Post by Susan Crockford. Original post here.
It’s hard to believe that a polar bear specialist would claim that their predictions have come true, given the facts of the matter: that polar bears arguably number over 30,000 worldwide and regions with the most dramatic sea ice declines have not documented reduced polar bear health or survival. But in mid-July this year, Andrew Derocher – one of the field’s most vocal promoters – did just that: proclaimed on twitter that “virtually all of our predictions are coming true.” Except, none of them did, especially the most widely-promoted one, which failed spectacularly.
The paper Derocher referred to in his tweet from 1993 was called ‘Possible impacts of climatic warming on polar bears‘ and it didn’t really contain predictions so much as speculations, which Ian Stirling hoped would distract from the odd patterns in polar bear health and survival he had documented in Western Hudson Bay but couldn’t explain [declining body condition, lowered reproductive rates, reduced cub survival, and increased polar bear-human interactions] (Stirling and Derocher 1993; Crockford 2019). As stated in the abstract of that paper “Although most of these changes are currently detectable in the polar bears of western Hudson Bay, it cannot yet be determined if climatic change is involved.” That’s right: those changes in polar bears were happening even before the changes in sea ice breakup and freeze-up patterns currently blamed on climate change had occurred. Similar changes have happened since but are now blamed on climate change .
As an aside, it’s worth noting that the delay in sea ice breakup mentioned in that paper that occurred in 1992 (said to have been “the opposite of what would be predicted by climate warming“) was blamed on the eruption of Mt. Pinatubo in the Philippines. Oddly, however, there has been no external causation offered for the similarly late breakup and early freeze-up of sea ice that happened more than two decades later, in 2019.
The real predictions came decades later (e.g. Stirling and Derocher 2012), with prophesies of increased cannibalism, deaths by mass starvation, drowning and den collapses, none of which happened (Crockford 2019).
But let’s focus on the big one: the prediction that failed spectacularly. Derocher would rather forget Steven Amstrup’s 2007 prediction that 2/3 of polar bears would be gone after 10 years of 40% less summer ice (Amstrup et al. 2007; USGS 2007).
This month, it will be 14 years since the most widely-promoted polar bear prediction of all time was made by US Geological Survey biologist Steven Amstrup and his colleagues. Sea ice dropped to a new low that September (see above, from Amstrup et al. 2008) and ever since, with a bit of up and down, September ice extent has been about the level that sea ice experts in 2005 predicted would be upon us by 2050 (ACIA 2005; Stroeve et al. 2007). Ahead of schedule! Worse than they thought! Fourteen years of mid-century sea ice!
Above: Predicted sea ice decline vs. actual (to 2007), from Stroeve et al. 2007.
And while it looks likely that ice extent in September 2021 won’t be anywhere as close to 2012 as Derocher feared in July (see below), it will still be at levels considered to be devastating for polar bears (i.e. between about 3-5 mkm2, within measurement error, for at least 8 out of 10 years):
Same graph as above but at 11 September 2021 vs. 2020, 2012 and 2007 (bright blue is 2021):
See graph below for September sea ice to 2020 (NSIDC, to 2019, 2020 added):
The predicted decline of polar bear numbers was tied to September sea ice decline: the ice cover dropped but polar bear numbers didn’t (Crockford 2017, 2019; Crockford and Geist 2018). Derocher and his chums can denigrate me all they like (and oh, how they love to do so) and call me a ‘denier’ and imply I am nothing but a blogger but these things do not change the facts: I am a zoologist with a Ph.D. just like many of them and polar bear numbers did not decline by 67% (i.e. a drop of about 17,300) despite 14 years of sea ice conditions they said would devastate the global population.
They have no explanation for this utterly failed prediction except to insist they always expected different subpopulations to decline at different rates. Except that’s not actually true but you have to look at the papers I have archived from 2007 to see it (Amstrup et al. 2007; Durner et al. 2007; Hunter et al. 2007; Regehr et al. 2007; USGS 2007).
What they said was that polar bears in Seasonal ice areas (Western and Southern Hudson Bay, Foxe Basin, Davis Strait, Baffin Bay) and Divergent ice areas (Southern Beaufort Sea, Chukchi Sea, Laptev Sea, Kara Sea, Barents Sea) – green and purple areas in the map below (from Regehr et al. 2016) – would be hit with comparable declines in ice and that polar bear numbers in these area would decline similarly. Nothing like that happened.
What has happened?
Sea ice decline has been moderate in Seasonal ice regions (which include the furthest-south habitats) and dramatic in Divergent regions. In Southern and Western Hudson Bay, ice declined suddenly in 1998 (Castro de la Guardia et al. 2017) but hasn’t changed much since, except it was back to 1980 levels in 2019 and 2020. Population levels are said to have declined in 2016 in both regions but the amount was statistically insignificant (Crockford 2021). Foxe Basin and Davis Strait bears appear to have been thriving despite the ice declines, and Baffin Bay bears are holding their own (Crockford 2021; Peacock et al. 2013; Stapleton et al. 2012; SWG 2016).
In the Barents Sea, summer ice extent has declined six times as much as ice in Western Hudson Bay and the Chukchi Sea – more than any other subpopulation – but the bears are still doing fine with no sign of a population decline (Aars 2018; Aars et al 2017; Lippold et al. 2019; Regehr et al. 2016). Southern Beaufort Sea bear numbers declined a decade ago but numbers held steady up to 2015 despite continued summer sea ice declines (Atwood et al. 2020; Crockford 2021); then in 2019, a record number of fat bears were counted ashore in July. Like Barents Sea bears, those in the Chukchi Sea are doing very well: bears are in excellent condition and reproducing well with no signs of a population decline despite a much longer open water season than in the 1980s (Conn et al. 2021; Regehr et al. 2018; Rode et al. 2014, 2018). Condition of bears and their abundance in the Laptev Sea are unknown but there is no reason to expect they are doing worse than those in the Chukchi or Barents Seas (Crockford 2019, 2021). After all, primary productivity in the Laptev Sea was much higher in 2020 than it was in the 1980s (Frey et al. 2020), which means more food for every species higher up the food chain, including bears.
The increased spring rain events they predicted would happen along with earlier sea ice breakup never materialized. Neither did repeated deaths by drowning during the ice-free season or marked increases in incidents of cannibalism. Incidents of polar bear-human conflicts have not increased and those that have occurred cannot be plausibly tied to lack of sea ice (although Derocher and his colleagues have tried) (Crockford 2019, 2020, 2021).
What went wrong?
The experts failed to account for the fact that less summer ice means more primary productivity and therefore, more food for seals and therefore, more food for bears (Coupel and Devred 2019; Crockford 2021; Frey et al. 2020; George et al. 2020). They failed to account for the explosion of harp seal numbers in Davis Strait (DFO 2020; Peacock et al 2013).
They also pretended that abundant summer sea ice for hunting seals was essential for polar bear health and survival when they knew that spring was really the critical feeding period.
In addition, many bears in Hudson Bay and elsewhere have shown a preference for remaining on summer ice of considerably less than 50% concentration, contradicting all of their model assumptions. And lastly, they discounted the feeding opportunities presented by newly-formed shorefast ice in fall.
In short, their mantra that ‘sea ice loss = polar bear decline’ has not been supported by the data they have collected, even though they spin the results as much as possible to make it appear otherwise: the contradictions in localized sea ice declines vs. polar bear health have been too blatantly obvious to cover up.
Bottom line
We are still waiting to see 2/3 of the world’s polar bears disappear due to dramatically low summer ice levels.
References
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