North Korea: Why War Is the Only Option Now
Examining nuclear war near misses using engineering reliability assessment methods, Barrett, Baum, and Hostetler estimate that there was a 2% chance per year of an accidental U.S.-Soviet nuclear war during the Cold War. Since President Kennedy's estimate of the probability of nuclear war arising from the Cuban Missile Crisis alone puts the probability of accidental nuclear war at between 1.4% and 2.4% per year over the course of the Cold War (1960 to 1989) without even considering the Petrov incident, the NORAD training tape incident, and other such incidents, this 2% per year probability seems very plausible.
Does this Cold War estimate apply to North Korea? Examining the factors that contribute to the probability of accidental nuclear war, I think that the probability of accidental nuclear war with North Korea is if anything higher (and probably much higher) than was the probability of an accidental U.S.-Soviet nuclear war.
To err in favor of the deterrence option, then, I estimate the cost of gambling on deterrence under two cases. In the first, I assume that the probability of an accidental U.S.-North Korean nuclear war is 2% per year. In the second I assume that there is one incident over the next 30 years that creates a 25% chance of an accidental nuclear war.
Should the U.S. Take the Deterrence Gamble or Launch a Preventive War?
If the U.S. chooses to deal with the North Korean nuclear threat by means of a preventive war, then there is a 100% chance of a war in 2018 (clearly, if the U.S. is going to launch a preventive war, then the sooner the better). This war will lead to North Korea launching 25 nuclear weapons (20 kt each) at cities in South Korea and Japan and will lead to 1.4 million deaths (given the assumptions above).
I note that this is an extremely pessimistic estimate. A preventive war will almost certainly begin with a U.S. nuclear strike on North Korean command-and-control and nuclear assets with the goal of eliminating North Korea's ability to launch a nuclear attack. Furthermore, the U.S. will utilize its missile defense assets to defend South Korea and Japan against any North Korean attack. However, to err in favor of the deterrence option, I assume here that this U.S. strike has no effect on the probability that North Korea can detonate a nuclear weapon on target. While it would certainly be rash to assume that the U.S. efforts to eliminate North Korea's nuclear threat will be 100% effective, it is highly likely that the U.S. will be able to degrade the effectiveness of North Korea's nuclear threat to some degree.
If the U.S. chooses to gamble on deterrence, then the probability of accidental nuclear war will lead to 1) 7.5 million deaths on average in the 2% chance of accidental nuclear war per year case; or 2) 4.4 million deaths on average in the single 25% chance of accidental nuclear war case.
This estimate of deaths under the deterrence gamble is extremely optimistic. First, I assume that the probability of a successful detonation remains constant over time. However, it is highly likely that North Korea's ability to successfully detonate a nuclear weapon on target in the U.S. will increase over time as North Korea continues its rapid advance in weapon and missile design. Second, I assume that North Korea's ability to increase weapon yield stops at 250 kt. Instead, it is highly likely that North Korea will eventually be able to develop full hydrogen bombs and so increase the yield of their weapons to far higher levels. It follows that an accidental war in the future will be far more devastating than I have assumed and may be sufficiently severe so as to pose an existential threat to the U.S.
On the other hand, I am also assuming that advances in missile defense do not eliminate the North Korean nuclear threat. While I strongly support a much stronger effort to improve U.S. missile defense capabilities, caution advises against assuming that missile defense will be completely effective (and certainly those making the case for gambling on deterrence are not doing so because they think that missile defense will work). But, to the extent that one is willing to bet on missile defense, the case for deterrence is strengthened.
So, the bottom line of this analysis is that gambling on deterrence is far more dangerous than launching a preventive war now.