In The Arctic Journal, 7 October 2015: Unstable thinking about polar bear habitat [not my title choice]
This is a previously unpublished summary, written exclusively for The Arctic Journal, of my peer-reviewed, fully referenced essay on this topic that was published earlier this year by the Global Warming Policy Foundation in their “Briefing Paper” series (#16, June 8, 2015: The Arctic Fallacy: Sea Ice Stability and the Polar Bear), which includes a foreword by Dr. Matthew Cronin, Professor of Animal Genetics at the University of Alaska Fairbanks. Pdf here.
Here are the essential points, one by one:
• Wide variations in spring sea ice habitat are a natural phenomenon and occur independently of any summer sea ice changes that may be due to human-caused global warming.
• Fast ice, where many ringed seals have their pups, can get extremely thick during especially cold winters.
• Strong winds can also drive sea ice onshore, as happens about every 10 years or so off Eastern Alaska and the Northwest Territories of Canada, leaving buckled ice that is too thick in most places for ringed seal breathing holes and birthing lairs, so they move elsewhere; polar bear females emerging from onshore dens with new cubs find no newborn ringed seals to eat, so the tiny cubs die from starvation (as do young bears on their own for the first time).
• Deep snow over sea ice in spring can effectively hide ringed seal birth lairs from hungry polar bears when they need abundant food the most, so many cubs die and adult females may not be able to eat enough to maintain a pregnancy the following year.
• Spring sea ice thickness has been naturally variable over time scales of a few years to decades in the Beaufort Sea, East Greenland, and Hudson Bay; spring snow depth on sea ice is known to vary over short periods – all with devastating effects on local polar bear populations.
• For example, the last time that thick spring ice conditions developed in the Beaufort Sea (2004-2006), biologists estimated the local population dropped 25-50%; similar conditions in 1974-1976 were described as equally devastating.
• Conditions in spring (April- June) are critical because it is the period of on-ice birth, nursing, and mating for ringed seals and is also when polar bears consume two-thirds of their annual prey and seek their mates.
• None of these naturally devastating effects of thick spring ice are included in models that forecast the future for polar bear populations, which model only summer ice changes.
• Biologists now attribute virtually every downturn in population size of polar bears to declines in summer sea ice blamed on human use of fossil fuels: they have shifted the blame for the devastation caused by thick spring ice or heavy snow onto recent summer ice declines, allowing them to claim that summer ice changes are manifestations of unprecedented, human-caused habitat instability.
• The assumption that Arctic sea ice is a naturally stable habitat over short time frames is a biological fallacy: predictive population models based on this myth are flawed, their results illusory because they do not take critical spring sea ice changes into account.
• However, the International Union for the Conservation of Nature (IUCN) and the US government have, for the first time, accepted modeled (future) population declines of Arctic species based on modeled (future) summer sea ice changes as valid threats to their survival, all built upon this fallacy.
Given what we now know about the animals and their naturally changing habitat, it is time to concede that existing data do not support predictions that polar bears are threatened with extinction due to summer habitat instability.
Here is the full paper:
Crockford, S.J. 2015. “The Arctic Fallacy: sea ice stability and the polar bear.” GWPF Briefing 16. The Global Warming Policy Foundation, London. Pdf here.