UPDATE 2/24/12: Commenter Chew Bird notes that some scientists commenting at The Atlantic and Wellestein's own blog strongly disagree with him. They argue that a nuclear detonation is a reasonable measurement of energy output.
Last week, a meteor exploded over Russia with, according to some press descriptions "the force of 30 Hiroshima bombs." These were references to the US atomic bombing of Hiroshima, Japan on 6 August 1945. Atomic historian Alex Wellerstein says that the analogy makes little sense:
"In general," he added, "What I don't like is ... the idea that kiloton or a megaton is just an energy unit, that it's equivalent to so many joules or something. Because you could do that. You could claim that your house runs so many tons of TNT worth of electricity per year, but it sort of trivializes the notion." [...]
But nuclear weapons deliver more than just sheer force; there's also incredible heat, orders of magnitude hotter than a meteor's explosion, (most of the people who died at Hiroshima and Nagasaki, Wellerstein says, died of fire), and, of course, the radiation. The radiation brings sickness, makes land uninhabitable in the long term, and can have residual genetic effects that long outlast the bomb's immediate destruction. "It's sort of the sum of these effects that we think of when we think of what's the problem with nuclear weapons," he says. To only think of an atomic weapon in terms of the kilotons of energy released glosses over the totality of the terror these bombs bring.
It's one thing to use an atomic explosion as a unit for describing a meteor's explosion -- the two are similar in that much of their energy is released as a blast wave -- but the comparison is even worse when applied to other sorts of disasters, Wellerstein contends. "My least favorite is when this sort of thing is applied to literally non-explosive phenomena: tsunamis, earthquakes, tornadoes. These are sometimes talked about in terms of their energy release. And you can always quantify an energy release -- you can just do the conversion to nuclear units and say, 'Oh my God look how much energy this is!' But, you know: An earthquake is a very different release of energy; a tsunami is a very different release of energy. The effects are just not comparable. They're nothing like nuclear weapons."