Field Notes From a Catastrophe: Man, Nature, and Climate Change (12 page)

One day, when I was talking to Hansen in his cluttered office, he pulled a pair of photographs out of his briefcase. The first showed a chubby-faced five-year-old girl holding some miniature Christmas-tree lights in front of an even chubbier-faced five-month-old baby. The girl, Hansen told me, was his granddaughter Sophie and the boy was his new grandson, Connor. The caption on the first picture read, “Sophie explains greenhouse warming.” The caption on the second photograph, which showed the baby smiling gleefully, read, “Connor gets it.”

When modelers talk about what drives the climate, they focus on what they call “forcings.” A forcing is any ongoing processor discrete event that alters the energy of the system. Examples of natural forcings include, in addition to volcanic eruptions, periodic shifts in the earth’s orbit and changes in the sun’s output, like those linked to sunspots. Many climate shifts of the past have no known forcing associated with them; for instance, no one is certain what brought about the so-called Little Ice Age, the cool period that lasted in Europe from around 1500 to 1850. A very large forcing, meanwhile, should produce a commensurately large—and obvious—effect. One GISS scientist put it to me this way: “If the sun went supernova, there’s no question that we could model what would happen.”

Adding carbon dioxide, or any other greenhouse gas, to the atmosphere by, say, burning fossil fuels or leveling forests is, in the language of climate science, an anthropogenic forcing. Since preindustrial times, the concentration of CO
₂
in the atmosphere has risen by roughly a third, from 280 to 378 parts per million. During the same period, the concentration of methane has more than doubled, from .78 to 1.76 parts per million. Scientists measure forcings in terms of watts per square meter, or w/m
²
, by which they mean that a certain number of watts have been added (or, in the case of a negative forcing, like aerosols, subtracted) for every single square meter of the earth’s surface. The size of the greenhouse forcing is estimated, at this point, to be 2.5 w/m
²
. A miniature Christmas light gives off about four tenths of a watt of energy, mostly in the form of heat, so that, in effect (as Sophie supposedly explained to Connor), we have covered the earth with tiny bulbs, six for every square meter. These bulbs are burning twenty-four hours a day, seven days a week, year in and year out.

If greenhouse gases were held constant at today’s levels, it is estimated that it would take several decades for the full impact of the forcing that is already in place to be felt. This is because raising the earth’s temperature involves not only warming the air and the surface of the land but also melting sea ice, liquefying glaciers, and, most significant, heating the oceans, all processes that require tremendous amounts of energy. (Imagine trying to thaw a gallon of ice cream or warm a pot of water using an Easy-Bake oven.) The delay that is built into the system is, in a certain sense, fortunate. It enables us, with the help of climate models, to foresee what is coming and therefore to prepare for it. But in another sense it is clearly disastrous, because it allows us to keep adding CO
₂
to the atmosphere while fobbing the impacts off on our children and grandchildren.

There are two ways to operate a climate model. In the first, which is known as a transient run, greenhouse gases are slowly added to the simulated atmosphere—just as they would be to the real atmosphere—and the model forecasts what the effect of these additions will be at any given moment. In the second, greenhouse gases are added to the atmosphere all at once, and the model is run at these new levels until the climate has fully adjusted to the forcing by reaching a new equilibrium. (Not surprisingly, this is known as an equilibrium run.)

For doubled CO
₂
, equilibrium runs of the GISS model predict that average global temperatures will rise by 4.9 degrees Fahrenheit. Only about third of this increase is directly attributable to higher greenhouse gas levels. The rest is a result of indirect effects, like the melting of sea ice, which allows the earth to absorb more heat. The most significant indirect effect is known as the “water-vapor feedback.” Since warmer air holds more moisture, higher temperatures are expected to produce an atmosphere containing more water vapor, which is itself a greenhouse gas. GISS’s forecast is on the low end of the most recent projections for doubled CO
₂
; the Hadley Centre model, which is run by the British Met Office, predicts that under these conditions, the eventual temperature rise will be 6.3 degrees Fahrenheit, while Japan’s National Institute for Environmental Studies predicts that it will be 7.7 degrees.

In the context of ordinary life, a warming of 4.9, or even of 7.7, degrees may not seem like much to worry about. On the dreary November day I attended the GISS modeling meeting, the temperature in Central Park was fifty-two degrees at seven A.M., and by two P.M. had reached sixty degrees. In the course of a normal summer’s day, air temperatures routinely rise by fifteen degrees or more. Average global temperatures, however, have practically nothing to do with ordinary life. This is perhaps best illustrated by the ups and downs of climate history. The so-called Last Glacial Maximum—the point during the most recent glaciation when the ice sheets reached their maximum extent —occurred about twenty thousand years ago. At that time, the Laurentide ice sheet reached deep into what is now the northeastern and midwestern United States, and sea levels were so low that Siberia and Alaska were connected by a land bridge nearly a thousand miles wide. During the Last Glacial Maximum, average global temperatures were only about ten degrees colder than they are today. It is worth noting that the total forcing that ended that ice age is estimated to have been just six and a half watts per square meter.

David Rind is a climate scientist who has worked at GISS since 1978. Rind acts as a troubleshooter for the institute’s model, scanning reams of numbers known as diagnostics, trying to catch problems, and he also works with what is known as the GISS Climate Impacts Group. (His office, like Hansen’s, is filled with dusty piles of computer printouts.) Although higher temperatures are the most predictable result of increased CO
₂
, other, second-order consequences—rising sea levels, changes in vegetation, loss of snow cover—are likely to be just as significant. Rind’s particular interest is how CO
₂
levels will affect water supplies, because, as he put it to me, “you can’t have a plastic version of water.”

One afternoon, when I was talking to Rind in his office, he mentioned a visit that President George W. Bush’s science adviser, John Marburger III, had paid to GISS a few years earlier. “He said,‘We’re really interested in adaptation to climate change,’ ” Rind recalled. “Well, what does ‘adaptation’ mean?” He rummaged through one of his many file cabinets and finally pulled out a paper that he had published in the
Journal of Geophysical Research
titled “Potential Evapotranspiration and the Likelihood of Future Drought.” In much the same way that wind velocity is measured using the Beaufort scale, water availability is measured using the Palmer Drought Severity Index. Different climate models offer very different predictions about future water availability; in the paper, Rind applied the criteria used in the Palmer index to GISS’s model and also to a model operated by the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory. He found that as carbon dioxide levels rose, the world would begin to experience more and more serious water shortages, starting near the equator and then spreading toward the poles. When he applied the index to the GISS model for doubled CO
₂
, it showed most of the continental United States would be suffering under severe drought conditions. When he applied the index to the GFDL model, the results were even more dire. Rind created two maps to illustrate these findings. Yellow represented a 40 to 60 percent chance of summertime drought, ochre a 60 to 80 percent chance, and brown an 80 to 100 percent chance. In the first map, showing the GISS results, the Northeast was yellow, the Midwest was ochre, and the Rocky Mountain states and California were brown. In the second, showing the GFDL results, brown covered practically the entire country.

“I gave a talk based on these drought indices out in California to water-resource managers,” Rind told me. “And they said, ‘Well, if that happens, forget it.’ There’s just no way they could deal with that.”

He went on, “Obviously, if you get drought indices like these, there’s no adaptation that’s possible. But let’s say it’s not that severe. What adaptation are we talking about? Adaptation in 2020? Adaptation in 2040? Adaptation in 2060? Because the way the models project this, as global warming gets going, once you’ve adapted to one decade, you’re going to have to change everything the next decade.

“We may say that we’re more technologically able than earlier societies. But one thing about climate change is it’s potentially geopolitically destabilizing. And we’re not only more technologically able; we’re more technologically able destructively as well. I think it’s impossible to predict what will happen. I guess—though I won’t be around to see it—I wouldn’t be shocked to find out that by 2100 most things were destroyed.” He paused. “That’s sort of an extreme view.”

On the other side of the Hudson River and slightly to the north of GISS, the Lamont-Doherty Earth Observatory occupies what was once a weekend estate in the town of Palisades, New York. The observatory is an outpost of Columbia University, and it houses, among its collections of natural artifacts, the world’s largest assembly of ocean-sediment cores—more than thirteen thousand in all. The cores are kept in steel compartments that look like drawers from a filing cabinet, only longer and much skinnier. Some of the cores are chalky, some are clayey, and some are made up almost entirely of gravel. All can be coaxed to yield up—in one way or another—information about past climates.

Peter deMenocal is a paleoclimatologist who has worked at Lamont-Doherty for fifteen years. DeMenocalis an expert on ocean cores, and also on the climate of the Pliocene, which lasted from roughly five million to two million years ago. Around two and a half million years ago, the earth, which had been warm and relatively ice-free, started to cool down until it entered an era—the Pleistocene—of recurring glaciations. DeMenocal has argued that this transition was a key event in human evolution: right around the time that it occurred, at least two types of hominids—one of which would eventually give rise to modern man—branched off from a single ancestral line. Until quite recently, paleoclimatologists like deMenocal rarely bothered with anything much closer to the present day; the current interglacial—the Holocene—was believed to be too stable to warrant much study. In the mid-nineties, though, deMenocal, motivated by a growing concern over global warming—and a concomitant shift in government research funds—decided to look in detail at some Holocene cores. What he learned about the period, as he put it to me when I visited him at Lamont-Doherty, was that it was “less boring than we had thought.”

One way to extract climate data from ocean sediments is to examine the remains of what lived or, perhaps more pertinently, what died and was buried there. The oceans are rich with microscopic creatures known as foraminifera—forams, for short. Forams are tiny, single-celled organisms that construct shells out of calcite. These shells come in a wide range of shapes; viewed under a microscope, some look like tiny sand dollars, others like conch shells, and still others like lumps of dough. There are about thirty planktonic species of foraminifera—which is to say, species that live near the top of the sea—and each thrives at a different water temperature, so that by counting a species’ prevalence in a given sample it is possible to estimate how warm (or cold) the ocean was at the time the sediment was formed. When deMenocal used this technique to analyze cores that had been collected off the coast of Mauritania, he found that they contained evidence of recurring cool periods; every fifteen hundred years or so, water temperatures would drop for a few centuries before climbing back up again. (The most recent cool period corresponds to the Little Ice Age, which ended about a century and a half ago.) The cores also showed dramatic changes in precipitation. Until about six thousand years ago, northern Africa was relatively wet—dotted with small lakes. Then it became dry, as it is today. DeMenocal traced the shift to periodic variations in the earth’s orbit, which, in a generic sense, are the same forces that trigger ice ages. But orbital changes occur gradually, over thousands of years, and northern Africa appears to have switched from wet to dry all of a sudden. Although no one knows exactly how this happened, it seems, like so many climate events, to have been a function of feedbacks—the less rain the continent got, the less vegetation there was to retain water, and so on until, finally, the system just flipped. The process provides yet more evidence of how a very small forcing sustained over time can produce dramatic results.

“We were kind of surprised by what we found,” deMenocal told me about his work on the supposedly stable Holocene. “Actually, more than surprised. It was one of these things where, you know, in life you take certain things for granted, like your neighbor’s not going to be an ax murderer. And then you discover your neighbor
is
an ax murderer.”

Not long after deMenocal began to think about the Holocene, a brief mention of his work on the climate of Africa appeared in a book produced by
National Geographic
. On the facing page, there was a piece on Harvey Weiss and his work at Tell Leilan. DeMenocal vividly remembers his reaction. “I thought, Holy cow, that’s just amazing!” he told me. “It was one of these cases where I lost sleep that night, I just thought it was such a cool idea.”