READERS WILL recall debates held in the 1980s on the global nuclear winter projected to follow all-out nuclear war between Russia and America. Nuclear winter was estimated to be severe enough to wipe out human civilisation and this lead to worldwide demand for nuclear disarmament, writes WILLIAM REVILLE
You might think that the probability of nuclear winter has all but disappeared now that the Cold War has ended. Unfortunately not. Nuclear arsenals have grown in many countries and the prospect of regional nuclear conflicts is all too real. Recent calculations, described by Alan Robock and Owen B Toon in Scientific American, January 2010, demonstrate that even a regional nuclear war could precipitate global nuclear winter.
Nuclear winter, you will recall, develops as follows. Nuclear explosions ignite massive fire-storms, causing smoke to rise high into the atmosphere to be carried around the globe. This smoke blots out the sun, causing darkness and permanent freezing. Plants cannot grow, food production quickly fails and billions die. Civilisation is destroyed and, possibly, all humans die. This scenario has been carefully studied and nuclear winter is the mature prediction of mainstream science.
Since the end of the Cold War, America and Russia have greatly reduced their arsenals, but they still retain considerable nuclear weaponry. Nine countries have nuclear weapons and they are ranked as follows in order of the number of warheads they possess: Russia (15,000), US (9,900), France (350), China (200), UK (200), Israel (80), Pakistan (60), India (50), North Korea (10+). In addition, Iran may be developing nuclear weapons.
There is a real possibility of nuclear war between India and Pakistan and Robock and Toon have evaluated the consequences. They assume that such a war would quickly escalate out of control, with the deployment of full nuclear arsenals on both sides. They reason as follows: Pakistan is a small country and could be easily overrun and immobilised by Indian conventional forces. Pakistan would be tempted to release its nuclear arsenal before being overrun and India would respond in kind. They assume that each side would drop 50 bombs on major cities and industrial areas – each about the size of the one dropped on Hiroshima in 1945.
The authors estimate that 20 million would die immediately from direct blast, fire and radiation. Seven million metric tons of smoke would then rise up through the atmosphere (troposphere) and into the lower stratosphere. Within five days the smoke would cover the war region, within nine days it would reach around the globe, and within 49 days it would cover the inhabited earth.
Smoke from nuclear fires would stay aloft for 10 years and would block enough sunlight to maintain overcast conditions everywhere. Climate models forecast that this smoke would quickly cool the earth to below temperatures experienced for the past 1,000 years.
According to the authors these changes would play havoc with agricultural production and big drops in crop yields would occur everywhere. Panic would cripple the global agricultural system. About one billion people worldwide live on marginal food supplies and they could die from famine.
The nuclear winter envisaged in the 1980s in the aftermath of nuclear war would destroy civilisation and possibly eliminate the human race. A nuclear winter after a regional war would be less calamitous in scale. But it would set civilisation back 100 years and this is to assume that social order is maintained and that all we would have to recover from is environmental degradation. But, of course, social order could break down leading to chaos, with God knows what results. The authors put it plainly when they say: “The only way to eliminate the possibility of climatic catastrophe is to eliminate the nuclear weapons.”
William Reville is associate professor of biochemistry and public awareness of science officer at UCC – understandingscience.ucc.ie