He did. By assuming that damage was proportional to the fraction of the economy that a given sector represents. Which is an ok representation at very small amounts of warming. But when temperatures rise, the fact that the agriculture sector was, say, 3% of the economy, doesn’t mean that damage is only 3% when the amount of food goes to zero.
Didn’t some economist joker get a Nobel prize for saying the climate disaster wouldn’t cause much economic harm?
He did. By assuming that damage was proportional to the fraction of the economy that a given sector represents. Which is an ok representation at very small amounts of warming. But when temperatures rise, the fact that the agriculture sector was, say, 3% of the economy, doesn’t mean that damage is only 3% when the amount of food goes to zero.