Can a nuclear winter stop global warming?

Expert dispute: do atomic bombs ruin the world's climate?

That is entirely plausible. This year's huge forest fires in Russia, Alaska and Brazil injected little soot into the stratosphere, although the area burned was probably larger than the entire German forest. A large fire is not enough to drive the soot up to a height of ten or more kilometers. Only a firestorm can do that. Such a phenomenon creates a chimney effect because the hot combustion gases escape upwards, while air rushes in from all sides and continues to ignite the fire.

A firestorm only occurs if the area is at least 1.3 square kilometers, there is more than 40 kilograms of combustible material per square meter and more than half of it is burning at the same time. However, these figures are only approximations and come from the experiences of the Second World War, when the Allied area bombings in Germany repeatedly triggered firestorms in German cities. The atomic bomb explosion over Hiroshima created a devastating firestorm with a delay of 20 minutes. The second attack on Nagasaki broke out numerous fires, but they did not flow together in a firestorm.

Firestorm - yes or no?

Jon Reisner's working group came to the conclusion that when designing today's cities in India and Pakistan, firestorms are hardly to be expected - and thus also not a global nuclear winter. That didn’t let Alan Robock’s working group rest. Four of the six authors of the 2007 study, together with other scientists, published another paper on October 2, 2019, in which they reaffirmed their conclusions.

This time they assume an even more brutal confrontation. Instead of calculating the effects of 100 atomic bombs, each with 15 kilotons of explosive force, they developed three scenarios that are somewhat more complex. Basically, it boils down to Pakistan detonating 150 atomic bombs and India 100 atomic bombs over the opposing population centers, each with 15, 50 or 100 kilotons of explosive force. There are also minor explosions over military bases.

Between 50 and 125 million people would be directly victims of the war. And because the authors still assume that a large part of the black carbon produced will rise quickly into the stratosphere, global temperatures would drop by between two and five degrees. Precipitation would decrease by 15 to 30 percent, and the climate would take more than ten years to recover. The danger of bad harvests and global famine is correspondingly great.

However, as in the work from 2007, the authors fail to sufficiently substantiate their assumptions about the pollution of the stratosphere with soot. They argue in a relatively detailed manner, but they do not have their own simulation of the course of the fire to offer. So they cannot score on the central theme of the controversy.