Week before last, temperatures in International Falls Minnesota reached 46 degrees below zero and that was the air temperature, without the windchill. An Arctic blast of cold air broke free from its northern moorings and spread rapidly into Minnesota and nearby states. At those temperatures, breathing through your nose is a challenge, as ice crystals form within the nasal cavity and you quickly find it best to breathe through a scarf or some other device, like a face mask that quickly gets warmed by your breath. But in time, even these filters develop ice crystals and breathing through them can become more labored. Most Minnesotans know what to do under these conditions–they go outside only when they have to and spend more time indoors. Air hockey anyone?
All humans share a short nasal cavity; sufficient time has not elapsed to see if evolutionary adaptations might arise in Minnesotans, such as a longer nasal cavity that would serve to mitigate nasal ice crystal formation. In response to this dry arctic air that crept into Minnesota week before last, I found myself shuttered inside, thinking about polar bears and the special adaptive features they have developed to make it through winters that actually don’t get a lot colder than what we observed recently in Minnesota (January temperatures in the Arctic get to about 58 degrees below zero, so we truly got a blast of real Arctic air), though they stay that way much longer. Polar bears are insulated by about 4 inches of blubber, lying immediately underneath their skin. They also have a larger head and a longer nasal cavity when compared to Brown bears. The longer nasal cavity is probably better at warming the cold air when breathing through the nostrils and polar bears have an olfactory apparatus that can detect minute odor levels miles away. You have heard of the infrared cameras that one uses to gauge heat loss and identify areas in your home that are losing heat through poor insulation. Well, the polar bear is so well insulated that they are virtually invisible to an infrared camera. They are one of the most efficient animals for heat retention we know of.
Polar bears are the largest land-dwelling carnivores, with males reaching up to 1500 pounds; the largest polar bear on record weighed 2210 pounds. Yet, while they are the dominant predator of the Arctic circle, they are slated for extinction perhaps within the next 50 years. A guaranteed disappearance of a predator at the top of the food chain should bother the Hell of out of all of us, because we are predators at the top the biggest and widest food chain in the world. So if polar bears can disappear with the speed of essentially dimming a switch, why can’t this happen to us just as easily? Well of course, for one thing there are more of us–humans number more than 6 billion and by the middle of this century we are scheduled to reach 9 billion, while polar bears, restricted to the Arctic circle region, number about 20,000 to 25,000; their numbers are already declining while human numbers continue to grow. Then too, we occupy a different niche than polar bears and occupy more temperate zones and insure ourselves an adequate supply of food through agriculture and animal cultivation; most of us don’t have to hunt to eat. In contrast, the polar bears have an established a food chain niche that is critically dependent on the retention of sea ice for foraging. This projected elimination of the species is not because of threats from hunting or factors other than the expected conditions that will be brought about by global climate change and the early seasonal loss of sea ice that polar bears depend on for hunting their primary prey–seals. Persistent sea ice is essential for polar bears to hunt. Normally, the sea ice doesn’t break up until September, at which time polar bears are forced by circumstances to move off the sea ice onto land. In the fall, a pregnant female creates a hibernation den within the snow and enters into a state of semi-hibernation during which time, her cubs are born (2-4) and they feed exclusively on mother’s milk for three to four and a half months.
When a mother polar bear comes out of her winter hibernation, with cubs in tow, she will have lost several hundred of pounds of weight, as she had fattened up before hibernation in order to nurse her cubs that are born during the hibernation period. After the birth of the cubs, but still during the hibernation period, mother’s milk is the exclusive source of nourishment used to feed the cubs. So when she emerges with her cubs in the spring, they are old enough to have some mobility and her first need is to get food to nourish herself and keep producing mile to feed her cubs. It’s as if the termination of the hibernation period brings on a food crisis. Normally, when polar bears emerge from hibernation, the arctic sea ice is still intact, which is far more conducive for catching seals, the main diet of polar bears. Even when the sea ice begins to break up in the summer, large chunks of ice allow polar bears to hunt on the ice when seals break through their holes to breathe. But if the sea ice becomes too thin and breaks up into smaller chunks or disappears altogether, seals are no longer constrained to breathe through the ice and polar bears can no longer hunt efficiently. There are reports of polar bears mating with grizzlies, the result of which is to produce hybrids that are less efficient as swimmers and at greater risk when marginal sea ice conditions appear. So, the earlier that the sea ice melts or breaks up, the greater is the risk for polar bears. Reports of polar bear drownings have already appeared, presumably as a result of too much ice melting and making swimming distances between ice flows too great.
The story behind the threat of polar bear extinction began in 2007 and was provided by a report from the U.S. Geological Survey (USGS), indicating that within 50 years, the shrinking sea ice will leave only a small remnant of polar bear populations on the islands of the Canadian Arctic; those along the Alaskan and Russian coasts, which are the populations most often studied, will all be gone. These reports were provided to Congress; a year later, the polar bear was listed as a threatened species under the Endangered Species Act by the United States Department of the Interior.
The report of 2007 made the news in the Anchorage Daily News (article written by Tom Kizzia, September 8, 2007) and, until recently, nothing had changed to alter these grim projections, based on scientific expectations derived from climate change modeling studies, using what is known as a general circulation model (GCM). Those studies indicated that sufficient carbon dioxide had already accumulated such that a “tipping point” had been reached and nothing could be done to reverse the fate of sea ice in the Arctic as it was shrinking at a much faster rate than earlier models had predicted. In a relatively short time, it was predicted that sea ice would disappear and get broken up earlier and earlier in the year, putting more pressure on polar bears. In these studies, the tipping point concept was based on the idea that ice normally provides a reflection of sunlight and thus returns energy from the surface of the earth, preventing some solar radiation from warming the oceans and land surfaces. But as ice surfaces diminish in area, earth and water surfaces get more sunlight exposure. This phenomenon is referred to as the “albedo” effect; it constitutes a positive feedback from melting ice–the more ice that melts, the more sunlight hits the earth and water surfaces and in turn melts more ice. The ice melt of 2007 was especially worrisome. Thus, USGA report of 2007 suggested that this positive feedback system, had already reached a point that future sea ice would melt, perhaps very rapidly, and eliminate most of the polar bear population within 50 years. According to that report a tipping point had already been reached so that no matter what future reductions in carbon emissions might be achieved, the polar bears were doomed.
The 2007 USGA report was not seriously challenged until a recent article appeared in Nature in December 2010 (volume 468, p. 955-958). This report re-examined the idea of a tipping point for sea ice and the future of polar bears. However, in these new modeling studies, the issue was examined based on the assumption that some reduction in greenhouse gases would take place in the future. Using a similar model to that used to project a poor outcome for polar bears, the paper by Amstrup et al accepted different levels of reductions in green house gases as a basis for generating different models that simulated whether or not a normal sea ice pattern could be retained under these conditions of reduced carbon dioxide emissions. Five different models of reduced carbon emissions were used, including one proposal to keep the carbon dioxide levels the same as those of the year 2000 (Y2K model); other models used different scenarios for reducing the level of carbon emissions. First, this study confirmed the 2007 USGA results, strongly supporting the idea that if nothing is done, most polar bears are either doomed or will have to dramatically change their hunting habits (and are probably poorly equipped to do so). However, with reductions in atmospheric carbon dioxide, the Amstrup modeling studies showed that the sea ice could be retained sufficiently to give safe harbor for polar bears. They did not find a “tipping point” that doomed the polar bears and for that reason alone, the study was very encouraging and carried an obviously reduced doomsday prediction. The December 2010 study is exemplary for several reasons. In addition to giving new hope to the polar bears if humans begin to reduce carbon emissions, the Amstrup paper also demonstrates the power of the internet. In a high impact journal such as Nature, papers are given a relatively small amount of space for a single paper–typically three pages or less for an article. But, because information can be stored on the internet, referred to and linked/downloaded while reading the on-line paper, the so called supplemental material can increase the length of the paper by several fold. The polar bear paper referred to was less than three double-sided printed pages in the magazine, but the supplemental material, which contained additional information on the models used, including more color figures and references, was 26 double-sided pages. A second mode of expansion can be seen in the reference section, where if you click on the section, it expands so that each reference has a “show content” link that takes you to an expanded explanation of the reference that has been quoted, what the reference says and why it may or may not be a source of valid observations and conclusions. In short, the Nature paper just described shows why there are no short papers anymore, particularly on a complex subject and within a high impact journal. Now we have three different levels of readership. First, there’s the casual reader, trying to get the general concept of the article, then there’s the serious reader who evaluates the main figures and can talk somewhat intelligently about the article and then there are the global climate change people and serious polar bear biologists who scour through the main article, all the figures, the material in the supplemental section and the expansion of the references, a sort of “why did I use this reference” section. The take home message of all this complexity is that first and foremost, the best and worst case for the future of our polar bears are both based on models–that is all we have to go on. But, increasingly, the models are fed by better and better data and such models are trying to reach down and resolve time limits not achieved in previous work. Instead of centuries long outcomes, models are getting down to half-century and even decades of time. We will see some of these changes within a single human lifetime. But, a single year of weather means nothing–the variables making up our annual weather patterns are too great to project our future from the weather that unfolds in a single season, tempting though it may be to project them forward in time. I seriously doubt that humans have the capacity to remember and log the long-term weather patterns, such that we can become reliable reporters of weather patterns that change over decades: most of us can’t really remember with certainty the weather events of last year. We remember really tough winters and hot summers and there is a sense that we are moving towards warmer conditions, but these transitions are not smooth hyperbolic curves we ride on and that’s why, as much as we like to talk about the weather, we rely on measurements to reveal the true weather trends. Those measurements show, that as the carbon dioxide emissions have increased, the air temperatures are rising, our oceans are warming and expanding, the ice masses are receding and species are threatened. Globally, 25% of mammalian species are threatened with extinction. Habitat loss is the main reason and for the polar bears, the threat of loss of sea ice is also a case of habitat loss, even though it is first and foremost attributed to global climate change and humanoid activity.
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