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Human society is now at risk of destroying itself by stumbling into either a nuclear holocaust or an environmental holocaust. The latter could arise from mass extinction of species. This chapter estimates how many species we have already exterminated, how many more we are likely to exterminate within the next century, and how mass extinction would affect us. Until our own generation, no one had grounds to worry whether the next human generation would survive or enjoy a planet worth living on. Ours is the first generation to be confronted with these questions about its children's future. We devote much of our lives to training our children to support themselves and to get along with other people. Increasingly, we are asking ourselves whether all those efforts of ours might be wasted.

These concerns arise because of two clouds hanging over usclouds that would have similar consequences, but that we view very differently. One, the risk of a nuclear holocaust, first revealed itself in the cloud over Hiroshima. Everyone agrees that the risk is real, since there are huge stockpiles of nuclear weapons and since politicians throughout history have occasionally made dumb miscalculations. Everyone agrees that, if a nuclear holocaust does happen, it will be bad for us and might even kill us all. This risk shapes much of current world diplomacy. The only thing about which we disagree is how best to handle itfor instance, whether we should aim for complete or partial nuclear disarmament, nuclear balance, or nuclear superiority.

The other cloud is the risk of an environmental holocaust, of which one often discussed potential cause is the gradual extinction of most of the World's species. In contrast to the case with nuclear holocaust, there is almost complete disagreement about whether the risk of a mass extinction is real and about whether it would really do us much harm if it happened. For instance, one of the most frequently cited estimates is that humans have caused about one per cent of the world's bird species to be, come extinct within the last few centuries. At one extreme, many thoughtful peopleespecially economists and industrial leaders, but also some biologists and many laypeoplethink that that loss of one per cent would have been inconsequential, even if it had really happened. In fact, such people reason that one per cent is a gross overestimate, that most species are superfluous to us, and that it would do us no harm to lose ten times more species. At the opposite extreme, many other thoughtful peopleespecially conservation biologists and a growing number of laypeople belonging to environmentalist movementsthink that the one per cent figure is a gross underestimate, and that mass extinction would undermine the quality or possibility of human life. Obviously, it will make a big difference to our children which of these two extreme views is closer to the truth.

The risks of a nuclear holocaust and of an environmental holocaust constitute the two really pressing questions facing the human race today. Compared to these two clouds, our usual obsessions with cancer, AIDS, and diet pale into insignificance, because those problems do not threaten the survival of the human species. If the nuclear and environmental risks should not materialize, we shall have plenty of leisure time to solve bagatelles like cancer. If we fail to avert those two risks, solving cancer will not have helped us anyway.

How many species have humans really driven into extinction already? How many more are likely to become extinct within our children's lifetimes? If more do become extinct, so what? How much do wrens contribute to our gross national product? Are not all species destined to become extinct sooner dr later? Is the claimed mass extinction crisis an hysterical fantasy, a real risk for the future, or a proven event that is already well underway?

We need to go through three steps if we are to arrive at realistic estimates of the numbers involved in the mass extinction debate. Firstly, let's see how many species have become extinct in modern times (that is, since 1600). Secondly, let's estimate how many other species had become extinct before 1600. As the third step, let's try to predict how many further sp*ecies are likely to become extinct within the lifespans of ourselves, our children, and our grandchildren. Finally, let's ask what difference it all makes to us anyway.

The first step, that of calculating the number of species that have become extinct in modern times, seems easy when one initially thinks about it. Just take some group of plants or animals, count up in a catalogue the total number of species, mark off the ones known to have become extinct since 1600, and add them up. As a group on which to try this exercise, birds have the advantage that they are easy to see and identify, and hoards of bird-watchers watch them. As a result, more is known about them than about any other group of animals.

Approximately 9,000 species of birds exist today. Only one or two previously unknown species are still being discovered each year, so virtually all living birds have already been named. The leading agency concerned with the status of the world's birdsthe International Council for Bird Preservation (ICBP)lists 108 species of birds, plus many additional subspecies, as having become extinct since 1600. Virtually all these cases of extinction were caused in one way or another by humansmore of that later. One hundred and eight is about one per cent of that total number of bird species: 9,000. That is where the one per cent figure I mentioned earlier comes from.

Before we take that as the final word on the number of modern birds that have become extinct, let's understand how the number of 108 was arrived at. The ICBP decides to list a species as extinct only after that bird has been specifically looked for in areas where it was previously known to occur or might have turned up, and after it has not been found for many years. In many cases, birders have watched a population dwindle down to a few individuals and have followed the fates of those last individuals. For example, the most recent subspecies of bird to have become extinct in the US was the dusky seaside sparrow that lived in marshes near Titusville, Florida. As its population shrank due to destruction of the marshes where it lived, wildlife agencies put identification bands on the few remaining sparrows so that they could be individually recognized. When only six remained, they were brought into captivity in order to protect and breed them. Unfortunately, one after another died. The last individual, and with it the subspecies itself, died on 16 June 1987.

Thus, there is no doubt that the dusky seaside sparrow is extinct. Equally little doubt attaches to the many other subspecies and the 108 full species of birds listed as extinct. The full species listed as having vanished m North America since European settlement, and the years in which the last individual of each died, are the great auk (1844), spectacled cormorant (1852), Labrador duck (1875), Carolina parakeet (1914), and passenger pigeon (1914). The great auk also formerly occurred in Europe, but no other European bird species is listed as having become extinct since 1600, though some species have disappeared within Europe while surviving on other continents. What about all those remaining bird species that did not fulfil the BP's rigorous criteria for extinction? Can we be certain that they still exist? For most North American and European birds the answer is 'yes'. Hundreds of thousands of fanatical birdwatchers monitor all bird species on these continents every year. The rarer the species, the more fanatical is the annual search for it. No North American or European bird species could possibly drift into extinction unnoticed. There is only one North American bird species whose current existence is uncertain, the Bachman's warbler, last definitely recorded in 1977, but the ICBP hasn't given up hope for it because of more recent unconfirmed records. (The ivory-billed woodpecker may also be extinct, but the North American population is 'only' a subspecies; a few individuals of the other subspecies of this woodpecker survive in Cuba.) Thus, the number of North American bird species that have suffered extinction since 1600 is surely not less than five nor more than six. Every species but Bachman's warbler can be assigned to one of two categoriesthose that are 'definitely extinct', or 'definitely in existence'. Similarly, the number of European bird species extinct since 1600 is surely onenot two, not zero, but one.

Consequently we have an exact, unequivocal answer to the question of how many North American and European bird species have become extinct since 1600. If we could be equally definite for other groups of species, our first step in assessing the mass extinction debate would be complete. Unfortunately, this cut-and-dried situation does not apply to other groups of plants and animals, nor does it apply elsewhere in the worldleast of all in the tropics, where the overwhelming majority of species lives. Most tropical countries have few or no bird-watchers, and no annual monitoring of birds. Many tropical areas have never again been monitored since they were first explored biologically many years ago. The status of many tropical species is unknown, because no one has seen them again or specifically looked for them since they were discovered. For instance, among the New Guinea birds that I study, Brass's friarbird is known only from eighteen specimens shot at one lagoon on the Idenburg River between 22 March and 29 April 1939. No scientist has revisited that lagoon, so we know nothing about the current status of Brass's friarbird. At least, jve know where to look for that friarbird. Many other species were described from specimens collected by nineteenth-century expeditions that provided only vague indications of the collecting site, such as, 'South America'. Try resolving the status of some rare species when you have only that broad hint where to look! The songs, behaviour, and habitat preferences of such species are unknown. Hence we do not know where to seek them, nor how to identify them if we glimpsed or heard them.

The status of many tropical species cannot be classified either as 'definitely extinct' or 'definitely in existence', but just as 'unknown'. Instead, it becomes a matter of chance which species happens to attract the attention of some ornithologist, becomes the object of a specific search, and hence may be recognized as possibly extinct.

Here is an example. The Solomon Islands are another of my favourite bird-watching areas in the tropical Pacific Ocean, and will be recalled by older Americans and Japanese as the site of some of the fiercest fighting in the Second World War. (Remember Guadalcanal, Henderson Field, President Kennedy's PT boat, the Tokyo Express?) The ICBP lists one Solomon bird species, Meek's crowned pigeon, as extinct. Yet when I tabulated all recent observations of all 164 known Solomon bird species, I noticed that twelve of those 164 species had not been encountered since 1953. Some of those twelve species are surely extinct, because they were formerly abundant and conspicuous. Several Solomon islanders told me that those birds had been exterminated by cats. Twelve species possibly extinct out of 164 still may not sound like much to worry about. However, the Solomons are in much better shape environmentally than most of the remaining tropical world, because they have relatively few people, few bird species, little economic development, and much natural forest. More typical of the tropics is Malaysia, which is rich in species and has had most of its lowland forest cut down. Biological explorers had identified 266 fish species dependent on fresh water in Malaysia's forest rivers. A recent search that lasted four years was able to find only 122 of those 266 speciesless than half. The other 144 Malaysian freshwater fish species must either be extinct, rare, or very local. They reached that status before anyone noticed it.

Malaysia is typical of the tropics in the pressure it faces from humans. Fish are typical of all species other than birds, in that they attract only patchy scientific attention. The estimate that Malaysia has already lost (or nearly lost) half of its freshwater fish is therefore a reasonable ballpark figure for the status of plants, invertebrates, and vertebrates other than birds in much of the rest of the tropics.

That is one complication in trying to pinpoint the number of extinctions since 1600: the status of many or most named species is unknown. But there is a further complication. So far, we have been trying to assess the extinction only of those species that had already been discovered and described (named). Could any species have become extinct before they were even described? Of course they could, since sampling procedures suggest that the actual number of the world's species is near thirty million, but less than two million species have been described. Two examples illustrate the certainty of other species becoming extinct before description. Botanist Alwyn Gentry surveyed the plants of an isolated ridge in Ecuador called Centinela, where he found thirty-eight new species confined to that edge. Shortly afterwards, the ridge was logged and those plants were exterminated. On Grand Cayman Island in the Caribbean, zoologist Fred Thompson discovered two new species of land snails confined to forest on a limestone ridge that was completely cleared a few years later for a housing development. The fact that Gentry and Thompson accidentally visited those ridges before rather than after they were cleared means that we have names for those extinct species. But most tropical areas that are being developed are not first surveyed by biologists. There must have been land snails on Centinela, and plants and snails on innumerable other tropical ridges, that we exterminated before we discovered them.

In short, the problem of determining the number of modern species that have become extinct seems at first to be simple and to lead to modest estimatesfor example, only five or six extinct bird species in all of North America plus Europe. On reflection, though, we appreciate two reasons why published lists of species known to be extinct must be gross underestimates of the actual numbers involved. Firstly, by definition the published lists consider only named species, whereas the great majority of species (except in well-studied groups like birds) have not even been named. Secondly, outside North America and Europe and except for birds, the published lists consist only of those few named species which some biologist happened to get interested in for one or another reason and found to be extinct. Among all those remaining species of unknown status, many are likely to be extinct or nearly sofor example, about half in the case of Malaysian freshwater fishes.

Now let's move on to the second step in evaluating the mass extinction debate. Our estimates up to this point have concerned only those species exterminated since 1600 AD, when scientific classification of species was beginning. These exterminations have taken place because the world's human population has grown in numbers, reached previously uninhabited areas, and invented increasingly destructive technologies. Did these factors spring up suddenly in 1600, after several million years of human history? Were there no exterminations before 1600? Of course not. Until fifty thousand years ago, humans were confined to Africa plus the warmer areas of Europe and Asia. Between then and 1600 AD our species underwent a massive geographic expansion that took us to Australia and New Guinea around 50,000 years ago, Siberia around 20,000 years ago, most of North and South America around 11,000 years ago, and most of the world's remote oceanic islands only since 2000 BC. We also underwent a massive expansion in numbers, from perhaps a few million people 50,000 years ago to about half a billion in 1600. Our destructiveness also increased, with the development of improved hunting skills in the last 50,000 years (Chapter Two), polished stone tools and agriculture in the last 10,000 years (Chapters Ten and Fourteen), and metal tools in the last 6,000 years.

In every area of the world that paleontologists have studied and that humans first reached within the last 50,000 years, human arrival approximately coincided with massive instances of prehistoric species' extinction waves. For Madagascar, New Zealand, Polynesia, and the Americas I have described those instances in the preceding two chapters. After people reached Australia, that continent lost its giant kangaroos, its 'marsupial lion', and other giant marsupials. Around the time that Indians reached North America 11,000 years ago, it lost lions, cheetahs, native wild horses, mammoths, mastodonts, giant ground sloths, and several dozen other large mammals. Mediterranean islands like Crete and Cyprus lost dwarf elephants and pygmy hippos, while Madagascar lost giant lemurs and flightless elephant birds. New Zealand lost its giant flightless moas, and Hawaii its flightless geese and dozens of smaller birds, when the Polynesians arrived around 1000 and 500 AD, respectively.

Ever since scientists became aware of these prehistoric extinction waves associated with human arrival, they have argued over whether people were the cause or just happened to arrive while animals were succumbing to climate changes. In the case of the extinction waves on Polynesian islands, there is now no reasonable doubt that Polynesian arrival in one way or another caused them. Bird extinction waves and Polynesian arrival coincided within a few centuries at a time when no big climate change was happening, and bones of thousands of roasted moas have been found in Polynesian ovens. The coincidence of timing is equally convincing for Madagascar. But the causes of the earlier extinction waves, especially those in Australia and the Americas, are still being debated. As I explained on America's extinction waves in Chapter Eighteen, the evidence seems to me overwhelming that humans also played a role in those prehistoric cases of extinction outside Polynesia and Madagascar. In each part of the world an extinction wave occurred after the first arrival of humans, but did not occur simultaneously in other areas undergoing similar climate swings, and did not occur in the same area whenever si rnilar climate swings had occurred previously.

Hence I doubt that climate did it. Instead, all of you who have visited Antarctica or the Galapagos Islands know how tame are the animals there, being unaccustomed to humans until recently. Photographers can still walk up to those naive animals as easily as hunters used to. I assume that the first arriving hunters similarly walked up to naive mammoths and moas elsewhere in the world, while rats that came with the first hunters walked up to naive little birds of Hawaii and other islands.

It is not just in those areas of the world previously unoccupied by humans that prehistoric humans probably exterminated species. Within the last 20,000 years species also became extinct in the areas long occupied by humansin Eurasia, woolly rhinos, mammoths, and giant deer ('Irish elk') died out, and Africa lost its giant buffalo, giant hartebeest, and giant horse. These big beasts may also have been among the victims of prehistoric humans who had already been hunting them for a long time, but who now were able to hunt them with better weapons than ever before. Eurasia's and Africa's big mammals were not unused to humans, but they disappeared for the same two simple reasons that California's grizzly bear, and Britain's bears, wolves, and beavers, succumbed only in recent times, after thousands of years of human persecution. Those reasons were more people, and better weaponry.

Can we at least estimate how many species were involved in these prehistoric extinction waves? No one has ever tried to guess the number of plants, invertebrates, and lizards exterminated by prehistoric habitat destruction, but virtually all oceanic islands explored by paleontologists have yielded remains of recently extinct bird species. Extrapolation to those islands not yet paleontologically explored suggests that about 2,000 bird speciesone fifth of all the birds that existed a few thousand years agowere island species already exterminated prehistorically. That does not include birds that may have been exterminated prehistorically on the continents. Among genera of large mammals, about seventy-three, eighty, and eighty-six per cent respectively became extinct in North America, South America, and Australia at the time of or after human arrival. The remaining step in evaluating the mass extinction debate is to predict the futufe. Is the peak of the extinction wave that we have caused already past, or is most still to come? There are a couple of ways to assess this question.

A simple way is to reason that tomorrow's extinct species will be drawn from today's endangered species. How many species that still exist have populations already reduced to dangerously low levels? The ICBP estimates that at least 1,666 bird species are either endangered or at imminent risk of extinctionalmost twenty per cent of the world's surviving birds. I said 'at least 1,666 , because this number is an underestimate for the same reason I mentioned that the ICBP's estimate of extinct species was an underestimate. Both numbers are based just on those species whose status caught a scientist's attention, rather than on a reappraisal of the status of all bird species.

The alternative way of predicting what is to come is to understand the mechanisms by which we exterminate species. Extinction of species caused by humans may continue accelerating until human population and technology reach a plateau, but neither shows any signs of plateauing. Our population, which grew ten fold from half a billion in 1600 to over five billion now, is still growing at close to two per cent per year. Every day brings new technological advances for changing the earth and its denizens. There are four main mechanisms by which our growing population exterminates species: by overhunting, species introductions, habitat destruction, and ripple effects. Let's see if these four mechanisms have plateaued.

Overhuntingkilling animals faster than they can breedis the main mechanism by which we have exterminated big animals, from mammoths to California grizzly bears. (The latter appears on the flag of California, the state in which I live, but many of my fellow Californians do not recall that we exterminated our state's symbol long ago.) Have we already killed off all big animals that we might kill off? Obviously not. While the low numbers of whales led to an international ban on whaling for commercial reasons, Japan thereupon announced its decision to triple the rate at which it kills whales 'for scientific reasons'. We have all seen photos of the accelerating slaughter of Africa's elephants and rhinos, for their ivory and horns respectively. At current rates of change, not just elephants and rhinos but most populations of most other large mammals of Africa and Southeast Asia will be extinct outside game parks and zoos in a decade or two. The second mechanism by which we exterminate is through intentionally or accidentally introducing certain species to parts of the world where they did not previously occur. Familiar examples of introduced species now firmly established in the US are Norway rats, European starlings, boll weevils, and the fungi causing Dutch elm disease and chestnut blight. Europe too has acquired introduced species, of which the misnamed Norway rat is an example (it originated in

Asia, not Norway). When species are introduced from one region to another, they often proceed to exterminate some of the new species they encounter, by eating them or causing diseases. The victims evolved in the absence of the introduced Pests and never developed defences against them. American chestnut trees have already been virtually exterminated in this way by chestnut b"ght, an Asian fungus to which Asian chestnut trees are resistant. milarly, goats and rats have exterminated many plants and birds on oceanic islands. Have we already spread all possible pests all around the world?

Obviously not; there are many islands still free of goats and Norway rats, and many insects and diseases to try to keep out of many countries by quarantines. The US Department of Agriculture has been trying at great expense, but apparently without success, to forestall the arrival of killer bees and Mediterranean fruit flies. In fact, what will probably prove to be the biggest extinction wave caused by an introduced predator in modern times has just started in Africa's Lake Victoria, home to hundreds of species of remarkable fishes found nowhere else in the world. A large predatory.fish called the Nile perch, intentionally introduced in a misguided effort to establish a new fishery, is now eating its way through the lake's unique fishes. Habitat destruction is the third means by which we exterminate. Most species occur in just a certain type of habitat: marsh warblers live in marshes, while pine warblers live in pine forests. If one drains marshes or cuts forests, one eliminates the species dependent on those habitats just as certainly as if one were to shoot every individual of the species. For example, when all the forest on Cebu Island in the Philippines was logged, nine of the ten birds unique to Cebu became extinct. In the case of habitat destruction, the worst is still to come because we are just starting in earnest to destory tropical rainforests, the world's most species-rich habitats. The rainforests' biological richness is legendaryover 1,500 beetle species living in a single rainforest tree species in Panama, for instance. Rainforests cover only six per cent of the Earth's surface but harbour about half of its species. Each area of rainforest has large numbers of species unique to that area. To mention only some exceptionally rich rainforests now being destroyed, the felling of Brazil's Atlantic forest and Malaysia's lowland forest is already almost complete, and those of Borneo and the Philippines will be mostly logged within the next two decades. By the middle of the next century, the only large tracts of tropical rainforest likely to be still surviving will be in parts of Zaire and the Amazon Basin.

Every species depends on other species for food and for providing its habitat. Thus, species are connected to each other like branching chains of dominoes. Just as toppling one domino in a chain will topple some others, so too the extermination of one species may lead to the loss of others, which may in turn push still others over the brink. This fourth mechanism of extinction may be described as a ripple effect. Nature consists of so many species, connected to each other in such complex ways, that it is virtually impossible to foresee where the ripple effects from the extinction of any particular species may lead.

For example, fifty years ago no one anticipated that the extinction of big predators (jaguars, pumas, and harpy eagles) on Panama's Barro Colorado Island would lead to the extinction there of little antbirds, and to massive changes in the tree species composition of the island's forest. Yet it did so, because the big predators used to eat medium-sized predators like peccaries, monkeys, and coatimundis, and medium-sized seed-eaters like agoutis and pacas. With the disappearance of the big predators, there was a population explosion of the medium-sized predators, which proceeded to eat up the antbirds and their eggs. The medium-sized seed-eaters also exploded in abundance and ate large seeds that had fallen on the ground, thereby suppressing the propagation of tree species producing large seeds and favouring instead the spread of competing tree species with small seeds. That shift in forest tree composition is expected in turn to cause an explosion of mice and rats feeding on small seeds, and then to an explosion in hawks, owls, and ocelots preying on those small rodents. Thus, the extinction of three uncommon species of big predators will have triggered a rippling series of changes in the whole plant and animal community, including the extinction of many other species.

Through these four mechanismsoverhunting, species introductions, habitat destruction, and ripple effectsprobably over half of existing species will be extinct or endangered by the middle of the next century, when this year's crop of human babies reaches the age of sixty. Like many fathers today, I often wonder how I will describe to my twin sons, who are now three years old, the world that I grew up in and that they will never see. By the time they would have been old enough to come with me to New Guinea, one of the world's biological treasurehouses where I have worked for the past twenty-five years, most of New Guinea's eastern highlands will be deforested. When one adds the extinction of species we have already caused to that which we are about to cause, it is clear that the current extinction wave is surpassing the asteroid collision that may have wiped out the dinosaurs. Mammals, plants, and many other types of species survived that collision nearly unscathed, while the current wave is affecting everything from leeches and lilies to lions. Thus, the claimed extinction crisis is neither a hysterical fantasy, nor just a serious risk for the future. Instead, it is an event that has already been accelerating for 50,000 years and will start to approach completion in our children's lifetimes.

Let's finally consider two arguments that accept the reality of the extinction crisis but dismiss its significance. Firstly, is extinction not a natural process anyway? If so, why make a big deal about the wave of extinction happening now?

The answer to this first argument is that the current extinction rate caused by humans is far higher than the natural rate. If the estimate that half the world's total of thirty million species will become extinct in the next century is correct, then species are now becoming extinct at a rate of about 150,000 per year, or seventeen per hour. The world's 9,000 bird species are becoming extinct at a rate of at least two per year, but bird species under natural conditions were disappearing at a rate of less than one per century, so the present rate is at least 200 times the normal rate. Dismissing the extinction crisis on the grounds that extinction is natural would be just like dismissing genocide on the grounds that death is the natural fate of all humans.

The second argument is a simple one: so what? We care about our children, not about beetles and snail darters; who cares if ten million beetle species become extinct? The answer to this argument is equally simple. Like all species, we depend on other species for our existence, in many ways. Some of the most obvious ways are that other species produce the oxygen we breathe, absorb the carbon dioxide we exhale, decompose our sewage, provide our food, maintain the fertility of our soil, and provide our wood and paper.

Then could we not preserve only those particular species that we need, and let other species become extinct? Of course not, because the species we need also depend on other species. Just as Panama's antbirds could not have anticipated their need for jaguars, the ecological chain of dominoes is much too complex for us to have figured out which dominoes we can dispense with. For instance, could anyone please answer these three questions. Which ten tree species produce most of the world's paper pulp? For each of those ten tree species, which are the ten bird species that eat most of its insect pests, the ten insect species that pollinate most of its flowers, and the ten animal species that spread most of its seeds? Which other species do these ten birds, insects, and animals depend on? You would have to be able to answer those three impossible questions if you were the president of a timber company trying to figure out which species you could afford to allow to become extinct.

If you are trying to evaluate some proposed development project that would bring in a million dollars but might exterminate a few species, it is still tempting to prefer the certain profit over the uncertain risk. Then consider the following analogy. Suppose someone offers you a million dollars in return for the privilege of painlessly cutting out two ounces of your valuable flesh. You figure that two ounces is only one-thousandth of your body weight, so you will still have nine hundred and ninety-nine thousandths of your body left, which is plenty. That is fine if the two ounces come from your spare body fat and if they will be removed by a skilled surgeon. But what if the surgeon just hacks two ounces from any conveniently accessible part of your body, or does not know which parts are essential? You might then find that the two ounces came from your urethra. If you plan to sell off most of your body, as we now plan to sell off most of our planet's natural habitats, you are certain eventually to lose your urethra.

To conclude, let's place matters in perspective by comparing the two clouds which, as I mentioned at the outset, are hanging over our future. A nuclear holocaust is certain to prove disastrous, but it is not happening now, and it may or may not happen in the future. An environmental holocaust is equally certain to prove disastrous, but it differs in that it is already well underway. It started tens of thousands of years ago, is now causing more damage than ever before, is in fact accelerating, and will climax within about a century if unchecked. The only uncertainties are whether the resulting disaster would strike our children or our grandchildren, and whether we choose to adopt now the many obvious countermeasures.