Those of us who were involved in peace activities in the 80's probably remember a good deal about nuclear winter. Those who have become involved later may have heard little about it. No scientific study has been published since 1990, and very little appears now in the peace or nuclear abolition literature. It is still important. With thousands of rocket-launched weapons at "launch-on-warning," any day there could be an all-out nuclear war by accident. The fact that there are only half as many nuclear bombs as there were in the 80s makes no significant difference. Deaths from world-wide starvation after the war would be several times the number from direct effects of the bombs, and the surviving fraction of the human race might then diminish and vanish after a few generations of hunger and disease, in a radioactive environment.The concept of Nuclear Winter
Bombs directed at missile silos would burst at ground level and throw a huge amount of dust into the atmosphere, as the explosion of a volcano does. It is as much as a million tonnes from a large nuclear bomb bursting at ground level. Bombs bursting over cities and surface installations, like factories or oil stores and refineries, would cause massive fires and fire-storms that would send huge amounts of smoke into the air. The 1980s research showed that the dust and the smoke would block out a large fraction of the sunlight and the sun's heat from the earth's surface, so it would be dark and cold like an Arctic winter. It would take months for the sunlight to get back to near normal. The cloud of dust and smoke would circle the northern hemisphere quickly. Soon it could affect the tropics, and cold would bring absolute disaster for all crops there. Quite likely it would cross the equator and affect the southern hemisphere to a smaller degree.
While the temperature at the surface would be low, the temperature of the upper part of the troposphere (5-11 km) would rise because of sunlight absorbed by the smoke, so there would be an absolutely massive temperature inversion. That would keep many other products of combustion down at the levels people breathe, making a smog such as has never been seen before. Pyrotoxins is a word coined for all the noxious vapors that would be formed by combustion of the plastics, rubber, petroleum, and other products of civilization. It is certain that these poisons would be formed, but we do not have quantitative estimates. The amount of combustible material is enormous, and it would produce dioxins, furans, PCBs, cyanides, sulphuric and sulphurous acids, oxides of nitrogen, carbon monoxide and carbon dioxide in amounts that would make current concerns about atmospheric pollution seem utterly trivial. There would also be toxic chemicals like ammonia and chlorine from damaged storage tanks.
Another bad environmental thing that would happen is destruction of the ozone layer. The reduction in the ozone layer could be 50% - 70% over the whole northern hemisphere - very much worse than the current losses that we are properly concerned about. Nitrogen oxides are major chemical agents for this. They are formed by combination of the oxygen and nitrogen of the air in any big fire and around nuclear explosions, as they are on a smaller scale around lightning flashes. So after the smoke cleared and the sun began to shine again, there would be a large increase of ultraviolet radiation reaching the earth's surface. This is bad for people in several ways, but don't worry about skin cancer: not many of the survivors would live long enough for that to matter. The ultraviolet radiation is also bad for many other living things, notably plankton, which is the bottom layer of the whole marine food chain. There would likely be enough ultraviolet radiation to cause blindness in many animals. Humans can protect their eyes if they are aware of the danger. Animals do not know how to do that, and blind animals do not survive. Blind insects do not pollinate flowers, so there is another reason why human crops and natural food supplies for animals would fail.
Altogether, nuclear winter would be an ecological disaster of the same sort of magnitude as the major extinctions of species that have occurred in the past, the most famous one being 65 million years ago at the Cretaceous extinction. Of all the species living at the time, about half became extinct. The theory is that a large meteor made a great crater in the Gulf of Mexico, putting a trillion tons of rock debris into the atmosphere. That is a thousand times as much rock as is predicted for a nuclear war, but the soot from fires blocks sunlight more effectively than rock debris. In nuclear winter there would also be radioactive contamination giving worldwide background radiation doses many times larger than has ever happened during the three billion years of evolution. The radiation would notably worsen things for existing species, though it might, by increasing mutations, allow quicker evolution of new species (perhaps mainly insects and grasses) that could tolerate the post-war conditions. (I should just mention that there is no way the radioactivity from a nuclear war would destroy "all life on earth." People must stop saying that. There will be evolution after a war, but it may not include us).Governments did not like the idea of Nuclear Winter
The prediction of nuclear winter was published by a group headed by Carl Sagan in 1983. The initials of their names were T-T-A-P-S, so the paper and their book has become known as "t-taps." It caused some alarm in government circles in USA and NATO countries, not so much because this further disaster would follow a nuclear war, but because of the boost it gave to the Peace Movement. A number of studies were published in the next few years, including major reports by The Swedish Academy of Sciences (Ambio), the International Council of Scientific Unions (SCOPE), and the U.S. National Research Council. There was a drive by government and the military establishment to minimize the matter, and after a few years the media were talking about "nuclear autumn." (The most astonishing lies were propagated, e.g. that Carl Sagan admitted that his publication was "a propaganda scam.") It was true that islands and coastal areas would have less severe temperature drops than the original predictions, because of the modifying effect of the ocean. They would have violent storms instead, because of the big temperature difference between land and water.
In 1990 another paper was published by the T-TAPS group reviewing in detail the later studies, and showing that some modifications to their 1983 paper were necessary. Some of these were in the direction of more severe changes, others towards milder changes. The general picture was little changed. The book, A Path Where No Man Thought by Sagan and Turco (one of the T's), also published in 1990, gives an account of current conclusions for the serious non-specialist reader. It gives detailed descrip-tions of nuclear winters of different severity according to how many weapons were used, and against what targets. If oil refineries and storage were the main targets, 100 bombs would be enough to cause a nuclear winter, and the smallest sizes of nuclear bombs would be effective in starting the fires.A new study needed
Nuclear Winter seems to be a matter that the peace movement has largely forgotten about, and the general public has completely forgotten about. I feel sure we ought to be reminding the world of it. A new scientific study is surely warranted by now. Computer modeling is a main tool in atmospheric research, and the capacity of computers available to university scientists and in government laboratories has increased very much in the last ten years; other atmospheric research has not been dormant. The advances need to be applied. If a new study happened to show that the aftermath of nuclear war would not include severe changes in the weather and climate it would be great news for the nuclear weapon establishments, and slightly good news for those who are working for elimination of nuclear weapons, but we should carry on just the same. If, as seems more likely, the new study largely confirmed the T-TAPS results it would strengthen our position in dialogue and provide a focus for a publicity campaign to re-awaken the voting public to the need to eliminate nuclear weapons, and the urgent need to de-alert them.
An important area where more information is needed is to show whether spread of the cold is likely to affect the tropics. A new study could be expected to add valuable information. Many developing countries have such serious problems of violence, military spending, and sickness, that we can hardly expect the activists there to spend much of their effort in the necessary task of uniting the world to urge the nuclear weapons states to eliminate their weapons. If it were shown that frost is likely to reach tropical latitudes in the event of a nuclear war in the northern countries, scientists and governments in the tropics would know it would be an ecological disaster for themselves. Even a fall of temperature to 10[[ordmasculine]] Celsius destroys a rice crop.
I should emphasize that this is not a question of preventing "proliferation." The weapons that pose the danger of nuclear winter are the existing big arsenals. It is these that need most urgently to be eliminated. A war between Pakistan and India with the arsenals they are believed to have at present, or the use of the few weapons that a "rogue state" might make clandestinely, would be a regional disaster of the most terrible magnitude, but it would not cause nuclear winter.
Efforts are being started to interest atmospheric scientists and to solicit funding for a new study.