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Thank you very much, Mr. Arnelle. I'm delighted to be here. There cannot be many organizations on the planet that have had both Alexander Kerensky and Nikita Khrushchev addressing them, and I'm delighted to have a chance to talk with you. I would much prefer to be talking about the topic that Mr. Arnelle mentioned in the beginning of his introduction, namely the possible opportunities the United States, the Soviet Union and the rest of the nations on the planet, in exploring our local swimming hole in space. But I feel that there is an even more urgent topic that I would like to discuss with you, namely, the nuclear sword of Damocles which is hanging by a thread over our heads and about which we have a remarkable opportunity in this generation to make some major and significant changes.

I want to talk to you about nuclear winter, the surprising and unexpected recent discovery that even a relatively small nuclear war may be capable of producing a global climatic catastrophe. And I want to talk just a little bit about the idea of nuclear winter and then something about its implications for policy and what is called doctrine. When it became clear that nuclear winter was a real possibility and that it had what seemed to me significant policy implications, being a newcomer to this field, I felt it was important to talk to senior practitioners of dark arts and see how they would respond to this. And so, an informal meeting was arranged in Washington, in fact, in the capitol, which had some very distinguished figures there, Avrell Harriman and many others. And I presented the ghastly consequences, long-term consequences of nuclear war, which were emerging then from our computer modeling, and went through some of the policy implications, which I will do here for you as well. After I was done with all this, one senior practitioner said that if I thought that the mere prospect of the end of the world was enough to change policies in Washington and in Moscow, I clearly had not much experience in those two cities.

Therefore, bearing in mind this sympathetic criticism, I have to say I'm really delighted at the extent to which nuclear winter has entered the debate on nuclear policy, and not just in the United States and in the Soviet Union, but increasingly worldwide. Okay, so nuclear winter. What is it, how certain is it and so what? Everybody knows nuclear war is bad and for a lot of people their capacity for horror has already been fully saturated by the prompt effects of nuclear war, and telling them that there are catastrophic long-term effects does not rouse much additional concern, since all the concern that's in a lot of people has already been roused or at least that's what some people say.

The prompt effects of nuclear war are well known: the blast, heat, the prompt radiation, mainly neutron and gamma rays, the plumes of poisonous radioactive fallout that have blown downwind of targets. The World Health Organization estimates that in a major nuclear war some 1.1 billion people would be killed outright - 1.1 billion human beings. And another 1.1 billion people would also die if they did not receive prompt medical attention. But, of course, this is extremely unlikely, since the doctors in the hospitals are almost entirely concentrated at the targets. So the prompt effects have a real prospect of killing something like, if you wish to believe the World Health Organization, something like two billion people, almost half the human inhabitants of the planet. And it's certainly not hard to understand that many people think that's bad enough.

What our group has done is to try and calculate for a very wide range of nuclear war scenarios what the longer-term consequences would be. Mainly, we are talking about the attenuation of sunlight by dust and especially smoke from the burning of cities that would follow in the weeks and months after a nuclear war. But also such questions as the depletion of the ozone protective shield, which protects us against ultraviolet radiation from the sun and the generation of clouds of poisonous gases from the burning of modern cities. In our baseline case, we imagined a 5,000-megaton war. There are something like 13,000 megatons in the combined arsenals of the United States and the Soviet Union. Let me try to give a sense of what these arsenals are.

The global arsenals contain the explosive equivalent of one million Hiroshima bombs. In terms of the energy expended in explosives in the Second World War, you could have a World War II every second for the length of a lazy afternoon before you would exhaust the horrendous power of these global nuclear arsenals. Our baseline case was somewhere between a half and a third of the present nuclear arsenals, but we covered a very large range of possible cases as I mentioned. In this baseline case there was both counter-force and counter-value targeting, that is, targeting against the adversary's retaliatory capability, hardened missile silos, command and control facilities, organizations of national leadership, submarine refurbishing facilities, and the like. But also counter-value attacks in which cities are burned. Both sides claim that they don't intend to target cities, that they're good guys. But it just happens there's this awkward fact that there's a remarkable co-location or proximity of strategic targets with cities. So, in a nuclear war in which only military targets are intended, nevertheless it is very clear and has been repeatedly confirmed by testimony of those who know, including former officials of the Joint Strategic Target Planning Staff, that lots of cities would be destroyed in nuclear war.

Human beings have concentrated burnable materials in the places that they mainly live. And so a nuclear war would produce enormous clouds of dark city smoke, which would rise, merge and spread first in longitude and then in latitude. Even high-yield ground bursts at hardened targets in which, let us imagine, not a single blade of grass is burned would also inject fine dust particles into the stratosphere of the Earth.

In typical cases - in our baseline scenario, for example - we find that the attenuation of sunlight, averaged over the Northern Hemisphere, is down to something like 1 percent sunlight transmitted. That is, at noon it is as dark as - what's a local analogy - Muir Woods at twilight. And the temperature then falls because, after all, it is the sunlight which heats the surface of the Earth, and there is an effect, which I will not go into, in which the greenhouse effect is, in effect, turned off.

Temperatures drop - different people make different estimates - but we estimate ten, 20, 30, 40 degrees on hemispheric average. I point out this is a very large temperature drop. The 1815 explosion of the Indonesian volcano Tambora produced less than a one-degree temperature drop hemispheric average, and that was enough for the following summer to be called "1800 and froze to death." In New England and in Europe it was called "the year without a summer." A one-degree average Northern Hemisphere temperature drop is enough to eliminate most wheat growing in Canada. A typical ice age temperature is something like eight degrees less than the current ambient temperature. So if we were talking about 10, 20, 30, 40 degrees, we're talking about extraordinary temperature declines larger than any since the tenure of humans on the planet Earth.

Now, not only major nuclear wars involving a third, or a half or two-thirds of the strategic arsenals can produce nuclear winter, but much smaller wars can also, we calculate. By the way, "we" is a group of five of us who are mainly planetary scientists who got into this by a most circuitous and accidental route and let me mention who the others are. They're all Californians except myself. I'm also partly a Californian and lived here for some years in the '60s. Richard Turco from Marina Del Rey, California, and from the NASA Ames Research Center, down the Peninsula. Brian Toon, Tom Ackerman, and Jim Pollack.

As I was saying, much smaller nuclear wars we calculate can produce major nuclear winter effects and we calculate that a nuclear war, with less than 1 percent of the strategic inventories will do it, provided cities are targeted. You burn a hundred downtowns and it looks as if you generate nuclear winter. The prevailing wisdom used to be that nuclear war conducted at northern mid-latitudes would have its effects confined to northern mid-latitudes. But we now discover that the heating of the fine, dark particles aloft propels them into the Southern Hemisphere with the consequence that nuclear winter is almost certainly a global, not a regional, effect.

Now, if you imagine all of these put together: the infrastructure of the society utterly destroyed by the prompt effects, billions of people wiped out immediately, the civic and sanitary services, medical facilities, water, electricity, communication, transportation all wiped out. The sun, in effect, turned off. The temperatures dropping much more than they do in winter, although winter is enough. Water supplies frozen to a depth of meters. A deadly smog of poison gases spreading out over the countryside. Radioactive fallout in dangerous quantities, dangerous enough to compromise the human immune system, falling over most of the Northern Hemisphere. The destruction of agriculture and food supplies. The inability to grow a new harvest. With the effects, as I say, propagating into equatorial and Southern Hemisphere regions, you have a ghastly, grizzly picture of what is in store for us if we are so foolish as to permit a nuclear war, even a small one, to occur.

Now, a group of distinguished biologists, some 20 of them, have examined the biological consequences of such a nuclear war, of such a nuclear winter with an eye towards the fragility of the global ecosystem, and conclude that under the circumstances that I've just described, massive species extinctions, not just deaths but extinctions, wiping out every last member of the given species, are likely. And, if you think of the interrelatedness of life on the planet, how dependent we are on plants and animals, to say nothing of industries that most of us never even see, you have some sense of how in the years, decades and centuries following such a nuclear war, the human community might dwindle first to a medieval kind of subsistence level and then back to still earlier levels with the human population falling to prehistoric values and the biologists emphasize that the extinction of the human species cannot be excluded under these circumstances.

Now, this is serious stuff. Extinction is forever. Extinction undoes the lives, makes pointless the lives of all of our ancestors, of everyone who came before us, of all of those 40,000 generations of humans whose accomplishments we are the beneficiary of. And it also undoes the lives of all those humans who might come after us if we do not permit nuclear war to occur. I claim that there is a new set of stakes that nuclear winter has introduced. The stakes are simply much higher than was ever realized before. Now, how certain are these results?

Briefly, the National Academy of Sciences in a recent report says that nuclear winter is at least a "clear possibility." There has been a lot of debate about whether the temperature decline is ten degrees or 20 degrees or 30 degrees, but I stress that an ice age has a typical temperature decline of some six or eight degrees. Now, if you are faced with even a small probability of an absolutely major disaster, you take steps. If the floodwaters are rising and the levees and dams are clearly insufficient, you do not say the probability of a massive flood is, I guess, small, so I will ignore this subject. If there is even a small chance of a major catastrophe, you take steps. Insurance companies know this very well; actuarial statistics work along these lines exactly. You don't say I have nothing to worry about because there's only a small probability of the undesired event. You say, how improbable is the event, how bad would it be, and it's the multiplication of those two factors that determines what insurance premium you're willing to pay. If there is a very small chance that your house will be washed away, at the very least you take a suitable insurance policy and if you're wise, you encourage the local officials to start refurbishing levees and dams. That is, I maintain, the situation that faces us here.

Let me first indicate a few of the consequences for policy and doctrine of nuclear winter. Consider first the issue of first strike. First strike is something which has propelled the arms race, has captivated the attention of strategists on both sides, and, indeed, terrified both the United States and the Soviet Union. Each of them is absolutely petrified that the other will one day, in a slowly escalating crisis or in a bolt from the blue, attempt to strategically disarm the adversary by making a massive strike against their retaliatory capability.

Now, this concern on some level is misplaced because both sides have an invulnerable retaliatory capability as it is. Submarines will survive a first strike. Aircraft aloft will survive a first strike, enough of them, at any rate, to provide an absolutely devastating response after a first strike. But, consider the implications in nuclear winter for first strike, what does it say? Suppose you have two countries, country A and country B, never mind who they are. And country A, for whatever reason, inadvertence or malice, launches a devastating first strike against the land-based strategic arm of its adversary and suppose that country B, for whatever reason, does not retaliate, does not defend itself, simply sits there and takes it. What happens? What happens is that an immense cloud of soot and dust rises over country B, is carried in something like ten days by the prevailing winds halfway around the planet, and nuclear winter ten days later then visits its devastation on the aggressor nation. Justice is done through the global circulation. It does not depend on exigencies and the psychology of the leaders of the adversary nation. Now, if this is true and if it is recognized as true equally by both the United States and the Soviet Union, it has a very mollifying effect on the contentious superpowers. If they are aware that they will suffer from their own first strike to the tune of national devastation, this should, one would hope, moderate the hotheads on both sides.

We've heard a lot about crisis relocation and civilian shelters, the idea that we will leave the cities and go to a benign and receptive countryside where people will welcome us. And then, a few weeks later when the effects are over, kiss our hosts and tell them we'll write and go back to where we came from. But nuclear winter lasts, as far as we can tell, for months. There are some possibilities it may last for years, and if this crisis relocation ever made sense, which I strongly doubt, it surely no longer makes sense in the light of nuclear winter. And, the same is true for civilian shelters, especially in target areas. Think of what the shelter would have to provide compared to what the nominal contemporary shelters do to hold even a small group for the month or years until nuclear war is over, until nuclear winter is over.

Now another major consequence has to do with other nations, nations far removed from the northern mid-latitude target zone, nations that might have thought they could sit this one out and let the two superpowers wipe each other out, and then these other nations might inherit a planet freed of the uncomfortable presence of these nations that smaller nations feel push them around. Well, that also is an untenable view. You cannot any longer imagine catching an Air New Zealand flight at a time of high crisis. And, as a result, you find in the last year or two a remarkable concern among nations that are unlikely to be nuclear targets about the consequences of nuclear war. Those nations can be utterly destroyed without a single nuclear weapon dropping on their territories. And so, the stakes of nuclear war, as perceived, have now become worldwide, and that is a new element in what the United States and the Soviet Union will have to deal with if they continue their present policies, and my guess is that we will see this to be an increasingly effective leverage force on the major nuclear powers.

Now, you might ask yourself what happens if one nation believes in nuclear winter and the other doesn't. That is, what about an asymmetry of perception, as it is called in the nuclear strategy business, which has, as a major sub-industry, the generation of phrases and acronyms which put emotional distance between the speaker and the subject. An asymmetry of perception, I like to call it a fear gap. What happens if Americans are afraid of nuclear war and Russians aren't? This argument has been used to say, well, let's keep the facts of nuclear war from Americans so that we will not have a fear gap. But it turns out that the Soviet Union has widely reported the results - both of American and of their own scientists - on nuclear winter there have been extensive discussions on Soviet television, in Izvestiya and Pravda and so on. It turns out there is enough fear to go around.

Another question which nuclear winter raises is, What else have we missed? It took almost 40 years from the first nuclear explosion for people to tumble to the fact that nuclear winter was a - I'll use the National Academy's phrase - clear possibility in the wake of nuclear war. Why did it take so long? There are vast establishments in the United States and the Soviet Union and other nations with annual budgets and hundreds of millions and billions of dollars whose job it is to inform national leaders on the consequences of nuclear war. These organizations simply failed. We can talk about why they failed, some people have some ideas, but the main fact is that they failed. And this then raises another very awkward question. What else have we missed? Nuclear war has never happened except for the abortive nuclear war at the end of the Second World War, which used up all the nuclear weapons that existed at the time. We do not have experience with nuclear war. We see that at least one, and in fact, I will argue three or four major effects have been missed. What else has been missed? Whatever it is, we can be reasonably certain that it will not be something that ameliorates the consequences of nuclear war; it will be something that makes things still worse. There is a kind of arrogance that supposes that everything we know is all there is to know, particularly when the stakes are as high as in nuclear war.

Well, I want to draw to a conclusion. I would like to ask you to consider the present arsenals with 55,000 nuclear weapons, with 18,000 of those nuclear weapons in delivery systems which can take them thousands of miles, halfway around the world, to visit instant devastation on human beings on the other side of the planet. Fifty-five thousand nuclear weapons. A single U.S. nuclear submarine can destroy 160 Soviet cities. One submarine sitting silent, undetected, in the ocean depths. But the United States has some 30 such submarines. The Soviet Union has a roughly comparable amount. There are the bomber forces of the two nations: the strategic intercontinental missiles; the intermediate range missiles; cruise missiles; munitions; nuclear weapons fired out of cannons; depth charges; nuclear armed mines; suitcase nuclear weapons, which for all we know are sitting in the embassies all over the world in a basement waiting for orders. Is this a rational way to organize the planet?

If you were a Martian and came to the Earth and knew nothing about the past history of argumentation and dispute among the various contending powers but only knew that here was a nation, a planet that had reasonable people, they were able to build things; they were reasonably smart; they were apparently concerned about their own future. And yet, on this planet, they spend one trillion dollars a year on armaments, while people are starving all over the planet. And they have amassed a grotesque and bloated arsenal of nuclear weapons capable of destroying their global civilization surely, and at least possibly their species. And their response to this is to add each year to this arsenal. What would you think of them? Would you think that they knew what they were doing? Would you think that they truly had their own best interest in mind? I don't think so. I think you would conclude that this was a species that might be smart in some small areas, but in what really counts, they had simply missed the main point.

If we are content with world inventories at this level - ten or a hundred times more than can initiate nuclear winter - we are saying that it's safe to trust the fate of our global civilization and, perhaps, our species to all leaders, civilian and military, of all present and future nuclear powers, and to the command and control efficiency and technical reliability in those nations now and into the indefinite future. We are risking, we are betting our lives on the competence of Soviet computers, among other things. For myself, I would far rather have a world in which the climatic catastrophe cannot happen independent of the vicissitudes of leaders, institutions and machines, independent of the possibility of machine failure and miscommunicated orders and madness in high office. This seems, to me, elementary national patriotism as well as elementary planetary hygiene. There are too many nuclear weapons in the world - they serve no useful purpose. If you like the idea of a mutually assured destruction, a strategic retaliatory force, which discourages the other side from doing something stupid, you can maintain that retaliatory capability at a tiny fraction of the present arsenals. Why do we have so many nuclear weapons in the world? What we clearly have to do is to arrange for a massive, bilateral, verifiable reduction in these instruments of death.

The problem cries out for an ecumenical perspective that rises above "can't" and doctrine and mutual recrimination, however apparently justified, and that at least partly transcends our parochial fealties in time and space. What is urgently required is a coherent, mutually agreed upon, long-term policy for dramatic reductions in nuclear armaments and a deep commitment embracing decades to carry it out. There are no technical difficulties. This is a matter of political will. Our talent, while imperfect, to foresee the future consequences of our present actions and to change our course appropriately is a hallmark of our species. It's one of the chief reasons for our success over the past few million years. Our future depends entirely on how quickly and how broadly we can refine this talent to foresee the future consequences of present actions.

We should plan for and cherish our fragile world as we do our children and our grandchildren. Indeed, there will be no other place for most of them to live. It is nowhere ordained that we must remain in bondage to nuclear weapons forever. Thank you very much.

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