Thawing out the Polar Bear: Global Warming and Arctic Canada - Essay Example

Your Your Thawing out the Polar Bear: Global Warming and Arctic Canada As long as there have beenpolar bears, they have traveled and hunted on floating sea ice. One of the most dramatic, and most consistently documented phenomena of global warming has been the breaking up of ice in the Arctic. As this continues, the life of the polar bear will be significantly affected (Stirling and Derocher, p. 242). While most polar bears use land-based habitats for maternity denning, and while some retreat to land in places where the sea ice melts altogether in the summer, these changes will still affect the species as a whole. In particular, the higher-latitude populations, like those in the Beaufort and Chukchi seas, only retreat to the multiyear ice on the polar basin during the summers. For food, polar bears enjoy phocid seals, as well as bearded seals (Smith, p. 2205) as their primary sources, although other varieties of seals, as well as walruses, will also do. Just about all of the Arctic Ocean around the North Pole has served as a suitable habitat for the polar bear. Recent estimates of the polar bear population range between 21,500 and 25,000 (IUCN/SSC Polar Bear Specialist Group, p. 26). The primary threat in years past to the polar bear population has been overharvesting, but recent measures have been instituted to correct this trend (Prestrud and Stirling, p. 116). Because of the location of the habitats, the impact of human development has been minimal, and so the polar bear has maintained a high percentage of its original range, especially in comparison to other large carnivores. However, it is fairly clear that the effects of melting polar ice due to global warming will be far more invasive to the polar bears’ habitats (Derocher). There is a considerable body of research supporting the existence of global warming in the Arctic, and also supporting that the rate of global warming may accelerate from its present levels (Serreze e.a., Parkinson and Cavalieri, Comiso). Time has adapted most of the mammals indigenous to the Arctic marine ecosystem to the environment of sea ice; in fact, it has become crucial for pagophilic (“ice-loving”) mammals and epontic marine communities, with the result that if ice continues to disappear from some parts of the Arctic region, the ecosystem will alter drastically. Specific effects could include the loss of life in the continental shelf under the ice, reductions in total sea ice area as well as in the duration of sea ice lasting during the year, thinner ice, changed snow cover, and increased ice drift (Derocher). Scientists have documented the considerable effects that climate can have on the life history patterns of animals (Stearns, p. 102). While these effects can at times be cyclical, in response to long-term patterns in climate, the primary concern about the contemporary trend for global warming is that it will not be cyclical, but will instead increase without stopping (Derocher). There are a number of ways that this warming could affect polar bears in Arctic Canada and throughout the polar region, and there are a number of approaches to figuring out just what these effects will be, and how severe they will be. The most unique characteristic of the polar bear is the fact that it is pagophilic. It evolved from the brown bear and moved into the large, fertile, but mostly vacant opportunity for a large predator (Stirling and Derocher, p. 244). Despite the fact that females will return to land to bear and care for their young, the polar bear depends on what is found on the sea ice for sustenance, and so will be profoundly affected by major changes to the sea ice habitat (Derocher). Of the different kinds of sea ice, polar bears tend to prefer the annual variety that forms over the continental shelf and the archipelagos that surround the polar basin. In recent years, the total sea ice has declined, near shore areas as well as in the multiyear ice layers (Parkinson and Cavalieri, Comiso). The reason for these changes has been identified as climatic warming, a trend that no current models predict will stop, or slow, in the near future. The most obvious symptom of the global warming problem is the decrease in both the distribution area and the total abundance of annual and multiyear ice (Maslanik e.a.). Since 1978, total ice cover has declined by 14% (Vinnikov e.a., p. 1935). Comiso has reported, additionally, that the 20-year trend for surface temperature data is eight times greater than the 100-year trend, which would suggest that warming has accelerated rapidly in more recent years. Comiso also predicts that by the year 2050, except for Greenland and the farthest north parts of the Canadian Arctic Archipelago, the remaining ice will not lie on the continental shelf but on the deeper waters in the polar basin. In such areas as Hudson Bay, the ice might even be gone by 2050 (Gough and Wolfe, p. 144). It is not just the annual ice that is at risk, however. Comiso also reported that the perennial sea ice cover in the Arctic declines at a rate of approximately 9% per decade, and may be gone by the year 2100. Currently, one of the main features of the Sverdrup Basin in the Canadian High Arctic Archipelago is the expansive multiyear ice. However, Melling noted a heat flux originating in the Atlantic that is affecting the Sverdrup Basin waters, which could easily result in the deterioration of a currently stable network of ice bridges. While the research is diverse in its predictions as to the rate of global warming, the fact that all of the research agrees that the global warming trend will continue is a sobering one. The consensus of the research appears to indicate that the climate is warming, that total ice cover is disappearing quickly, and that there are large areas in the polar basin that may have no ice in no more than 100 years. These findings do not even begin to take into account changes in greenhouse gases, or the effects of increased precipitation on the ice, which may be an effect of the warming planet (Derocher). As changes occur over time, the first to be noticed could well be the earlier breakup of annual ice each year. While these might first be documented farther south than the Canadian Arctic, that has not yet been made a certainty. Polar bears have an annual cycle of storing adipose tissue when the hunting is going well, and then using that adipose tissue for sustenance when times are lean (Watts and Hansen, p. 308). Studies have shown that there has been considerable variation in reproductive output and body size over shorter periods (2-3 years) and longer periods (10+ years), depending on the conditions of the ice (Kingsley, p. 1022). In western Hudson Bay, for example, the annual ice breaks up about 2 ½ weeks earlier each year than it did 30 years ago (Stirling and Derocher, p. 243). The result of this is less time that bears can feed on seals in the late spring and early summer. This reduction in time means that the periods when the polar bears cannot feed will be longer. Body size will decrease; reproductive output will decrease; survival of the young will decrease (Derocher). Some specific data has been collected to support these predictions. Adult polar bears lose about 0.9 kg of body mass each day during the fasting period (Stirling and Derocher, p. 242). In 1982-1990, the mean mass of pregnant females in the autumn in western Hudson Bay was 283 kg, and the minimum mass at which successful reproduction occurred was 189 kg (Derocher). Over time, if the sea ice period shortens by ½ a day each year, most female polar bears in western Hudson Bay will be unable to maintain sufficient body mass to reproduce in about 100 years. Interestingly, though, more recent projections show a larger loss of body mass on an annual basis for female polar bears; the average female lost 4.71 kg each year. Based on those numbers, a linear projection would show that most females in the region would be unable to reproduce successfully after 2012 (Stirling and Derocher, p. 241). The changes in body mass are not the only effects that global warming will have on female reproduction in the polar bear population of Arctic Canada. Female polar bears tend to pick particular den areas and stick with them; they generally choose sites that are on land, within a few kilometers of the coast (Schweinsburg, p. 169). For this to work, though, the ice has to either drift or freeze early enough to give the females time to get to land and dig a den; this usually happens in late October to early November. As the southern edge of the pack ice, where the polar bears spend the summer, gets farther away from the coastal areas where the denning takes place, it will be harder for the females to get to the places they have chosen. Comiso has predicted that this distance will double by 2050, making it impossible for the females to reach their chosen coastal areas in time to den and give birth. While successful denning has been recorded on ice floes, this practice will require females and small cubs to travel much farther to return to their normal home range. One could speculate that cubs will tend to have a higher mortality rate as their travel increases, and it is not known how efficiently the polar bears will adapt to having to build dens on the drifting pack ice (Derocher). Additionally, treadmill studies have shown that polar bears exert a great deal more energy walking than one might expect by extrapolating from general equations for all mammals. Also, polar bears only reach their maximum walking efficiency as adults (Hurst e.a., p. 394). As a result, increasing these travel distances will also increase the polar bears’ need to store up energy during the feeding seasons. This stored-up energy has already been placed at risk by shortening the feeding seasons, and so polar bears face a double-edged threat at the hands of global warming. Because it takes polar bears so long to learn to walk efficiently, the burden of the increased need for energy will be even greater on the young polar bears, even further endangering their chances for long-term survival. Another threat to the supply of energy for polar bears has to do with the availability of prey. If areas beneath the sea’s surface began to vary in biological productivity, then so will the distribution of seals throughout the area. As the seals go, so go the polar bears, and so a crucial factor for the polar bear population will be the accessibility of prey species in the changed sea environment. As open water becomes more available, the hunting efficiency of polar bears may well decrease, because the seals will have fewer restrictions in their access to air, and will not need to maintain breathing holes and haul-out sites, making them less predictable to the polar bears. It is extremely rare for a polar bear to capture a seal in open water, and it is also unlikely that open-water hunting will compensate for the loss of ice (Derocher). As the number of kills declines, this could have a trickle-down effect for the young of the species. Generally, polar bears prefer to feed on the blubber of their prey, and adults tend to leave a great deal of the protein behind (Stirling and Derocher, p. 243). Young bears have not developed their killing skills as efficiently, and often depend on the leftovers from adult kills for their sustenance. If the number of kills goes down, the adult bears may eat more of each kill to make up for the difference, leaving less food behind for the young to consume (Derocher). Another by-product of global warming that will be more difficult to predict could be an increase in human-polar bear interactions. A study in Churchill, Manitoba, showed that in years when the annual ice broke up earlier, there were more cases of problem bears coming into town and being dealt with by Conservation Officers than in years when the breakup happened later (Derocher). In the Beaufort Sea, after the heavy ice winter of 1974, which caused the numbers of ringed seals to decrease significantly, bears were observed to be significantly thinner, and two humans were killed and eaten by starving bears (Kingsley, p. 1024). Given the fact that the highest concentrations of the polar bear population are in areas far from significant concentrations of the human population, however, this is a trend that could take a long time to be noticeable or important. In conclusion, there are several elements of the situation that are worth noticing. Clearly, the polar bear population in Arctic Canada depends on the ice in a number of ways. It is their habitat during the summer months; it restricts the ringed seals’ access to air, giving the polar bears a way to predict when and where the seals will come out to the surface, so that the bears can hunt and kill the seals. It is also the females’ mode of transportation to their preferred places to build dens and give birth to their young. Even if we ignore, momentarily, the effects that the melting of the polar ice will have on the rest of the world (rising tides, large parts of the current coastlines of the world being totally submerged), this trend appears poised to radically alter life for the thousands of polar bears in the Arctic region. There are two points in the research that should be particularly frightening to the environmentally concerned. First, the science is unanimous in its prediction of continued global warming. Second, the rate of global warming is still unknown, but the recent, or 20-year, data seems to show a faster rate of increase than the longer-term, or 100-year, data. This could mean that whatever changes are coming for the global environment could start coming even earlier than had been projected. The results for Arctic Canada, and all of its biological life, could well be disastrous. Works Cited Comiso, J. C. “Correlation and trend studies of the sea-ice cover and surface temperatures in the Arctic.” Annals of Glaciology. 34:420-428. Derocher, A. E. “Polar Bears in a Warming Climate.” Integrative and Comparative Biology, April 2004. Accessed 20 March 2007 online at http://www.findarticles.com/p/articles/mi_qa4054/is_200404/ai_n9356419. Gough, W. A. and E. Wolfe. “Climate change scenarios for Hudson Bay, Canada, from general circulation models.” Arctic 54:142-148. Hurst, R. J., N. A. Øritsland, and P. D. 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Derocher. “Possible impacts of climatic warming on polar bears.” Arctic 46:240-245. Vinnikov, K. V, A. Roboek, R. J. Stouffer, J. E. Walsh, C. L. Parkinson, D. J. Cavalieri, J. F. B. Mitchell, D. Garrett, and V. F Zakharov. “Global warming and northern hemisphere ice extent.” Science 286:1934-1937. Watts, P. D. and S. E. Hansen. “Cyclic starvation as a reproductive strategy in the polar bear.” Symposium of the Zoological Society of London 57: 305-318. Read More