Dr. Alan Robock is a professor of climatology in the Department of Environmental Sciences at Rutgers University and the associate director of its Center for Environmental Prediction.
Introduction
Nuclear winter is a term that describes the climatic effects of nuclear war. In the 1980’s, work conducted jointly by Western and Soviet scientists showed that for a full-scale nuclear war between the United States and the Soviet Union the climatic consequences, and indirect effects of the collapse of society, would be so severe that the ensuing nuclear winter would produce famine for billions of people far from the target zones.
There are several wrong impressions that people have about nuclear winter. One is that there was a flaw in the theory and that the large climatic effects were disproven. Another is that the problem, even if it existed, has been solved by the end of the nuclear arms race. But these are both wrong. Furthermore, new nuclear states threaten global climate change even with arsenals that are much less than 1% of the current global arsenal.
What’s New
Based on new work published in 2007 and 2008 by some of the pioneers of nuclear winter research who worked on the original studies, we now can say several things about this topic.
New Science:
* A minor nuclear war (such as between India and Pakistan or in the Middle East), with each country using 50 Hiroshima-sized atom bombs as airbursts on urban areas, could produce climate change unprecedented in recorded human history. This is only 0.03% of the explosive power of the current global arsenal.
* This same scenario would produce global ozone depletion, because the heating of the stratosphere would enhance the chemical reactions that destroy ozone.
* A nuclear war between the United States and Russia today could produce nuclear winter, with temperatures plunging below freezing in the summer in major agricultural regions, threatening the food supply for most of the planet.
* The climatic effects of the smoke from burning cities and industrial areas would last for several years, much longer than we previously thought. New climate model simulations, that have the capability of including the entire atmosphere and oceans, show that the smoke would be lofted by solar heating to the upper stratosphere, where it would remain for years.
New Policy Implications:
* The only way to eliminate the possibility of this climatic catastrophe is to eliminate the nuclear weapons. If they exist, they can be used.
* The spread of nuclear weapons to new emerging states threatens not only the people of those countries, but the entire planet.
* Rapid reduction of the American and Russian nuclear arsenals will set an example for the rest of the world that nuclear weapons cannot be used and are not needed.
How Does Nuclear Winter Work?
A nuclear explosion is like bringing a piece of the Sun to the Earth’s surface for a fraction of a second. Like a giant match, it causes cities and industrial areas to burn. Megacities have developed in India and Pakistan and other developing countries, providing tremendous amounts of fuel for potential fires. The direct effects of the nuclear weapons, blast, radioactivity, fires, and extensive pollution, would kill millions of people, but only those near the targets. However, the fires would have another effect. The massive amounts of dark smoke from the fires would be lofted into the upper troposphere, 10-15 kilometers (6-9 miles) above the Earth’s surface, and then absorption of sunlight would further heat the smoke, lifting it into the stratosphere, a layer where the smoke would persist for years, with no rain to wash it out.
The climatic effects of smoke from fires started by nuclear war depend on the amount of smoke. Our new calculations show that for 50 nuclear weapons dropped on two countries, on the targets that would produce the maximum amount of smoke, about 5 megatons (Tg) of black smoke would be produced, accounting for the amount emitted from the fires and the amount immediately washed out in rain. As the smoke is lofted into the stratosphere, it would be transported around the world by the prevailing winds. We also did calculations for two scenarios of war between the two superpowers who still maintain large nuclear arsenals, the United States and Russia. In one scenario, 50 Tg of black smoke would be produced and in another, 150 Tg of black smoke would be produced. How many nuclear weapons would be required to produce this much smoke? It depends on the targets, but there are enough weapons in the current arsenals to produce either amount. In fact, there are only so many targets. Once they are all hit by weapons, additional weapons would not produce much more smoke at all. Even after the current nuclear weapons reduction treaty between these superpowers is played out in 2012, with each having about 2,000 weapons, 150 Tg of smoke could still be produced.