retreat” a look back in time shows that there is more thick first year ice over the Bay this year for the week of the summer solstice than there was in 2004 – and much less open water than 1998.

Lunn et al 2016 EA cover image WH bear

Below, 2018, June 18 (the week of the summer solstice):

Hudson Bay weekly stage of development 2018 June 18

Compare the above to the same week coverage chart for 2004, below:
Hudson Bay weekly stage of development 2004_June 21

Ice coverage for some other recent years are shown below compared to 1998, the year the ice breakup pattern on Hudson Bay changed. Speed and melt sequences vary according to the amount of thick first year ice present, discussed previously here.

PS. If you’re wearing white today, flaunt it! Tell your friends and colleagues that you’re celebrating the success of polar bears despite such low summer sea ice since 2007 that 2/3 of them were predicted to disappear.
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