by Carl Sagan
Also, changes in the weather affect animals and microbes that carry disease. Recent outbreaks of cholera, malaria, yellow fever, dengue fever, and the hantavirus pulmonary syndrome are all suspected of being related to changing weather. One recent medical estimate is that the increase in the area of the Earth occupied by the tropics and subtropics, and the resulting burgeoning population of malaria-bearing mosquitos, would by the end of the next century result in 50 to 80 million additional cases of malaria each year. Unless something is done. A 1996 U.N. scientific report argues, “If adverse population health impacts are likely to result from climate change, we do not have the usual option of seeking definitive empirical evidence before acting. A wait-and-see approach would be imprudent at best and nonsensical at worst.”
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 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, Rhône, 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 skepticism 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 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 the 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 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?
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The vigor and importance of environmental i
ssues 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 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.
* Again, because CFCs both deplete the ozone layer and contribute to global warming, there has been some confusion between these two very different environmental results.
CHAPTER 12
ESCAPE FROM
AMBUSH
[P]lainly, nobody will be afraid who believes nothing can happen to him.… [F]ear is felt by those who believe something is likely to happen to them.… People do not believe this when they are, or think they are, in the midst of great prosperity, and are in consequence insolent, contemptuous and reckless.… [But if] they are to feel the anguish of uncertainty, there must be some faint expectation of escape.
ARISTOTLE (384–322 B.C.),
Rhetoric, 1382b29
What must we do? Because the carbon dioxide that we put up into the atmosphere today will stay there for decades, even major efforts at technological self-control will do no good until a generation into the future—although the contributions by some other gases to global warming can be reduced more quickly. We need to distinguish between short-term mitigation and long-term solutions, although both are needed. We must, it seems, phase in as quickly as possible a new world energy economy that doesn’t generate nearly so much greenhouse gases and other pollutants. But “as quickly as possible” will take decades at least to complete, and we must in the meantime lessen the damage, taking great care that the transition does as little damage as possible to the world’s social and economic fabric, and that standards of living do not decline in consequence. The only question is whether we manage the crisis or it manages us.
Almost two out of three Americans call themselves environmentalists—according to a 1995 Gallup poll—and would give protecting the environment priority over economic growth. Most would acquiesce to increased taxes if earmarked for environmental protection. Still, it might turn out that all this is impossible—that the vested industrial interests are so powerful and consumer resistance so weak that no significant change from business-as-usual will occur until it’s too late, or that the transition to a non-fossil-fuel civilization will so stress an already fragile world economy as to cause economic chaos. Plainly, we must pick our way warily. There’s a natural tendency to temporize: This is unknown territory. Shouldn’t we go slowly? But then we take a look at the maps of projected climate change and we recognize that we cannot temporize, that it’s foolhardy to go too slowly.
The biggest CO2 emitter on the planet is the United States. The next biggest CO2 emitter is Russia and the other republics of the former Soviet Union. The third biggest, if we combine them, is all the developing countries together. That’s a very important fact: This isn’t just a problem for the highly technological nations—through slash-and-burn agriculture, burning firewood, and so on, developing countries are also making a major contribution to global warming. And the developing countries have the world’s largest population growth rate. Even if they don’t succeed in achieving something like the standard of living of Japan, the Pacific Crescent, and the West, these nations will constitute a steadily increasing part of the problem. Next in order of complicity is Western Europe, then China, and only then Japan, one of the most fuel-efficient nations on Earth. Again, just as the cause of global warming is worldwide, any solution must also be worldwide.
The scale of change necessary to address this problem at its core is nearly daunting—especially for those policymakers who are mainly interested to do things that will benefit them during their terms of office. If the required action to make things better could be subsumed in 2-, 4-, or 6-year programs, politicians would be more supportive, because then the political benefits might accrue when it’s time for reelection. But 20-, 40-, or 60-year programs, where the benefits accrue not only when the politicians are out of office, but when they’re dead, are politically less attractive.
Certainly we must be careful not to rush off half-cocked like Croesus and discover that at huge expense we’ve done something unnecessary or stupid or dangerous. But even more irresponsible is to ignore an impending catastrophe and naïvely hope it will go away. Can’t we find some middle ground of policy response, which is appropriate to the seriousness of the problem, but which does not ruin us in case somehow—a negative feedback deus ex machina, for example—we have overestimated the severity of the matter?
Say you’re designing a bridge or skyscraper. It’s customary to build in, to demand, a tolerance to catastrophic failure far beyond what the likely stresses will be. Why? Because the consequences of the collapse of the bridge or skyscraper are so serious, you must be sure. You need very reliable guarantees. The same approach, I think, must be adopted for local, regional, and global environmental problems. And here, as I’ve said, there is great resistance, in part because large amounts of money are required from government and industry. For this reason, we will increasingly see attempts to discredit global warming. But money is also needed to truss up bridges and to reinforce skyscrapers. This is considered a normal part of the cost of building big. Designers and builders who cut corners and take no such precautions are not considered prudent capitalists becaus
e they don’t waste money on implausible contingencies. They are considered criminals. There are laws to make sure bridges and skyscrapers don’t fall down. Shouldn’t we also have laws and moral proscriptions treating the potentially far more serious environmental issues?
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I want now to offer some practical suggestions about dealing with climate change. I believe they represent the consensus of a large number of experts, although doubtless not all. They constitute only a beginning, only an attempt to mitigate the problem, but at an appropriate level of seriousness. To undo global warming and bring the Earth’s climate back to what it was, say, in the 1960s will be much more difficult. The proposals are modest in another respect as well—they all have excellent reasons for being carried out, independent of the global warming issue.
With systematic monitoring of the Sun, atmosphere, clouds, land, and ocean from space, aircraft, ships, and from the ground, using a wide range of sensing systems, we should be able to diminish the range of current uncertainty, identify feedback loops, observe regional pollution patterns and their effects, track the withering of the forests and the growth of deserts, monitor changes in the polar ice caps, in glaciers, and in the level of the oceans, examine the chemistry of the ozone layer, observe the spread of volcanic debris and its climatic consequences, and scrutinize changes in how much sunlight arrives at Earth. We have never before had such powerful tools to study and to safeguard the global environment. While spacecraft of many nations are about to play a role, the premier such tool is NASA’s robotic Earth Observing System, part of its Mission to Planet Earth.