Field Notes From a Catastrophe: Man, Nature, and Climate Change (4 page)

At the time the
Des Groseilliers
set off, little information on trends in sea-ice depth was available. A few years later, a limited amount of data on this topic—gathered, for rather different purposes, by nuclear submarines—was declassified. It showed that between the 1960s and the 1990s, sea-ice depth in a large section of the Arctic Ocean declined by nearly 40 percent.

Eventually, the researchers on board the
Des Groseilliers
decided that they would just have to settle for the best ice floe they could find. They picked one that stretched over some thirty square miles. In some spots it was six feet thick, in some spots just three. Tents were set up on the floe to house experiments, and a safety protocol was established: anyone venturing out onto the ice had to travel with a buddy and a radio. (Many also carried a gun, in case of polar-bear problems.) Some of the scientists speculated that, since the ice was abnormally thin, it would grow thicker during the expedition. Just the opposite turned out to be the case. The
Des Groseilliers
spent twelve months frozen into the floe, and, during that time, it drifted some three hundred miles north. Nevertheless, at the end of the year, the average thickness of the ice had declined, in some spots by as much as a third. By August 1998, so many of the scientists had fallen through that a new requirement was added to the protocol: anyone who set foot off the ship had to wear a life jacket.

The extent of the Arctic’s perennial sea ice has declined dramatically in recent years. Credit: F. Fetterer and K. Knowles,
Sea Ice Index,
National Snow and Ice Data Center.

Donald Perovich has studied sea ice for thirty years, and on a rainy day not long after I got back from Dead horse, I went to visit him at his office in Hanover, New Hampshire. Perovich works for the Cold Regions Research and Engineering Laboratory, or CRREL (pronounced “crell”). CRREL is a division of the U.S. Army that was established in 1961 in anticipation of a very cold war. (The assumption was that if the Soviets invaded, they would probably do so from the north.) He is a tall man with black hair, very black eyebrows, and an earnest manner. His office is decorated with photographs from the
Des Groseilliers
expedition, for which he served as the lead scientist; there are shots of the ship, the tents, and, if you look closely enough, the bears. One grainy-looking photo shows someone dressed up as Santa Claus, celebrating Christmas in the darkness out on the ice. “The most fun you could ever have” was how Perovich described the expedition to me.

Perovich’s particular area of expertise, in the words of his CRREL biography, is “the interaction of solar radiation with sea ice.” During the
Des Groseilliers
expedition, Perovich spent most of his time monitoring conditions on the floe using a device known as a spectroradiometer. Facing toward the sun, a spectroradiometer measures incident light, and facing toward earth, it measures reflected light. By dividing the latter by the former, you get a quantity known as albedo. (The term comes from the Latin word for “whiteness.”) During April and May, when conditions on the floe were relatively stable, Perovich took measurements with his spectroradiometer once a week, and during June, July, and August, when they were changing more rapidly, he took measurements every other day. The arrangement allowed him to plot exactly how the albedo varied as the snow on top of the ice turned to slush, and then the slush became puddles, and, finally, some of the puddles melted through to the water below.

An ideal white surface, which reflected all the light that shone on it, would have an albedo of one, and an ideal black surface, which absorbed all the light, would have an albedo of zero. The albedo of the earth, in aggregate, is 0.3, meaning that a little less than a third of the sunlight that strikes it is reflected back out. Anything that changes the earth’s albedo changes how much energy the planet absorbs, with potentially dramatic consequences. “I like it because it deals with simple concepts, but it’s important,” Perovich told me.

At one point, Perovich asked me to imagine that we were looking down at the earth from a spaceship hovering above the North Pole. “It’s springtime, and the ice is covered with snow, and it’s really bright and white,” he said. “It reflects over 80 percent of the incident sunlight. The albedo’s around 0.8, 0.9. Now, let’s suppose that we melt that ice away and we’re left with the ocean. The albedo of the ocean is less than 0.1; it’s like 0.07.

“Not only is the albedo of the snow-covered ice high; it’s the highest of anything we find on earth,” he went on. “And not only is the albedo of water low; it’s pretty much as low as anything you can find on earth. So what you’re doing is you’re replacing the best reflector with the worst reflector.” The more open water that’s exposed, the more solar energy goes into heating the ocean. The result is a positive feedback, similar to the one between thawing permafrost and carbon releases, only more direct. This so-called ice-albedo feedback is believed to be a major reason that the Arctic is warming so rapidly.

“As we melt that ice back, we can put more heat into the system, which means we can melt the ice back even more, which means we can put more heat into it, and, you see, it just kind of builds on itself,” Perovich said. “It takes a small nudge to the climate system and amplifies it into a big change.”

A few dozen miles to the east of CRREL, not far from the Maine–New Hampshire border, is a small park called the Madison Boulder Natural Area. The park’s major—indeed, only—attraction is a block of granite the size of a two-story house. The Madison Boulder is thirty-seven feet wide and eighty-three feet long and weighs about ten million pounds. It was plucked out of the White Mountains and deposited in its current location eleven thousand years ago, and it illustrates how relatively minor changes to the climate system can, when amplified, yield monumental results.

Geologically speaking, we are now living in a warm period after an ice age. Over the past two million years, huge ice sheets have advanced across the Northern Hemisphere and retreated again more than twenty times. (Each major advance tended, for obvious reasons, to destroy the evidence of its predecessors.) The most recent advance, called the Wisconsin, began roughly 120,000 years ago. Ice began to creep outward from centers in Scandinavia, Siberia, and the highlands near Hudson Bay, spreading gradually across what is now Europe and Canada. By the time the sheets had reached their maximum southern extent, most of New England and New York and a good part of the upper Midwest were buried under ice nearly a mile thick. The ice sheets were so heavy that they depressed the crust of the earth, pushing it down into the mantle. (In some places, the process of recovery, called isostatic rebound, is still going on.) As the ice retreated, at the start of the current interglacial—the Holocene—it deposited, among other landmarks, the terminal moraine known as Long Island.

It is now known, or at least almost universally accepted, that glacial cycles are initiated by slight, periodic variations in the earth’s orbit. These orbital variations, which are caused by, among other things, the gravitational pull of the other planets, alter the distribution of sunlight at different latitudes during different seasons and occur according to a complex cycle that takes a hundred thousand years to complete. Orbital variations in themselves, however, aren’t sufficient to produce the sort of massive ice sheet that picked up the Madison Boulder.

The crushing size of that ice sheet, the Laurentide, which stretched over some five million square miles, was the result of feedbacks, more or less analogous to those now being studied in the Arctic, only operating in reverse. As the ice spread, albedo increased, leading to less heat absorption and the growth of yet more ice. At the same time, for reasons that are not entirely understood, as the ice sheets advanced, CO
₂
levels declined: during each of the most recent glaciations, carbon dioxide levels dropped almost precisely in sync with falling temperatures. During each warm period, when the ice retreated, CO
₂
levels rose again. Researchers who have studied this history have concluded that fully half the temperature difference between cold periods and warm ones can be attributed to changes in the concentrations of greenhouse gases.

While I was at CRREL, Perovich took me to meet a colleague of his named John Weatherly. Posted on Weatherly’s office door was a bumper sticker designed to be pasted—illicitly—on SUVs. It said, i’m changing the climate! ask me how! Weatherly is a climate modeler, and for the past several years, he and Perovich have been working to translate the data gathered on the
Des Groseilliers
expedition into computer algorithms to be used in climate forecasting. Weatherly told me that some climate models—worldwide, there are about fifteen major ones in operation—predict that the perennial sea-ice cover in the Arctic will disappear entirely by the year 2080. At that point, although there would continue to be seasonal ice that forms in winter, in summer the Arctic Ocean would be completely ice-free. “That’s not in our lifetime,” he observed. “But it is in the lifetime of our kids.”

Later, back in his office, Perovich and I talked about the long-term prospects for the Arctic. Perovich noted that the earth’s climate system is so vast that it is not easily altered. “On the one hand, you think, It’s the earth’s climate system; it’s big, it’s robust. And, indeed, it has to be somewhat robust or else it would be changing all the time.” On the other hand, the climate record shows that it would be a mistake to assume that change, when it comes, will come gradually. Perovich offered a comparison that he had heard from a glaciologist friend. The friend likened the climate system to a rowboat: “You can tip and then you’ll just go back. You can tip it and just go back. And then you tip it and you get to the other stable state, which is upside down.”

Perovich said that he also liked a regional analogy. “The way I’ve been thinking about it, riding my bike around here, is, You ride by all these pastures and they’ve got these big granite boulders in the middle of them. You’ve got a big boulder sitting thereon this rolling hill. You can’t just go by this boulder. You’ve got to try to push it. So you start rocking it, and you get a bunch of friends, and they start rocking it, and finally it starts moving. And then you realize, Maybe this wasn’t the best idea. That’s what we’re doing as a society. This climate, if it starts rolling, we don’t really know where it will stop.”

Chapter 2

A Warmer Sky

As a cause for alarm, global warming could be said to be a 1970s idea; as pure science, however, it is much older than that. In the late 1850s, an Irish physicist named John Tyndall set out to study the absorptive properties of various gases. What he discovered led him to propose the first accurate account of how the atmosphere functions.

Tyndall, who was born in County Carlow in 1820, left school at the age of seventeen or eighteen and went to work as a surveyor for the British government. Pursuing his education at night, he subsequently became a mathematics teacher, and then, although he spoke no German, set off for Marburg to study with Robert Wilhelm Bunsen (for whom the Bunsen burner would later be named). After Tyndall received his Ph.D.—the degree was at the time just being established—he had trouble supporting himself until, in 1853, he was invited to deliver a single lecture at London’s Royal Institution, then one of Britain’s leading scientific centers. Based on the talk’s success, Tyndall was invited to deliver another, and then another, and a few months later was elected to a professorship in natural philosophy. His lectures were enormously popular—many were collected and published—a fact that testifies both to Tyndall’s considerable skills as a speaker and also to the intellectual interests of the Victorian middle class. Eventually, Tyndall went on a lucrative speaking tour of the United States, the proceeds from which he placed in a special trust to be used for the advancement of American science.

Tyndall’s research varied almost impossibly widely, from optics to acoustics to glacial motion. (He was an avid mountain climber, and made frequent trips to the Alps to study the ice.) One of his most enduring interests was in the science of heat, which, in the mid-nineteenth century, was rapidly evolving. In 1859, Tyndall built the world’s first ratio spectrophotometer, a device that allowed him to compare the way different gases absorb and transmit radiation. When Tyndall tested the most common gases in the air—nitrogen and oxygen—he found they were transparent to both visible and infrared radiation. (The latter of these he called “ultra-red” radiation.) Other gases, like carbon dioxide, methane, and water vapor, however, were not. CO
₂
and water vapor were transparent in the visible part of the spectrum, but partly opaque in the infrared. Tyndall was quick to appreciate the implications of his discovery: the selectively transparent gases, he declared, were largely responsible for determining the planet’s climate. He likened their impact to that of a dam built across a river: just as a dam “causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial rays, produces a local heightening of the temperature at the earth’s surface.”