Tag Archives: arctic sea ice

Record sea ice loss in 2007 had no effect on polar bears, Chukchi study confirms

One aspect of the recently published study on Chukchi Sea polar bears (Rode et al.2014 [now in print] 2013; see here and here) has not been stressed enough: their finding that the differences in overall condition between bears in the Chukchi and Southern Beaufort Seas came down to disparities in spring feeding opportunities and therefore, the condition of spring sea ice.

The fact that spring — not summer — is the most critical period for polar bears is something I’ve pointed out before (see here and here, for example) but it’s worth repeating at this time of year, when all eyes are on the annual ice minimum. It is often treated as a given that the decline in extent of summer sea ice in the Arctic since 1979 has been detrimental to polar bears. However, this is an assumption that we can now say is not supported by scientific evidence (see summary of that evidence here).

The results published by Rode et al. (2014 2013) not only add further support to the conclusion that declines in summer sea ice have not harmed polar bears, but should put the matter to rest – unless new evidence to the contrary is produced.

Chukchi bears, the report tells us, had more food available in the spring than Southern Beaufort bears (see map below) and this was the primary reason that bears were doing very well in the Chukchi and not quite as well in the Southern Beaufort. And because the polar bears for this study were captured and measured in mid-March to early May, from 2008 to 2011, they reflect spring-time conditions for 2008-2011 as well as year-round conditions from 2007 through 2010.

This means that the annual low ice extent for 2007 (record-breaking at the time), in the fall before this study began, had no discernible negative effect on either Chukchi or Southern Beaufort polar bears – and neither did similarly low annual minimums in two of the three remaining years of the study (Fig 1).

Figure 1. Sea ice extent at August 27, 2007 – the lowest extent that year (downloaded September 15, 2013 from IARC-JAXA, Arctic Sea-ice Monitor). At the time, it was the lowest extent recorded since 1979 (2012 broke that record). This (2007) was the fall before the Rode & Regehr study on Chukchi/Southern Beaufort polar bears began (2008-2011). The ice was almost as low in September 2008 and 2010, while 2009 was more like 2013.

Figure 1. Sea ice extent at August 27, 2007 – the lowest extent that year (downloaded September 15, 2013 from IARC-JAXA, Arctic Sea-ice Monitor). At the time, it was the lowest extent recorded since 1979 (2012 broke that record). This (2007) was the fall before the Rode & Regehr study on Chukchi/Southern Beaufort polar bears began (2008-2011). The ice was almost as low in 2008 and 2010, while 2009 was more like 2013.

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NSIDC says the sea ice minimum in 1964 was not different from 1979, 1981, or 2001

I just came across the National Snow and Ice Data Center (NSIDC) “monthly highlights” article for April 2013 (Glimpses of sea ice past), which turned out to be a rather more interesting story than it appeared at first glance.

The article chronicles the details of how NSIDC technicians pieced together photos taken by the Nimbus 1 satellite between August 28 and September 23, 1964 – of both the Arctic and the Antarctic – to create an estimate of sea ice extent at September 1964 for both regions. For the Arctic, this was the yearly minimum; for the Antarctic, the yearly maximum.

NSIDC scientist Walt Meier was part of this effort and he and colleagues Gallaher and Campbell recently published their findings in the journal The Cryosphere (Meier et al. 2013). For the Arctic estimate, they had to add in data from Alaskan and Russian sea ice charts because the 1964 satellite data was not complete. This means the ice extent figure they came up with is not a true ‘satellite only’ figure but a composite one.

One of the things they did in their analysis was to place the 1964 value on a graph of the more recent 1979-2012 data, which really helps put it into perspective (see Fig. 1 below).

Figure 1. This is Fig. 7 from the Meier et al. 2013 paper, to which I’ve added labels. Meier et al. call this a “time series of Arctic September sea ice extent.” The estimate for 1964 is the red dot on the far left (with its error bars), which I’ve circled (I also added the red label for 1964 and the black line). Note the Y-axis on the left goes to 3.0 million km2, not zero. The solid blue line is the monthly average for September from passive microwave data (1979-2012), and the blue dashed lines are a “three-day average of the high and low range of daily extents during the month.” The 1964 estimate of 6.90 ± 0.3 million km2 is just about identical to 1979, 1981, and 2001 and well within the average for 1979-2000. However, it’s significantly lower than the previous estimate of 8.28 million km2 for 1964 made by the UK Hadley Centre in 2003 (Meier et al. 2013:704).

Figure 1. This is Fig. 7 from the Meier et al. 2013 paper, to which I’ve added labels. Meier et al. call this a “time series of Arctic September sea ice extent.” The estimate for 1964 is the red dot on the far left (with its error bars), which I’ve circled (I also added the red label for 1964 and the black line). Note the Y-axis on the left goes to 3.0 million km2, not zero. The solid blue line is the monthly average for September from passive microwave data (1979-2012), and the blue dashed lines are a “three-day average of the high and low range of daily extents during the month.” The 1964 estimate of 6.90 ± 0.3 million km2 is just about identical to 1979, 1981, and 2001 and well within the average for 1979-2000. However, Meier and colleagues note it is significantly lower than the previous estimate of 8.28 million km2 for 1964, made by the UK Hadley Centre in 2003.

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Davis Strait polar bears again: body condition declined while population increased

This is a short follow-up to my last post on Davis Strait polar bears.

Today I’ll highlight a paper published last year (Rode et al. 2012) that had three of the same co-authors as the Peacock et al. (2012) paper I discussed on Monday – Lily Peacock, Mitch Taylor, and Ian Stirling contributed to both papers. Rode et al. (2012) deals with the issue of body condition (relative degree of fatness) in polar bears vs. changing levels of sea ice over time, and if you’ll pardon the pun, adds even more weight to the conclusion that declines in summer sea ice do not necessarily spell the disaster for polar bears we have been told is inevitable.

A polar bear near Thule, NW Greenland. Note the decidedly chubby back end on this bear, who looks well prepared for winter. Photo by Robin Davies. [details at my Quote Archive, Featured Quote #6]

A polar bear in the summer of 2012 near Thule, NW Greenland (part of the Baffin Bay subpopulation). Note the decidedly chubby back end on this bear, who looks well prepared for winter. Photo by Robin Davies.
[details at my Quote Archive, Featured Quote #6]

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Cannibalism update and insight on the timing of media hype

In my last post, I went over some of the spin and misrepresentation of fact contained in the claim by leading polar bear biologists Steven Amstrup, Ian Stirling and Andrew Derocher (Amstrup et al. 2006; Stirling and Derocher 2012) that cannibalism is on the increase because of the effects of global warming on Arctic sea ice.

I’ve had an opportunity to follow up on three points that puzzled me. Three relate to the Amstrup et al. paper that described three cases of cannibalism in the southeastern Beaufort Sea in 2004 and one to the incidents in western Hudson Bay in 2009. In the process, I found at least three more misrepresentations of fact and gained some insight on why these incidents of cannibalism were hyped so enthusiastically when they were. Continue reading