With its antique Chevrolets and outdated politics, the communist island of Cuba seems like a time capsule of 1950s. So is it any surprise that Fidel Castro is worried about nuclear winter , a notion popularized by astronomer Carl Sagan 25 years ago ?
The island’s strong man has recently been fretting over the possibility of a nuclear exchange involving the United States and either North Korea or Iran — the subject of his first speech to the Cuban parliament in 4 years earlier this month. On Monday, Castro called together four top scientific advisers including Tomás Gutiérrez Pérez, head of Cuba’s meteorology service, and science minister Col. José Luis Navarro Herrero, to brief him on the consequences of a small-scale nuclear war.
Today, Cuba’s communist newspaper Granma published an essay by Castro entitled “The Nuclear Winter” (read it in English  or in Spanish ), in which the retired leader expressed his surprise at what he learned:
I feel embarrassed to be unaware of the subject, one that I have not even heard mentioned before. On the contrary, I would have understood much earlier that the risks of a nuclear war were far more serious than I imagined.
I assumed that the planet would be able to withstand the explosion of hundreds of nuclear bombs calculating that, in both the United States and the USSR, countless tests have been carried out over the years. I had not taken into account a very simple reality: it is not the same thing to explode 500 nuclear bombs over 1,000 days as it is to do the same thing in one day.
I was able to learn more about it when I requested information from several experts on the subject. One can imagine my surprise when I learned that we do not need a nuclear world war for our species to perish.
A nuclear conflict between the two weakest nuclear powers would be sufficient, such as India and Pakistan – who nevertheless possess far more than 100 weapons of this kind – and the human race would disappear.
Although fears over nuclear winter have generally faded along with the Cold War, some recent research suggests even a limited conflict could pollute the atmosphere enough to cause worldwide famines.
Castro’s letter relies heavily on the research of Owen Brian Toon, an atmospheric physicist in the Department of Atmospheric and Oceanic Sciences at the University of Colorado, Boulder. Toon, who collaborated with Sagan on the original nuclear winter theories, has recently been ringing alarm bells about the dangers of more limited regional conflicts. Toon reported in Science  in 2007 that even a “small-scale” conflict involving 100 weapons could kill 21 million people and release enough smoke to cause “substantial global-scale climate anomalies” lasting years. He renewed the warning this year in a Scientific American article  saying a conflict involving just 0.4% of the world’s 25,000 nukes would produce enough smoke to cripple global agriculture.
Although Castro doesn’t mention Toon, his letter quotes heavily from the Scientific American article, including the scientist’s conclusion that “the only way to eliminate the possibility of climatic catastrophe is to eliminate the weapons.”
UPDATE 4 P.M.: Brian Toon e-mails to say: "Yes he appears to be referencing our work. I don't know anything else about what he is thinking. At least one world leader has taken the time to inform themselves about the consequences of nuclear conflicts involving small numbers of weapons."