Although only in chart form, we do finally have an update on sea freeze dates for West Hudson Bay for 2016-2020 (not disintegration dates).
This graph data is published by Miller et al. 2022 extend it by five years published in 2017 by Castro de la Guardia and colleagues, containing histogram data for disintegration and freeze dates from 1979-2015 (exact dates available for 2005-2008 only).
It confirm a statement I made last monththat between 2016 and 2021”only one ‘late’ freezing year (2016) –but five very early.” Of course, 2021 is not included in this new dataset, so that would be “four very soon” to 2020.
This is part of Figure 2. Freeze data in the upper left (a):
Here is the small panel (a) by itself, enlarged (screenshot from the pdf), showing the trendline from 1991-2020:
Extracting numbers from graphs is time consuming and often inaccurate, but clearly polar bear experts don’t care: that’s all the public and their colleagues are being offered. .
In the list below, the first number is the year, the second number is Julian day of the year (e.g. 313) and the third day is the calendar day of the corresponding Julian day from mill paper compare to de al Guardia paper. For the past five years, I added my own review at the time, and since this is a screenshot here are the links for my estimates: for 2020 (when bears are killing seals on sea ice off the coast by October 31), 2019, 2018, 2017, 2016. I didn’t transcribe all the dates before 2005, just a select few.
Most items in the overlapping period between the two data sets are either identical or differ only by 1-3 days. However, the bolded parts change by almost a week or so (e.g. 2008, 2011), although there is no explanation in the Miller paper as to why this is the case:
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As you can see, the earliest freeze year is 1993 (though 1991, 1986 and 1978 are almost as early) and the closest year is 2016 (although 2009, 1998 and 1981 are almost as late depending on the date). depends on the dataset you look at).
With a potential failure rate of 2-3 days either way, the freeze is as early as 2020 as in 1978, 1979, 1986, 1991 and 1993 (earliest on record); Freezing days in 2017, 2018 and 2019 are similar to the 1980s average (de la Guardia et al. 2017).
Overall, Miller et al. found that there is no time trend in sea ice or the date of departure of polar bears from shore between 1991 and 2020, and perhaps counterintuitively, that the bears departed for the ice earlier in the years when the ice froze earlier.
This means that WH sea ice cover in the fall has not ‘reduced steadily’ over the past 30 years, and polar bears have not departed for the ice area later and later in the season during that time period, as many people mean.
However, although the authors collected out of date data on the body condition of females with independent offspring and young, these values are reported only as ‘vulnerability indicators’ , cannot be compared with the raw data collected in the 1970s and 1980s.
While these indicators indicate the body condition of females with five-year-old cubs (rather than those with one-year-old cubs)”decline over the past 30 years“, it is impossible to say how much compared with the detailed studies done before the 1990s (e.g. Derocher and Stirling 1992, 1995; Ramsay and Stirling 1988) or with those used to justify the claim. classified polar bears as ‘threatened’ in the United States List of Endangered Species (Regehr et al. 2007).
In other words, the body weight data – crucial to the argument that polar bears’ health is declining due to sea ice loss – is still being held.
Presenter
Castro de la Guardia, L., Myers, PG, Derocher, AE, Lunn, NJ, Terwisscha van Scheltinga, AD 2017. The sea ice cycle west of Hudson Bay, Canada, from a polar bear’s perspective. Flow of marine ecology 564: 225–233. http://www.int-res.com/abstracts/meps/v564/p225-233/
Derocher, AE and Stirling, I. 1992. Population dynamics of polar bears in western Hudson Bay. pg. 1150-1159 in DR McCullough and RH Barrett, ed. Wildlife 2001: Populations. Elsevier Science. Publisher, London, UK
Derocher, AE and Stirling, I. 1995. Temporal changes in polar bear reproduction and body mass in western Hudson Bay. Canadian Journal of Zoology seventy three:1657-1665. http://www.nrcresearchpress.com/doi/abs/10.1139/z95-197
Miller, EN, Lunn, NJ, McGeachy, D., and Derocher, AE 2022. The autumn migration of polar bears (Ursus maritimus) in Hudson Bay, Canada. Polar biology 45:1023-1034.
Ramsay, MA and Stirling, I. 1988. Reproductive biology and ecology of female polar bears (Ursus maritimus). The London Zoological Journal 214:601-624. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1988.tb03762.x/abstract
Regehr, EV, Lunn, NJ, Amstrup, SC & Stirling, I. 2007. Effects of earlier sea ice melt on the survival and population size of polar bears in West Hudson Bay. Wildlife Management Magazine 7first: 2673-2683. There is a wall fee, registration required. http://onlinelibrary.wiley.com/doi/10.2193/2006-180/abstract
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