He breaks his concern down into two separate but related points: First off, he writes on his blog, the character of a nuclear blast is not really comparable to a non-nuclear explosion, even when the amounts of force delivered are similar. "It's just sort of a raw energy output with no attention to exactly how that energy is being delivered. And without attention to that, it doesn't really tell you what would happen other than that, yes, if a meteor hit your town directly it would flatten most of your town, and, yes, a nuclear weapon would also flatten most of your town."
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."
Wellerstein's second concern boils down to his doubts that these comparisons really serve the public in any way. What does it even mean to say that something is 30 times the size of Hiroshima? Do people have a really strong sense of even what one Hiroshima looks like, and can they then imagine an energy release 30 times that? "Heck, I barely have any point of reference and I'm constantly searching for them!" he wrote on his blog.
Obviously, reporters are just trying to convey that the meteor was huge. And Wellerstein says he gets that. "But I feel like you could do that without making people get the untrue sentiment that nuclear weapons are small. If even a very small nuclear weapon, if it went off in a modern city, would be an atrocious thing."