Nuclear Winter with Alan Robock and Brian Toon

The UN voted last week to begin negotiations on a global nuclear weapons ban, but for now, nuclear weapons still jeopardize the existence of almost all people on earth.

I recently sat down with Meteorologist Alan Robock from Rutgers University and physicist Brian Toon from the University of Colorado to discuss what is potentially the most devastating consequence of nuclear war: nuclear winter.

Toon and Robock have studied and modeled nuclear winter off and on for over 30 years, and they joined forces ten years ago to use newer climate models to look at the climate effects of a small nuclear war.

The following interview has been heavily edited, but you can listen to it in its entirety here or read the complete transcript here.

Ariel: How is it that you two started working together?

Toon: This was initiated by a reporter. At the time, Pakistan and India were having a conflict over Kashmir and threatening each other with nuclear weapons. A reporter wanted to know what effect this might have on the rest of the planet. I calculated the amount of smoke and found, “Wow that was a lot of smoke!”

Alan had a great volcano model, so at the American Geophysical Union meeting that year, I tried to convince him to work on this problem. Alan was pretty skeptical.

Robock: I don’t remember being skeptical. I remember being very interested. I said, “How much smoke would there be?” Brian told me 5,000,000 tons of smoke, and I said, “That sounds like a lot!”

We put it into a NASA climate model and found it would be the largest climate change in recorded human history. The basic physics is very simple. If you block out the Sun, it gets cold and dark at the Earth’s surface.

We hypothesized that if each country used half of their nuclear arsenal, that would be 50 weapons on each side. We assumed the simplest bomb, which is the size dropped on Hiroshima and Nagasaki — a 15 kiloton bomb.

The answer is the global average temperature would go down by about 1.5 degrees Celsius. In the middle of continents, temperature drops would be larger and last for a decade or more.

We took models that calculate agricultural productivity and calculated how wheat, corn, soybeans, and rice production would change. In the 5 years after this war, using less than 1% of the global arsenal on the other side of the world, global food production would go down by 20-40 percent for 5 years, and for the next 5 years, 10-20 percent.

Ariel: Could you address criticisms of whether or not the smoke would loft that high or spread globally?

Toon: The only people that have been critical are Alan and I. The Departments of Energy and Defense, which should be investigating this problem, have done absolutely nothing. No one has done studies of fire propagation in big cities — no fire department is going to go put out a nuclear fire.

As far as the rising smoke, we’ve had people investigate that and they all find the same things: it goes into the upper atmosphere and then self-lofts. But, these should be investigated by a range of scientists with a range of experiences.

Robock: What are the properties of the smoke? We assume it would be small, single, black particles. That needs to be investigated. What would happen to the particles as they sit in the stratosphere? Would they react with other particles? Would they degrade? Would they grow? There are additional questions and unknowns.

Toon: Alan made lists of the important issues. And we have gone to every agency that we can think of, and said, “Don’t you think someone should study this?” Basically, everyone we tried so far has said, “Well, that’s not my job.”

Ariel: Do you think there’s a chance then that as we acquired more information that even smaller nuclear wars could pose similar risks? Or is 100 nuclear weapons the minimum?

Robock: First, it’s hard to imagine how once a nuclear war starts, it could be limited. Communications are destroyed, people panic — how would people even be able to rationally have a nuclear war and stop?

Second, we don’t know. When you get down to small numbers, it depends on what city, what time of year, the weather that day. And we don’t want to emphasize India and Pakistan – any two nuclear countries could do this.

Toon: The most common thing that happens when we give a talk is someone will stand up and say, “Oh, but a war would only involve one nuclear weapon.” But the only nuclear war we’ve had, the nuclear power, the United States, used every weapon that it had on civilian targets.

If you have 1000 weapons and you’re afraid your adversary is going to attack you with their 1000 weapons, you’re not likely to just bomb them with one weapon.

Robock: Let me make one other point. If the United States attacked Russia on a first strike and Russia did nothing, the climate change resulting from that could kill almost everybody in the United States. We’d all starve to death because of the climate response. People used to think of this as mutually assured destruction, but really it’s being a suicide bomber: it’s self-assured destruction.
Ariel: What scares you most regarding nuclear weapons?

Toon: Politicians’ ignorance of the implications of using nuclear weapons. Russia sees our advances to keep Eastern European countries free — they see that as an attempt to move military forces near Russia where [NATO] could quickly attack them. There’s a lack of communication, a lack of understanding of [the] threat and how people see different things in different ways. So Russians feel threatened when we don’t even mean to threaten them.

Robock: What scares me is an accident. There have been a number of cases where we came very close to having nuclear war. Crazy people or mistakes could result in a nuclear war. Some teenaged hacker could get into the systems. We’ve been lucky to have gone 71 years without a second nuclear war. The only way to prevent it is to get rid of the nuclear weapons.

Toon: We have all these countries with 100 weapons. All those countries can attack anybody on the Earth and destroy most of the country. This is ridiculous, to develop a world where everybody can destroy anybody else on the planet. That’s what we’re moving toward.

Ariel: Is there anything else you think the public needs to understand about nuclear weapons or nuclear winter?

Robock: I would think about all of the countries that don’t have nuclear weapons. How did they make that decision? What can we learn from them?

The world agreed to a ban on chemical weapons, biological weapons, cluster munitions, land mines — but there’s no ban on the worst weapon of mass destruction, nuclear weapons. The UN General Assembly voted next year to negotiate a treaty to ban nuclear weapons, which will be a first step towards reducing the arsenals and disarmament. But people have to get involved and demand it.

Toon: We’re not paying enough attention to nuclear weapons. The United States has invested hundreds of billions of dollars in building better nuclear weapons that we’re never going to use. Why don’t we invest that in schools or in public health or in infrastructure? Why invest it in worthless things we can’t use?