The Great White Bear (28 page)

Stirling discussed all these issues in his 1988 book, but he did not address what now seems a glaring absence, what is in the early years of the twenty-first century the most widely discussed environmental consequence of drilling for oil and burning fossil fuels: its ultimate impact on the global climate and thus, most important in this particular context, on the Arctic sea ice and the species that depend on that sea ice for their survival. That he did not do so is not surprising. The mechanisms by which greenhouse gas emissions might warm the planet had been long established, of course; observations from Mauna Loa had been monitoring an increase in atmospheric carbon dioxide for thirty years; the scientists on the leading edge of the issue, epitomized by but by no means limited to NASA's James Hansen, had begun sounding the alarm, their concerns amplified by a few prescient writers. But climate models were in their relative infancy and, compared to those that were to come, were simplistic representations of toy planets; Hansen himself predicted that the clarity of anthropogenic global warming would only truly emerge from the background statistical noise by the turn of the century. And some writers were less prescient than others: in 1987, for example, a young observer of matters environmental named Kieran Mulvaney devoted approximately ten pages of a fifteen-page book chapter to tropical deforestation and only a couple of paragraphs to the emerging issue of climate change, the possible consequences of which he confessed sounded a little "like science-fiction."

But in the years immediately following his book's publication, Stirling noticed something puzzling. The bears he studied year after year in western Hudson Bay, near Churchill, were declining—not in numbers, necessarily, but in size. Their famously rotund profiles were becoming comparatively skinny. Stirling and graduate student Andrew Derocher, who himself has gone on to become one of the leading lights of what remains a fairly small band of polar bear field biologists, looked at the data, crunched them, reexamined them, looked at them from a different angle, and crunched them again; but however they approached the data, the conclusions were the same. It was a linear, one-way trend, which initially prompted the two researchers to discount climate as a possible factor because, they reasoned, something with such annual variability could not account for such a steady progression. They considered other possible factors—pollution, hunting, other forms of human interaction—before returning to the explanation they had earlier set aside.

The result was the 1993 publication in the journal
Arctic
of a paper entitled "Possible impacts of climate warming on polar bears." The paper did not attempt to make a definitive link between the decreased size of bears in Hudson Bay and any warming in the climate, but Stirling and Derocher did note that, during 1992 when the summer was in fact anomalously
colder
than the mean average—likely because of the effects of the eruption of Mount Pinatubo in the Philippines—sea ice cover on Hudson Bay lasted an extra three to four weeks, and the bears not only took advantage of every extra day, they accordingly returned to land for their summer fast fatter than they had been for some years. This suggested, they wrote, "that polar bears remain on the sea ice hunting seals for as long as possible," and that therefore, conversely, diminished time on the ice as a result of the ice breaking up earlier in summer or forming later in fall could have an opposite, deleterious effect. Starting with a formulation by a different researcher that an increase of just under 1°F in average temperature in the Hudson Bay region (significantly less than models predicted for northern Canada) might be sufficient to cause the ice to break up one week earlier in western Hudson Bay and two weeks earlier in the bay's eastern region, Stirling and Derocher calculated a dietary intake for an average female polar bear, as well as the amount of fat burned during the summer fasting period. They concluded that, if ice broke up one week earlier and refroze one week later, a female bear in Hudson Bay would return to the ice on average about 48.5 pounds lighter. Were that to be the case, they wrote, "fewer adult female polar bears would be able to store enough body fat to produce and successfully wean cubs. Eventually, cub production would not balance mortality and the population would decline. Furthermore, it is likely that females that were successful at raising cubs to the fall would be unable to nurse them through the ice-free period because of being unable to store adequate fat reserves."

The paper's summary was groundbreaking in its conclusion:

If climatic warming occurs, the first impacts on polar bears will be felt at the southern limits of their distribution, such as in James and Hudson bays, where the whole population is already forced to fast for approximately four months when the sea ice melts during the summer ... Early signs of impact will include declining body condition, lowered reproductive rates, reduced survival of cubs, and an increase in polar bear—human interactions ... In the High Arctic, a decrease in ice cover may stimulate an initial increase in biological productivity. Eventually however, it is likely that seal populations will decline wherever the quality and availability of breeding habitat are reduced ... Should the Arctic Ocean become seasonally ice free for a long enough period, it is likely polar bears would become extirpated from at least the southern part of their range.

Six years later, Stirling, writing now with Nick Lunn and John Iacozza, published another paper in
Arctic.
The tone this time was stronger. The additional years of observation had provided the researchers with the confidence to move beyond the purely speculative and theoretical.

"From 1981 through 1998, the condition of adult male and female polar bears has declined significantly in western Hudson Bay, as have natality
^*
and the proportion of yearling cubs caught during the open water period that were independent at the time of capture," they wrote. Over this same period, they continued, the breakup of the sea ice on western Hudson Bay had been occurring earlier; each year, the earlier the ice broke up, the poorer the condition of the bears as they came to shore. They concluded: "The trend toward earlier breakup was also correlated with rising spring air temperatures over the study area from 1950 to 1990 ... The ultimate factor responsible for the earlier breakup in western Hudson Bay appears to be a long-term warming trend in April—June atmospheric temperatures."

By now, climate change had moved to the front burner scientifically and politically; the signing of the United Nations Framework Convention on Climate Change in 1992 and the addition of the Kyoto Protocol in 1997, which established mandatory limits for greenhouse gas emissions, marked the first tentative forays into international cooperation to address global warming. The formation in 1988 of the Intergovernmental Panel on Climate Change (IPCC) created an international scientific exchange and repository and kick-started a series of approximately five-yearly assessment reports, each updating the one before and each providing the most comprehensive consensus summary of climate-related observations and predictions available at the time.

Regionally, a scientific symposium in Reykjavik, Iceland, in November 2004 saw the presentation of the results of the Arctic Climate Impacts Assessment (ACIA), which were made available, publicly and gratis, in a 140-page synthesis report entitled
Impacts of a Warming Arctic.
The report acknowledged that "Earth's climate is changing," that "these climate changes are being experienced particularly intensely in the Arctic," and that, among the impacts of such changes, "reduction in sea ice is very likely to have devastating consequences for polar bears, ice-dependent seals, and local people for whom these animals are a primary food source." In a press release issued at the conclusion of its eleventh meeting, in Copenhagen, Denmark, in 1993, the IUCN Polar Bear Specialist Group referenced publicly for the first time concern "about the possible detrimental effects of climate warming on polar bears." By the time of its thirteenth meeting, in Nuuk, Greenland, in 2001, the group referred to "ecological change in the Arctic as a result of climate change and pollution" as posing one of the "greatest future challenges to conservation of polar bears."

Three years later, Andy Derocher, Ian Stirling, and Nick Lunn published a synthesis of all the available information on likely consequences for polar bears of a changing Arctic, both observational and conjectural.

They affirmed that changes in sea ice extent and the timing of both freeze-up and breakup pose potentially the most significant and fundamental threat to the existence of polar bears throughout their range by reducing the availability and abundance of seals—although, they pointed out, in the short term there is the prospect that climatic warming might improve bear and seal habitats in some areas if thick multiyear ice were replaced by annual ice with more leads. As sea ice thins, they continued, it would become not only more fractured but also, as a consequence, more likely to be at the mercy of ocean currents, ice islands twisting and turning and circling around Arctic waters. And while polar bears routinely wander vast distances across shifting pack ice, ice that moves farther and more rapidly would transform the slowly rotating gyres on which they routinely travel into more swiftly and unpredictably swirling eddies. This would force the bears to work harder against the ice's direction in order to return—as, for all the distance they traverse, they so often do—to the point from which they came. And they'd be required on occasion to navigate ice that is thin and ill suited to supporting the weight of a large carnivore, forcing them at times even into the water, obliging them to swim for longer than they are accustomed. All of this would combine to sap them of energy in an environment in which energy is always at a premium and in which, with their favored prey likely less numerous and less accessible, it would be even more so.

Not all impacts are created equal, and for pregnant females the consequences of a combination of diminishing, more rapidly moving ice and polar bears' inherent fidelity to certain sites could be particularly severe. Wrote the three researchers: "As the distance increases between the southern edge of the pack ice, where some polar bear populations spend the summer, and coastal areas where pregnant females den, it will become progressively more difficult for them to reach their presently preferred locations." A previous study, they noted, had suggested that "by the 2050s, the mean minimum extent of the sea ice in the polar basin would be about 600 km [370 miles] from the north coast of Alaska or western Siberia and 100 or so km [roughly 60 miles] north of Svalbard. Two of the three largest known polar bear denning areas are on Wrangel Island and the Svalbard Archipelago. It seems likely that if this prediction is correct, pregnant females will likely not be able to reach either of these areas." The prognosis was no less bleak for those polar bears that choose to den on sea ice, as do a slight majority of the female bears in the Beaufort Sea region. The anticipated extra fractures in the ice, and the likelihood of floes and ice islands drifting farther and faster, raise the prospect that the distance from core hunting grounds that the dens travel while mother and cubs are inside, already regularly in the order of hundreds of miles, will in the future prove far too great for a newly emerged, undernourished female and two tiny youngsters to navigate.

In the end, they wrote, while all bear species are intelligent and adaptable, polar bears no less than any others, the rapid rate of change in the Arctic and polar bears' highly specialized nature lead to one inescapable conclusion: were sea ice to disappear completely as had been predicted by some, "it is unlikely that polar bears will survive as a species."

There were, and are, dissenters, critics questioning variously whether climate change is indeed occurring, whether Earth is in fact warming, and whether, as a consequence, polar bears are at any greater risk of depletion, extirpation, or extinction than they were, say, fifty years ago. In 2007, a group of authors led by Marcus Dyck argued, among other points, that spring air temperatures in the Hudson Bay region showed no particular increase beyond the expected interannual variation, that any changes in the timing of sea ice breakup in Hudson Bay were not statistically significant, and that the contention that polar bears cannot survive as a species without summer sea ice was dubious. Anyway, if the summers did become especially tough, polar bears could adapt by adopting a hibernative state, like their black and brown bear relatives.

As for observed changes in polar bears' health, they could just as easily be ascribed to other causes. Repeated darting and examination by scientists were surely bound to stress polar bears and quite possibly affect their physical condition—to say nothing of being constantly gawped at by tourists in vehicles that lumber past them on the tundra, or being captured and placed in the Polar Bear Jail every time they wander into Churchill.

But Dyck and his coauthors had not looked at temperatures over the same time period as Stirling and colleagues in their earlier assessment. Instead, they had, for no discernible reason, taken an apparently arbitrary starting point of 1932, which happened to coincide with a brief warm spell, rather than focus on the more recent time period when the biologists had recorded increasing temperatures in the air and decreasing conditions in the bears. Blaming those decreasing conditions on scientists and Tundra Buggy tourists contradicted all the available studies that had investigated those very impacts and also ignored the clear correlation that Stirling and others had shown between bears' physical state and the amount of time they were able to stay on the sea ice. As for the suggestion that polar bears could just learn to hibernate, like their relatives: unfortunately, an inconvenience of evolution is that such physical adaptations tend not to take place overnight, or even within the number of generations that stand to be affected by a rapidly changing climate. Besides, black and brown bears don't truly hibernate, either; as Stirling, Derocher, and others pointed out, "Large mammals are prevented from being true hibernators by the tremendous energetic costs associated with arousal from a low metabolic state"—a cost that would be even greater for the largest carnivore in the coldest environment. Which is why, they continued, the largest hibernating mammals are, in fact, marmots.