A VERY important digression

For some obscure reason, many people have come to believe that the Nuclear Winter hypothesis promulgated by Carl Sagan and colleagues back in the 1980s has been discredited. It has not.

Nevertheless, people might be inclined to think that with the end of the cold war and the immediate confrontation between the U.S. and the Soviet Union, the threat of nuclear apocalypse has disappeared. It has not. Alan Robock and Owen Brian Toon calculate that an all out nuclear war between India and Pakistan, using the arsenals they currently possess, would bring about an unimaginable catastrophe.

As the cities of the subcontinent burned, smoke would rise into the stratosphere, above the level where rain can wash it out, and persist there, blocking the sun, for years. As a result, average temperatures in mid-summer in the temperate zones would remain below freezing for five years. As you can imagine, the result would be the extermination of most species of plants and animals, and at least the near-extermination of humanity and the destruction of civilization.

The fact is that India and Pakistan are currently quite hostile and there is a very dangerous state of tension between them including surrogate conflict in Afghanistan and a guerrilla movement of Kashmiri irredentists which includes factions that use terrorist tactics. Meanwhile as long as nations possess nuclear weapons the possibility of other, unforeseen conflicts careening out of control always exists. President Obama has declared a goal of abolishing nuclear weapons but perceivable progress toward this goal is lacking.

Whatever the consequences may be of greenhouse-induced climate change, they will be trivial compared to this prospect. There is no more urgent challenge facing humanity. None. This is it. For so long as nuclear weapons exist, they will be the only thing that matters.