Tag Archives: summer

September minimum 2015 looks like the earliest end of Arctic melt season since 2007

Polar bear habitat in the Arctic Basin this year appears to have reached its apex days earlier than average. As of 12 September, freeze-up of Arctic sea ice had begun. Unless something dramatic happens over the next few days, this will make 2015 the earliest September minimum since at least 2007, using NSIDC data.1

masie_all_zoom_v01_2015252_4km

The two lowest September ice extents (2007 and 2012) were also both later than average; this year’s minimum is the fourth lowest (see chart below).

Of course, all this fuss about how low the September minimum gets is irrelevant to polar bears: they are either on land or in the Arctic Basin, and virtually all are living off stored fat no matter where they are (see Arctic Basin bear here). What matters is when the refrozen ice reaches pregnant females that have preferred denning spots onshore (like in Svalbard) or for bears onshore waiting to return to the ice to hunt (like Davis Strait, and Western and Southern Hudson Bay bears). We won’t know that until October (for Svalbard) or November (for E. Canada).

Again, no sea ice death spiral or polar bears in peril because of it.

UPDATE 15 September 2015, 11:00 am PDT: Just published at the NSIDC website, 2015 minimum has been (tentatively) called at 4.41 mkm2, confirming my figure taken from their interactive graph (see below). However, despite the fact that their own data show that sea ice extent stayed at that value for three days, NSIDC has chosen the last day of that 3-day period rather than the first to represent the 2015 minimum. Go figure. That makes 2015 tied with 2011 for the earliest date for their official records, which seems more than a little self-serving and means I’m not changing the title of my post. NSIDC have also modified slightly some of the official extent figures for past minimums (added below) but it doesn’t really change anything.
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Polar bears are not hungriest in summer when scientists are busy in the Arctic

Polar bears are leanest – and therefore, hungriest – at the end of March, not in the summer, as chemist Crispin Halsall stated in a recent article about working in the Arctic.

Polar bear feeding budget_PolarBearScience_6Sept2015

Recent September 1st stories by CNN and the BBC, based on a press release by WWF Russia on 27 August 2015, that five bears in the southern Kara Sea were hanging around a weather station and frightening workers there, apparently prompted chemist Crispen Halsall to make a nonsensical statement about polar bears being at their “hungriest” in summer (first here, reproduced here and picked up yesterday (September 5) by The Guardian here).

“In the path of the polar bears: what it’s like to be an Arctic scientist” (4 September 2015; Crispin Halsall, Reader in Environmental Chemistry at Lancaster University) had this to say:

“The case of Russian scientists trapped in their remote Arctic base by a group of inquisitive yet hungry polar bears does not come as a surprise. By late summer, Arctic sea ice is at a minimum and polar bears are effectively landlocked in coastal areas eagerly awaiting the return of ice during the autumn freeze and the chance to hunt seals again.

The Arctic summer is also the time of year when scientific activities are at their maximum, with bases operating at capacity and fieldwork operations at full flow, particularly in tundra and coastal regions. Polar bears are hungriest when scientists are busiest – “encounters” are inevitable. [my bold]

Polar bears are leanest – and therefore, the hungriest – at the end of winter (when it is more likely to kill with the intent to consume human prey) as stated clearly by Stirling and Øritsland (1995:2603):

Polar bears reach their lightest weights for the year in late March, just prior to the birth of the next cohort of ringed seal pups, which also suggests that it is the success of their hunting in spring and early summer that gives them the body reserves they need to survive through the rest of the year.” [my bold]

A polar bear that has not fed properly in spring – because it was young and inexperienced, too old or too young to defend its kills from bigger, stronger bears, or simply sick or injured – it might be unusually hungry in summer but it’s not the norm.  Polar bears eat nothing or very little over the summer (whether on land or on the ice) because they live off their stored fat – the physiological condition known as ‘fasting.’

The photos and video in the September 1, 2015 BBC story of the Russian bears shows this: the bears are fat, not skinny (“Video caption: Five bears settled near the weather station on the north Russian island of Vaygach, as Frankie McCamley reports”):

Beseiged by bears Russia BBC video Sept 1 2015

Polar bears might approach humans working in the Arctic during the summer because they are curious and/or bored, and they might attack and even eat humans because they have a drive to eat whenever the opportunity arises. But it’s not because they are “hungriest” in the summer.

References
Stirling, I. and Øritsland, N. A. 1995. Relationships between estimates of ringed seal (Phoca hispida) and polar bear (Ursus maritimus) populations in the Canadian Arctic. Canadian Journal of Fisheries and Aquatic Sciences 52: 2594 – 2612. http://www.nrcresearchpress.com/doi/abs/10.1139/f95-849#.VNep0y5v_gU

Tracking polar bears – two S. Beaufort bears spent August 2015 on ice that doesn’t exist

Two out of seven polar bears with collars in the Southern Beaufort Sea either spent the month of August on ice that satellites couldn’t see – or they spent the entire month swimming around the Beaufort. Which seems most likely?

Thin ice Lisa Robbins Sept 15 USGS_04

See previous discussions here and here regarding the problem satellites have in accurately detecting melting ice. The presence of these two bears is evidence that there is more polar bear habitat than satellites record as officially present. This was also an issue for Hudson Bay bears earlier this year.

Five out of the seven visible females were on the ice in August – but are the other six bears that were visible last month spending the summer in the Arctic Basin like the one I reported last week? Or have their collars actually failed or dropped off? USGS isn’t saying.

See the August track map below, from the USGS Tracking Polar Bears website1 and a sea ice map.
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Polar bear habitat update – more ice than 2012 when all the bears didn’t die

Overall, the situation is better than many recent years – lower than average but higher than even 2012 and 2007, when all the polar bears didn’t die despite record-low extents for September. In several areas of the Eastern Arctic, sea ice levels continue to run higher than average. There is plenty of ice in the Arctic Basin for polar bears spending the summer under the midnight sun.

masie_all_zoom_v01_2015237_4km

According to NSIDC MASIE (see map above):

2007 at 25 August – 5.2 mkm2
2012 at 25 August – 4.9 mkm2
2015 at 25 August – 5.3 mkm2
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Summer habitat for most polar bears is either shoreline or sea ice in the Arctic Basin

At this time of year, sea ice extent numbers are meaningless for polar bears.  The extreme low September minimum of 2012 – when masses of polar bears didn’t die – showed rational people that this is true. Even the low 2007 summer extent, which hit earlier in the season than 2012, had little to no negative impact.

Greenland W coast_Female w cubs_2006_Mads Heide-Jorgensen_NOAA sm

In late summer, bears outside the Canadian Archipelago either retreat to shore or stay on the sea ice as it retreats north into the Arctic Basin (see image below, click to enlarge).  Most bears in the Archipelago have ice year round, so life doesn’t change much. This means that it does not matter to polar bears how much area the Arctic Basin ice covers in September – for their needs, 1.0 mkm2 would be plenty.

Sea ice and summer refuges for polar bears_17 Aug 2015

Still, Southern Hudson Bay polar bears had extended hunting opportunities in July this year (whether or not they hunted successfully) and for this date, Hudson Bay had more ice remaining than any year on record. Yes, more than even 1992 but only by a few percent. See charts and maps below.

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Well-fed polar bears onshore at height of summer easily deterred by noise, CBC reports

From the CBC this morning, we have the report of a female polar bear and her cub paying a visit to an Nunavut campsite near Chesterfield Inlet in northwestern Hudson Bay, which is technically within the boundary of the Foxe Basin polar bear subpopulation.

Maggie Putulik photo, 29 July 2015 Chesterfield Inlet, Nunavut.

Maggie Putulik photo, 29 July 2015 Chesterfield Inlet, Nunavut.

These are not the desperate bear victims of global warming we have been warned about by polar bear specialists but well-fed curious ursids not averse to an easy meal if there’s one to be had. Such bears are easily deterred by a loud noise. Note this was the second visit by polar bears this Nunavut family had experienced at this location within a three-week period – two other bears had stopped by earlier. Note that ice in this region of Hudson Bay broke up earlier than usual this year yet these bears seem to be in fine condition and can expect the first fall ice of the season (freeze-up) to appear in their neighbourhood, see maps below.
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Summer polar bear habitat then & now – little impact from 2007 record-breaking sea ice low

Sea ice looks low for this time of year but how does it compare to 2007, when summer ice habitat for polar bears hit a record-breaking low?  What can the impact of 2007 ice levels on polar bears tell us about what to expect this year?

Sea ice at 2015 Aug 8 vs pb status map_Aug 9 2015 sm

By this date in 2007 (8 August, Day 220, NSIDC Masie map below), there was almost 1 million km2 less ice than there is this year (map above). However, look which polar bear subpopulations not only survived, but thrived, through the 2007 low ice summer: Chukchi Sea, Southern Beaufort, Barents Sea, Davis Strait, Foxe Basin, Western Hudson Bay, and Southern Hudson Bay. That’s all of the subpopulations for which we have recent data.

There is more than a month left in the melt season, of course. However, while 2012 finished with a lower minimum ice extent due to a massive mid-August storm that broke up a lot of ice (Simmonds and Rudeva 2012), by the end of the first week of August (i.e, the 8th), there was more  ice in 2012 than in 2007 and a bit less than this year (2012, 6.3 mkm2; 2007, 5.6 mkm2; 2015, 6.5 mkm2).

This means if less summer ice for a longer period of time impacts polar bear health and survival, conditions in 2007 should have had a noticeable impact on polar bears around the world. They didn’t. That suggests even if this September sea ice minimum is as low as 2007, it won’t have any negative impact on polar bear health or survival. The most profoundly negative documented impacts have come from thick sea ice in spring or  suboptimal spring snow levels (Crockford 2015) and the evidence shows that variation in the extent of summer ice is simply irrelevant to polar bears.

Sea ice at 2007 Aug 8_polarbearscience
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