What’s a good analogy for sea ice as essential polar bear habitat? Biologist Andrew Derocher claims that the soil in a forest is appropriate because without the soil you can’t have the forest ecosystem.
However, that’s a specious comparison because the amount of soil in a forest does not change markedly with the seasons the way that Arctic sea ice does.
A much better analogy is a big pond that dries up a bit every summer. The amount of habitat available to sustain aquatic plants, amphibians and insects is reduced in the dry season but many species have special adaptations for surviving reduced water availability.
For the rest of the year, however, the pond provides an abundant and non-limiting habitat for all the creatures and plants that live there.
One way to think of sea ice is that it's akin to soil in a forest. Take away the soil & you can't have the forest. Sea ice is an integral part of the ecosystem. #polarbears rely on food chain that starts with sea ice algae. No ice, no bears. https://t.co/7OD0GvCJ0Y
— Andrew Derocher (@AEDerocher) October 12, 2018
Insightful graphic of #polarbear habitat loss (or at least that's one view). We're restructuring a whole ecosystem. Sea ice is to the Arctic what soil is to the forest. Without sea ice we'll still have an ecosystem but it won't include polar bears & many other species. https://t.co/XeDx1z6rXn
— Andrew Derocher (@AEDerocher) October 30, 2018
Derocher’s favorite meme is “no ice, no bears” — as if there is a real possibility that sea ice is on course to disappear completely, even in winter.
But that’s nonsense: even during past Interglacial periods that were much warmer than today, there was extensive sea ice in the winter and spring (Stein et al. 2017) and no Arctic species went extinct, even with much less summer sea ice than we have today.
Cronin and Cronin (2015) stated (my bold):
“Despite the scale, frequency and rapidity of Quaternary climate changes, Arctic marine ecosystems associated with sea-ice habitats were extremely resilient, adapting through geographic range expansion into the Arctic during warm periods, and south into extra-Arctic regions during glacial periods. The stratigraphic record of the last 1.5 Ma indicates that no marine species’ extinction events occurred despite major climate oscillations.”
Even the most pessimistic models that predict sea ice changes over the coming decades suggest that winter and spring sea ice will persist at the end of this century (ACIA 2005; AMAP 2017; Durner et al. 2009; Tremblay and Huard 2014; Wang and Overland 2012).
Most importantly, sea ice is necessary for polar bears only from late fall to late spring only — beyond that, sea ice is optional.
Reduced sea ice extent from early summer through mid-fall has had little effect on the health or survival of bears that have had ample food available in the spring (Crockford 2017; Crockford and Geist 2017).
Bottom line: Any discussion of an “ice-free Arctic” refers to summer ice extent only. Arctic sea ice as an ecosystem is not in any danger of disappearing, despite Derocher’s hand-waving.
Sea ice that fluctuates seasonally as a habitat for polar bears is nothing like the soil necessary to sustain a forest every day of every year.
Read more at Polar Bear Science
