Tag Archives: prolonged ice-free season

Journalists still pushing the “polar bears eat snow geese story,” as if it matters

I wrote about this issue in January (January – and journalists are still pushing it).

Courtesy NY Times, Sept. 22 2014.

Figure 1. Courtesy NY Times, Sept. 22 2014. Click to enlarge.

This month, the New York Times (September 22, 2014 James Gorman, “For Polar Bears, a Climate Change Twist”) is pushing it big-time (and so it’s been picked up elsewhere, like by the Anchorage Daily News).

Myths and misinformation about this phenomenon dispelled below.
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Breakup date average for W. Hudson Bay is July 1 – this year, it’s late again

In the last few days, ice coverage on Western Hudson Bay finally dropped below the 30% level that now defines ‘breakup’ for polar bears: a few bears near Churchill started to come ashore late last week but most will stay on the ice until the end of July. That means breakup this year was unofficially July 8th, a week later than average (July 1) for the third year in a row.
Sea ice extent Canada 2014 July 7 CIS

Don’t’ tell that to the folks at Polar Bears International, though, because they’re busy telling people that the ice-free season for Western Hudson Bay bears is now longer than it was before the 1990s. What they mean is that the overall trend is toward early breakup dates.

But what they don’t admit is that over the last 44 years, breakup was a full two weeks earlier than average for Western Hudson Bay only six times and only three of those early breakups occurred within the last 13 years. See the calculations below and see what you think.

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Churchill polar bears eat more caribou and geese now than in 1968 because there are more caribou and geese, new research reveals

The press release (pdf here) issued by the American Museum of Natural History (AMNH) a few days ago, regarding several recent papers on polar bear consumption of terrestrial foods around Churchill, Manitoba (Western Hudson Bay), left a lot to be desired in terms of relaying accurate information.

21 August 2021 UPDATE: I have amended this post to correct some comments I made originally about the definition of ‘spring breakup’ of sea ice on Hudson Bay. While the ice indeed begins to break up in spring (usually defined for the Arctic as April-June, bears rarely come ashore before July 1 (summer being July-September). Confusion comes from the standard meteorological method of the defining ‘breakup’ for Western Hudson Bay as the date when ice coverage drops below 50% of the area, rather than the newer, more relevant date when most polar bears have actually come ashore after the date ice coverage reaches 30% (Castro de la Guardia et al. 2017). Using the modern method, the earliest breakup date was in 1999 (17 June), which was still the case in 2021).

Recent research on polar bear diets by Robert Rockwell and Linda Gormezano, it says, suggests that an increase in the consumption of caribou and snow geese since 1968 is a sign that the polar bears are nutritionally stressed due to recent sea ice changes in spring (blamed on global warming) but may be adapting by changing their summer/fall diet.

As the AMNH press release puts it:

polar bears in the warming Arctic are turning to alternate food sources.”

Figure 1. Polar bear feeding on a caribou carcass, taken July 26, 2010. This photo was included in one of the papers cited in the January 2014 press release (Gormezano and Rockwell 2013:3518) and was clearly taken from the air. The caption in the paper says simply, “a polar bear looks up from the recently killed caribou it was eating,” so the bear may not have killed the caribou – some other predator (wolf or grizzly) may have made the actual kill. The dark spots on the bear appear to be flies. Credit Copyright American Museum of Natural History/ R. Rockwell.

Figure 1. Polar bear feeding on a caribou carcass, taken July 26, 2010, from the air. This photo was included in virtually all media reports and in Gormezano and Rockwell (2013a:3518, Fig. 3). The caption in the paper says, “a polar bear looks up from the recently killed caribou it was eating,” implying the bear may not have actually killed the caribou – some other predator (wolf or grizzly) may have made the kill. The dark spots on the bear appear to be flies. Credit: Copyright American Museum of Natural History/R. Rockwell.

However, the AMNH press release fails to mention – as the papers it publicizes certainly do – that Western Hudson Bay populations of caribou and snow geese have increased exponentially since a similar polar bear diet study was done in 1968/69. In other words, there were hardly any caribou or geese around back in the late 60s — little wonder polar bears weren’t eating any.

While evidence of polar bears consuming caribou and geese in recent years is certainly an “increase” over late 1960s levels, that fact says more about the status of caribou and geese populations than it does about polar bears and global warming. Media outlets that quoted the press release verbatim, as many do these days (e.g. here, here, and here), missed this essential part of the story – and of course, so did their readers.

[one story picked up the goose population increase and another revealed the caribou population increase, but none that I saw caught both]

In addition, the AMNH press release makes this erroneous statement that was picked up by every media outlet I saw except one (either exactly as written or reworded slightly):

Climate warming is reducing the availability of their ice habitat, especially in the spring when polar bears gain most of their annual fat reserves by consuming seal pups before coming ashore for the summer.” [my bold]

The earliest breakup dates since 1991 for Western Hudson Bay, where this research was done, have been mid-June (according to the most recent study by Cherry et al. 2013) and for the last few years breakup has occurred in July.

Overall, the press release and resulting media reports seem to be further examples of hyping global warming at the expense of the actual science involved and I have to agree with Andrew Derocher’s interpretation of the significance of terrestrial food items for polar bears. See what you think.
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Polar bear habitat update, end of November 2013

Freeze-up in the Arctic (~October-November) is important to polar bears because for those animals that have spent the ice-free period on shore (not all do), it marks the end of their summer fast — they can finally resume seal hunting.

Polar bears in the most southern regions, like Southern Hudson Bay, Western Hudson Bay, and Davis Strait (see Fig. 1), routinely experience the longest ice-free period. As these bears all spend the summer on shore, they appreciate a timely return of the ice.

 Figure 1. Polar bear subpopulations defined by the IUCN Polar Bear Specialist Group (PBSG), with a few extra labels added. I’ve rotated the original map 90 degrees (right) to make it easier to relate to the ice maps below. WH is Western Hudson Bay. Courtesy PBSG.  Click to enlarge.

Figure 1. Polar bear subpopulations defined by the IUCN Polar Bear Specialist Group (PBSG), with a few extra labels added. I’ve rotated the original map 90 degrees (right) to make it easier to relate to the ice maps below. WH is Western Hudson Bay; SB is Southern Beaufort. Courtesy PBSG. Click to enlarge.

Southern Hudson Bay bear populations routinely experience an ice-free season that is just as long as it is for Western Hudson Bay bears. However, Southern Hudson Bay polar bears numbers have remained stable over the last 30 years. Some folks insist that Western Hudson Bay bear numbers are shrinking to a worrisome degree, despite indications that the recent decline could be nothing more than a return to sustainable levels after a rapid population increase in the late 20th century (similar to changes documented for the Davis Strait and Barents Sea subpopulations).

Have a look at how sea ice – essential polar bear hunting habitat – has developed within these regions over the last 10 days or so (end of November 2013) and how November 2013 compares to November 1979. The ice maps tell the freeze-up story.
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Polar bears have not been harmed by sea ice declines in summer – the evidence

PB  logo colouredThe polar bear biologists and professional activists of the IUCN Polar Bear Specialist Group (PBSG) continue to insist that since 1979 increasingly smaller amounts of Arctic sea ice left at the end of summer (the September ice minimum) have already caused harm to polar bears. They contend that global warming due to CO2 from fossil fuels (“climate warming” in their lexicon) is the cause of this decline in summer ice.

In a recent (2012) paper published in the journal Global Change Biology (“Effects of climate warming on polar bears: a review of the evidence”), long-time Canadian PBSG  members Ian Stirling and Andrew Derocher (both of University of Alberta) summarized their position this way:

“Climate warming is causing unidirectional changes to annual patterns of sea ice distribution, structure, and freeze-up. We summarize evidence that documents how loss of sea ice, the primary habitat of polar bears (Ursus maritimus), negatively affects their long-term survival”

I’ve spent the last year examining their evidence of on-going harm, but in addition, I’ve looked at the evidence (much of it not mentioned in the Stirling and Derocher paper1) that polar bears have either not been harmed by less sea ice in summer or have thrived in spite of it.

This is a summary of my findings. I’ve provided links to my original essays on individual topics, which are fully referenced and illustrated. You are encouraged to consult them for complete details. This synopsis (pdf with links preserved, updated; pdf with links as footnotes, updated) complements and updates a previous summary, “Ten good reasons not to worry about polar bears” (pdf with links preserved; pdf with a foreword by Dr. Matt Ridley, with links as footnotes).

Update 8 September 2013: to include links to my post on the recently published Chukchi population report; updated pdfs have been added above.

Update 22 January 2014: added figure comparing March vs. September sea ice extent using the same scale, from NOAA’s “2014 Arctic Report Card,” discussed here.
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Biologists spreading misinformation: hybridization with grizzlies not due to polar bears moving inland

A paper published last week in the journal Science, written by a team of biologists and atmospheric scientists, expounds on a possible dire future for a range of Arctic animals. It’s called, “Ecological consequences of sea-ice decline” and surprisingly, polar bears are discussed only briefly.

However, with the inclusion of one short sentence, the paper manages to perpetuate misinformation on grizzly/polar bear hybridization that first appeared in a commentary essay three years ago in Nature  (Kelly et al. 2010)1. The Post et al. 2013 missive contains this astonishing statement (repeated by a Canadian Press news report):

Hybridization between polar bears and grizzly bears may be the result of increasing inland presence of polar bears as a result of a prolonged ice-free season.

Lead author of the paper, Professor of Biology Eric Post, is quoted extensively in the press release issued by his employer (Penn State University, pdf here). In it, Post re-states the above sentence in simpler terms, removing any doubt of its intended interpretation:

“… polar and grizzly bears already have been observed to have hybridized because polar bears now are spending more time on land, where they have contact with grizzlies.

Both statements are patently false. All recent hybridization events documented (2006-2013) occurred because a few male grizzlies traveled over the sea ice into polar bear territory and found themselves a polar bear female to impregnate (see news items here and here, Fig. 1 below). These events did not occur on land during the ice-free season (which is late summer/early fall), but on the sea ice in spring (March-May).

Grizzlies have been documented wandering over the sea ice of the western Arctic since at least 1885 (Doupe et al. 2007; Fig. 2, below) and the presence in this region of hybrid grizzly/polar bear offspring is not an indicator of declining summer sea ice, whether due to global warming or natural causes, or some combination thereof.

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