The Great White Bear (26 page)

The audience was captive and sympathetic. Buchanan could address his congregation without fear of contradiction or need for explication. Those assembled understood his meaning and nodded sagely and sadly in agreement.

"I want you to do me a favor," he continued. "When you're out there tomorrow" (and here he nodded over his shoulder and out the window of the buffeted buggy to the tempestuous tundra outside) "and you look at a polar bear..."

"If we see one!" interjected one of the small crowd good-naturedly;
it had not been a successful couple of days for polar bear viewing, and buggy drivers had been reduced to feigning enthusiasm for sightings of ptarmigans and arctic hares.

Buchanan pivoted to provide sympathetic explanation—"The problem is, when the weather's like this, the bears tuck themselves in the willows and stick their big butts out to protect themselves against the wind"—before returning swiftly to his theme.

"When you're out there tomorrow, do me a favor," he repeated. "Look at a polar bear and close your eyes, just for a second, and imagine if we are the last generation to see a polar bear. We can't allow that to happen. We just can't."

The call from the lodge that dinner was ready arrived on cue, Buchanan's words lingering in the air for a second before they were replaced by the sounds of zippers and Velcro fasteners as the assembly readied itself for the brief return journey. The small crowd made its way, one at a time forcing the door into the resistant wind, which announced its presence with an angry, high-pitched howl.

On one level, warm is relative. Cold is a matter of opinion.

To the visitors who shrank into their thick coats as they hustled out of Buggy One and back into the Tundra Buggy Lodge, there was no question. The fierce wind that roared off Hudson Bay was probing for any kind of entrance, any opening that would enable it to slice into exposed or inadequately insulated flesh. Its aggressive onslaught served only to exacerbate the ambient temperature, which nudged slowly downward with each passing day.

It was cold.

But for the polar bears that lay just out of sight, the wind carried a different message. Wrapped in protective layers of blubber and fur, built for comfort in the coldest of conditions, they huddled in the willows, their large rumps turned protectively outward. Hunger pangs were building, the need to hunt was growing, and the wind, far from chilling them to their ursine bones, served only to remind them with its relative mildness that the sea ice they depend on had yet to arrive.

It was warm.

But there is, of course, a more objective measure, and while weather may change from hour to hour and day to day—the mercury falling then rising, the wind rising then falling—over longer time periods, studies of temperature and climate can reveal a bigger picture. And as Buchanan had alluded to, and his visitors understood all too well, as cold as it may have felt to them at this particular time on this particular day, that bigger picture showed the emergence over the past several decades of an unmistakable trend.

The planet generally, the Arctic particularly, and Hudson Bay specifically were growing warmer.

Earth's climate is not, and never has been, constant. It varies from decade to decade, millennium to millennium, eon to eon.

From about 750 to about 580 million years ago, for example, Earth, it seems, was all but covered with glaciers, a phenomenon referred to by some scientists as Snowball Earth. At the other end of the spectrum, from approximately 250 million years ago to roughly 50 million years ago, the planet was considerably warmer than today; on either side of the extinction event that spelled the demise of the dinosaurs, average temperatures were as much as 9°F above contemporary averages.

At various points in its history, from relatively recently to hundreds of millions of years in the past, Earth's climate has been affected to varying degrees and in varying lengths of time by a suite of factors. Volcanic eruptions, if of sufficient quantity or ferocity, can slightly reduce the amount of solar radiation reaching the planet's surface, bringing about a degree (in the metaphorical, not literal, sense) of cooling for a number of years or even decades. Earth's orbit is slightly elongated rather than perfectly circular, its axis rotates around an imaginary centerline, and its tilt goes up and down, and all three shift on regular cycles; an intersection of two of these—its tilt and its axis—combined to flood the Northern Hemisphere with solar energy around 15,000 years ago and bring an end to the last Ice Age.

But the most consistent factor in Earth's climate warming or cooling is the composition of its atmospheric gases, a notion that was first mooted early in the nineteenth century by French scientist Joseph Fourier. He wondered why, given that solar radiation was constantly hitting the surface of Earth, the planet didn't keep heating up and ultimately become as hot as the star it orbited. The obvious answer, he concluded, was that energy was being radiated back out to space; but when he worked out the arithmetic, the answer to his equations was an Earth that was below freezing. The explanation, he surmised, was that the atmosphere was trapping some of that heat—as if, he said, the planet were a box covered by a pane of glass, through which, as in a greenhouse, sunlight could enter but heat did not escape.

In 1859, British scientist John Tyndall sought to identify which of the gases in the atmosphere would be most likely to perform such a feat. Through a series of tests in his laboratory, he determined that the atmosphere's primary constituents, oxygen and nitrogen, were transparent to the sun's infrared radiation and thus not a factor. Methane, however, was, as Spencer Weart describes it in
The Discovery of Global Warming,
"as opaque as a plank of wood"; so, too, was a gas of seemingly little consequence in the atmosphere, carbon dioxide. It seemed unlikely that carbon dioxide on its own could have much impact on temperatures, reasoned Tyndall, because it constituted such a small percentage of atmospheric gases. Of likely greater import, he proposed, was water vapor, which is a more voluminous greenhouse gas and which, Tyndall poetically declared, "is a blanket more necessary to the vegetable life of England than clothing is to man."

Thirty-seven years later, Swedish scientist Svante Arrhenius realized that a small increase in carbon dioxide might warm up the atmosphere sufficiently to allow it to hold more water vapor—which would in turn lead to further warming. Arrhenius also recognized that such increases in carbon dioxide levels could result from industrial processes, specifically the burning of fossil fuels such as coal and oil. Because those fuels contain carbon, their combustion returns carbon to the atmosphere, where it combines with oxygen to create CO
₂
. At the time, the amount of carbon that had been released was, he calculated, insufficient to make much difference; but, he reckoned, were the amount of CO
₂
in the atmosphere to double, global temperatures could increase by as much as 8°F to 9°F. Based on the emission rate at the time, he estimated that such an eventuality would not unfold for at least two thousand years. A little more than a century later, his calculations are being put to the test far more rapidly than he imagined.

Scientists employ a number of devices to measure past climate and atmospheric conditions. Because, absent the invention of a time machine, these conditions must be inferred, the evidence on which they rely is called proxy data. Those can include anything from historical records—such as diaries and ships' logs—to the distribution of fossil corals and the rings in trees. Of particular value, however, in determining levels of atmospheric carbon dioxide up to 800,000 or so years into the past are ice cores, cylindrical samples gathered by drilling deep into the Greenland and Antarctic ice sheets, where thousands upon thousands of tiny air bubbles have collected over the eons, perfect snapshots of past atmospheric composition.

By analyzing such ice cores, researchers have been able to determine that during the last Ice Age, levels of CO
₂
in the atmosphere were approximately 200 parts per million (ppm). In preindustrial times, those levels were closer to 285 ppm. Since the middle of the eighteenth century, however, and the dawn of the Industrial Revolution, those levels have grown, steadily at first and then with increasing rapidity. In 1958, the first year of a continuous measurement of atmospheric CO
₂
levels from Mauna Loa in Hawaii, that figure had climbed above 310 ppm. It has increased since, and at the time of this writing, in late 2009, it is close to 390 ppm. The difference between now and the period before the Industrial Revolution, in other words, is greater than the difference between immediately preindustrial times and the Ice Age.

As a consequence, according to the Intergovernmental Panel on Climate Change (IPCC), global temperature has increased by an average of 1.3°F over the past century, and average Northern Hemisphere temperatures during the second half of the twentieth century were very likely greater than in any 50-year period over the past 500, and quite possibly the last 1,300, years. And global temperatures are continuing to climb, ever more steeply: the 1980s were the hottest decade on record, until the 1990s, which were, on average .25°F warmer. The first decade of the twenty-first century was warmer still—.36°F warmer than the nineties.

The warming that has taken place, and that which is predicted to, has not been and will not be uniform. Some areas—parts of the southeastern United States, for example—have, if anything, experienced a slight cooling. It is possible that feedback mechanisms resulting from, for example, huge influxes of fresh water into the North Atlantic as a consequence of melting of the Greenland ice sheet could disrupt warm water currents and cause western Europe to experience either cooling or at least reduced warming. Equatorial regions are, in general, so far showing relatively little temperature increase. But the regions of the world where warming is already most measurable and extreme, where impacts are already noticeable and are predicted to advance most rapidly, are at the ends of the Earth, in the Antarctic and, especially, the Arctic.

Although here, too, there has been regional variation
^*
—Alaska and Siberia, for example, appear to be warming more rapidly than Greenland—average annual temperatures in the Arctic have increased by approximately 0.75°F since the mid-1960s—more than four times the rate for the globe as a whole and enough for a recent study to conclude that the Arctic is warmer now than it has been for at least two thousand years.

There are several reasons why the Arctic should be at the forefront of global warming. The "weather layer" of the atmosphere known as the troposphere is thinner above the Arctic than over the equator; as a consequence, it takes less energy to create a given amount of warming. In tropical regions, where the air is already warmer and thus more humid, a greater proportion of the sun's energy is expended on evaporation; the drier air of the Arctic offers no such obstacles and so that energy leads directly to heating.

And once the heating begins, it feeds on itself, more heating causing more heating until eventually the cycle is in danger of becoming unstoppable. To understand why, once the Arctic begins warming, it is increasingly and ultimately irresistibly vulnerable to further warming, we must look to the very thing that helps define it, that is both a consequence and facilitator of its normal frigid state.

The white shroud that characterizes polar regions descended upon them because their lower temperatures enabled it to. And then it helped perpetuate those temperatures because ice and snow reflect sunlight back into space, a phenomenon known as albedo. But as the ice begins to melt, the darker land and ocean that emerge from beneath absorb, instead of reflect, the sun's energy. (Whereas ice
reflects
as much as 90 percent of the solar radiation that strikes it, for example, the surface of the ocean
absorbs
a similar percentage.) In the Antarctic, the greatest contributor by far to the albedo effect is the giant ice cap that blankets the continent year-round. At the other end of the globe, surpassing even the Greenland ice sheet, that honor belongs to the sea ice of the Arctic Ocean.
^*

For comparison, we revisit the Antarctic. Unlike its northern cousin, sea ice in the Antarctic is a purely seasonal affair. Extensive in winter but unrestrained by landmasses, in summer it breaks up and drifts away. The Antarctic winter sea ice extent has not shown any appreciable change—if anything, it has shown a slight, if statistically insignificant, increase; in summer, it melts almost in its entirety as it has always done.

But in the northern realms, sea ice is constrained by the boundaries of the landmasses that encircle the Arctic Ocean. With the exception of the Fram Strait east of Greenland and a smaller artery, the Nares Strait, between Greenland and Ellesmere Island, there is no avenue through which sea ice can escape. As a result, while much Arctic sea ice melts each spring and summer, ice floes in the higher latitudes can persist from year to year, traveling around the Arctic Ocean basin, grinding into and on top of each other, becoming thicker and more resistant to melt. Which makes sea ice in the Arctic a much more interesting barometer than that of the Antarctic; under no scenarios as presently imagined would sea ice fail to form in the boreal winter any more than in the austral one. But it stands to reason that, as the Arctic warms, thick ice would become thinner ice as it melts, thinner ice would melt before it has a chance to thicken, the extent and volume of Arctic sea ice would diminish, and the pace of decline would accelerate as temperatures increase and larger areas of heat-absorbing ocean promote further warming.

Which is, it seems, exactly what is happening.

In 1978, NASA launched the Scanning Multichannel Microwave Radiometer (SMMR), which, because it uses microwaves, is able to image the ice cap through clouds and in darkness. Ever since, scientists have been able to map Arctic Ocean sea ice as it contracts and expands, painting a constantly changing picture of its movements and plotting a long-term portrait of its trends. Combined with shipping records and ice charts, those satellite records show unequivocally that Arctic sea ice extent has been declining since at least the 1950s and that, much like the increase in global temperatures that has driven it, that decline has increased sharply in the past decade.