For example, following a nuclear exchange between India and Pakistan, employing just 100 such nuclear weapons, uncontrollable fires burning in ruined cities on the Indian sub-continent would, over a period of days, loft a mass of soot into the upper atmosphere, which was estimated to be as large as 5 million tons.
The climate model showed that this large mass of soot would be distributed within weeks over the entire northern hemisphere, and then more slowly over the southern hemisphere. Within months, global temperatures were seen to fall as much as 1.3 degree C, with a recovery time calculated to be as long as ~10 years.
The consequences for agriculture of a global fall in temperatures of 1.3 degree C, extending over at least a several year period, were considered to be dire. A global decrease in the available food supply was estimated to be as large as 20%. Under such conditions, it was said, starvation would be widespread, especially in the third world, and casualties due to famine would probably far exceed those due to the direct effects of nuclear weapons; e.g., possibly as many as 1 billion people would die from starvation, whereas the number of prompt deaths due to blast, fire, and radiation were expected to exceed tens of millions of people.
The climate model was the state-of-the-art general circulation model, ModelE, from the NASA Goddard Institute for Space Studies, which included a module to calculate the transport and removal of aerosol particles. It is able to represent the atmosphere up to a height of 80 km, and simulates plume rise to the middle and upper stratosphere, producing a long aerosol lifetime. The atmospheric model was connected to a full ocean general circulation model, with simulated sea ice, allowing the ocean to respond quickly at the surface and on yearly time scales in the deeper ocean.
This work was a continuation of well-known past work, circa 1985, describing so-called nuclear winter scenarios. In that work, nuclear exchanges between the USSR and the USA were found to cause large decreases in global temperatures, lasting for long periods of time. But, it is now thought that these scenarios actually underestimated the climatic effects of large-scale nuclear exchanges, due to inadequate simulation of the degree to which soot would be lofted into the upper atmosphere. [Crutzen, P. J. and Birks, J. W.: The atmosphere after a nuclear war: Twilight at noon, Ambio, 11, 114–125, 1982; Turco, R. P., Toon, O. B., Ackerman, T. P., Pollack, J. B., and Sagan, C.: Nuclear winter: Global consequences of multiple nuclear explosions, Science, 222, 1283–1292, 1983; Pittock, A. B., Ackerman, T. P., Crutzen, P. J., MacCraken, M. C., Shapiro, C. S., and Turco, R. P.: Environmental Consequences of Nuclear War SCOPE-28, Vol. 1, Physical and Atmospheric Effects, Wiley, Chichester, England, 1985 (Second ed. 1989).]
Using improved models for soot transport, changes of global climate following a nuclear exchange between the USSR and the USA of a combined total of 1750 Mt of TNT equivalent, over a period of one week, was simulated. This scenario involved the injection of 50 million tons of soot into the upper atmosphere and, following an initiation period of a few months, led to reductions in global temperature of 3.5 degree C, lasting for ~3 years, decreasing to ~1.5 degree C after 10 years. [Nuclear winter revisited with a modern climate model and current nuclear arsenals, A. Robock, L. Oman, and G. L. Stenchikov, J. of Geophys. Research, Vol. 112, D13107, doi:10.1029/2006JD008235, 2007.]
The extraordinary results obtained from these simulations have been public information now for 6 years. However, the amount of media discussion that has been provoked is minimal. Insofar as USA national policy is concerned, public attention today is fixed instead on other important matters such as unemployment, the budget deficit, the Affordable Care Act, and the so-called "nuclear option" in the US Senate.
Although the media are also very much interested in the ongoing struggle with Iran over its enrichment of uranium, and its construction of a heavy water nuclear reactor which will enable it to produce plutonium, little or no energy is being spent on contemplation of the looming disaster represented by the remnant ~5,000 nuclear weapons in each of the arsenals of the USSR and the USA, and the 100's of nuclear weapons possessed by England, France, China, India, Pakistan, and Israel.
I agree that allowing the number of members of the nuclear club to increase represents a present danger to us all. However, the retention of ~10,000 nuclear weapons in the arsenals of the established nuclear weapons club members is, I believe, an even bigger threat.
Somehow, it must be possible to so stigmatize the use of nuclear weapons, that even their possession will ultimately be deemed unacceptable by the world's people. If the USA does not lead the way to the abolition of nuclear weapons, then what nation will?
The Nuclear Non-Proliferation Treaty will be up for review in 2015, but signs for the continuation of effective prohibitions on the development of nuclear weapons, by non-nuclear weapons states, are not good. Many nations of the world are unhappy with the lack of significant progress toward the abolition of nuclear weapons, promised for the last 40 years by members of the nuclear weapons club.
It seems altogether right then that the USA should attempt to break through this logjam of fatalism and distrust by drastically, and if needs be unilaterally, reducing the numbers of nuclear weapons in its own arsenal; e.g., to well below 1000 nuclear weapons.
It seems right too that the USA should set an example by stopping the development of new technologies geared toward the extension of the lifetimes of its stockpiled nuclear weapons and, above all, by ending research focused on accumulating more knowledge of the science and engineering of nuclear weapons; i.e., such knowledge which may enable the creation of a new generation of still more destructive nuclear weapons.
The USSR, under M. Gorbachov, showed the world that Cold War hostilities could be checked, and for a while reversed. Now it's up to the USA to play an essential role in the reduction of global tensions. If left to fester, these tensions, along with developing new nuclear weapons technologies may, in my opinion, lead eventually to the extermination of us as a species.
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