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The climate predicted for the next century depends on whether we put greenhouse gases into the atmosphere at the present rate, or at an accelerated rate, or at a diminished rate. The more greenhouse gases, the hotter it gets. Even assuming only moderate increases, temperatures apparently will rise significantly. But these are global averages; some places will be much colder and some much warmer. Large areas of increasing drought are predicted. In many models great food-producing areas of the world, in South and Southeast Asia, Latin America, and sub-Saharan Africa, are predicted to become hot and parched.

Some agricultural exporting nations in middle to high latitudes (the United States, Canada, Australia, for example) may actually gain at first and their exports soar. Poor nations will be most severely impacted. In the twenty-first century, in this as in many other ways, the global disparity between rich and poor may increase dramatically. Millions of people, their children starving, with very little to lose, pose a practical and serious problem for the rich—as the history of revolution teaches.

The chance of a drought-driven global agricultural crisis begins to become significant around 2050. Some scientists think that the chance of a massive worldwide agricultural failure from greenhouse warming by the year 2050 is low—perhaps only 10 percent. But of course the longer we wait, the greater the chances are. For a while some places—Canada, Siberia—might get better (if the soil is suitable for agriculture), even if the lower latitudes get worse. Wait long enough and the climate deteriorates worldwide. As the Earth warms, sea level rises. By the end of the next century, sea level may have risen by tens of centimeters, and, just possibly, by a meter. This is partly due to the fact that seawater expands as it warms, and partly due to the melting of glacial and Ambush: The Warming of the World • 135

polar ice. As time continues, sea level rises still more. No one knows when it will happen, but eventually many populated islands in Polynesia, Melanesia, and the Indian Ocean will, according to the projections, be wholly submerged, and disappear from the face of the Earth. Understandably enough, an Alliance of Small Island States has constituted itself, militantly opposed to further increases in greenhouse gases. Devastating impacts are also predicted for Venice, Bangkok, Alexandria, New Orleans, Miami, New York City, and more generally for the highly populated areas of the Mississippi, Yangtze, Yellow, Rhine, Rhone, Po, Nile, Indus, Ganges, Niger, and Mekong rivers. Rising sea level will displace tens of millions of people in Bangladesh alone. There will be a vast new problem of environmental refugees—as populations grow, environments deteriorate, and social systems become increasingly incompetent to deal with rapid change. Where are they supposed to go? Similar problems can be anticipated for China. If we keep on with business as usual, the Earth will be warmed more every year; drought and floods both will be endemic; many more cities, provinces, and whole nations will be submerged beneath the waves— unless heroic worldwide engineering countermeasures are taken. In the longer run, still more dire consequences may follow, including the collapse of the West Antarctic ice sheet, its surge into the sea, a major global rise in sea level, and the inundation of almost all coastal cities on the planet. Models of global warming show different effects—on temperature, drought, weather, and rising sea level, for example— becoming noticeable on different timescales, from decades to a century or two. These consequences seem so unpleasant and so expensive to fix that naturally there has been a serious effort to find something wrong with the story. Some of the efforts are motivated by nothing more than the standard scientific skepti-136 • Billions and Billions cism about all new ideas; others are motivated by the profit motive in the affected industries. One key issue is feedback.

There are both positive and negative feedbacks possible in the global climate system. Positive feedbacks are the dangerous kind. Here's an example of a positive feedback: The temperature increases a little bit because of the greenhouse effect and so some polar ice melts. But polar ice is bright compared to the open sea. As a result of that melting, then, the Earth is now very slightly darker; and because the Earth is darker, it now absorbs slightly more sunlight, so it heats some more, so it melts some more polar ice, and the process continues—perhaps to run away. That's a positive feedback. Another positive feedback: A little more CO2 in the air heats the surface of the Earth, including the oceans, a little bit. The now warmer oceans vaporize a little more water vapor into the atmosphere. Water vapor is also a greenhouse gas, so it holds in more heat and the temperature gets higher.

Then there are negative feedbacks. They're homeostatic. An example: Heat up the Earth a little bit by putting more carbon dioxide, say, into the atmosphere. As before, this injects more water vapor into the atmosphere, but this generates more clouds. Clouds are bright; they reflect more sunlight into space, and therefore less sunlight is available to heat the Earth. The increase in temperature eventually works a decrease in temperature. Or, another possibility: Put a little more carbon dioxide into the atmosphere. Plants generally like more carbon dioxide, so they grow faster, and in growing faster, they take more carbon dioxide from the air—which in turn reduces the greenhouse effect. Negative feedbacks are like thermostats in the global climate. If, by luck, they were to be very powerful, maybe greenhouse warming would be self-limiting, and we could have

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the luxury of emulating Cassandra's listeners without sharing their fate.

The question is: Balance all the positive and all the negative feedbacks and where do you wind up? The answer is: Nobody is absolutely sure. Retrospective attempts to calculate global warming and cooling during the ice ages as fhe amount of greenhouse gases increased and decreased give the right answer. Put another way, calibrating the computer models by forcing agreement with the historical data will automatically account for all feedback mechanisms, known and unknown, in the natural climate machine. But it might be that as the Earth is pushed into climatic regimes unknown in the last 200,000 years, new feedbacks might occur of which we are ignorant. For example, much methane is sequestered in bogs (which sometimes produces the eerily beautiful dancing lights called "will-o-the-wisps"). It might begin to bubble up at an increasing pace as the Earth warms. The additional methane warms the Earth still further, and so on, another positive feedback.

Wallace Broecker of Columbia University points to the very quick warming that happened about 10,000 B.C., just before the invention of agriculture. It's so steep that, he believes, it implies an instability in the coupled ocean-atmosphere system; and that if you push the Earth's climate too hard in one direction or another, you cross a threshold, there's a kind of "bang," and the whole system runs away by itself to another stable state. He proposes that we may be teetering on just such an instability right now. This consideration only makes things worse, maybe much worse.

In any case, it's pretty clear that the faster the climate is changing, the more difficult it is for whatever homeostatic systems there are to catch up and stabilize. I wonder if we're not

138 • Billions and Billions more likely to miss unpleasant feedbacks than comforting ones. We're not smart enough to predict everything. That's certainly clear. I think it's unlikely that the sum of what we're too ignorant to figure out will save us. Maybe it will. But would we want to bet our lives on it?

The vigor and importance of environmental issues is reflected in the meetings of professional scientific societies. For example, the American Geophysical Union is the largest organization of Earth scientists in the world. At a recent (1993) annual meeting, there was a session on previous warm episodes in Earth history, with an eye toward understanding what the consequences for global warming might be. The very first paper warns that "because future warming trends will be very rapid, there are no exact analogues for a 21st century greenhouse warming." There were four half-day sessions devoted to ozone depletion, and three sessions on the cloud/climate feedback. An additional three sessions were devoted to more general studies of the climates of the past. J. D. Mahlman of NOAA began his lecture by noting, "The discovery of the remarkably large Antarctic ozone losses in the 1980s was an event totally unpredicted by anyone." A paper from the Byrd Polar Research Center at Ohio State University offers evidence from ice cores in the West China and Peruvian glaciers for recent warming of the Earth compared to the temperatures over the last 500 years.

Considering how contentious the scientific community is, it is notable that not a single paper is offered claiming that depletion of the ozone layer or global warming are snares and delusions, or that there always was a hole in the ozone layer over Antarctica, or that global warming will be considerably less than the estimated 1° to 4°C for a doubling in the carbon dioxide

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abundance. The rewards for finding that there is no ozone depletion or that global warming is insignificant are very high. There are many powerful and wealthy industries and individuals that would benefit if only such contentions were true. But as the programs of scientific meetings indicate, this is probably a forlorn hope. **

Our technical civilization now poses a real danger to itself. All over the world fossil fuels are simultaneously degrading respiratory health, the life of forests, lakes, coastlines, and oceans, and the world climate. Nobody intended to do any harm, surely. The captains of the fossil fuel industry were simply trying to make a profit for themselves and their shareholders, to provide a product everyone wanted, and to support the military and economic power of whatever nations they happened to be situated in. The facts that this was inadvertent, that intentions were benign, that most of us in the developed world have benefitted from our fossil fuel civilization, that many nations and many generations all contributed to the problem all suggest that this is no time for finger-pointing. No one nation or generation or industry got us into this mess, and no one nation or generation or industry can by itself get us out. If we are to prevent this climatic danger from working its worst, we will simply all have to work together, and for a long time. The principal obstacle is, of course, inertia, resistance to change—huge, worldwide, interlocking industrial, economic, and political establishments all beholden to fossil fuels, when fossil fuels are the problem. In the United States, as the evidence for the seriousness of global warming mounts, the political will to do something about it seems to be shriveling. CHAPTER 12

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