When It Rains It Pours: Cascading Uncertainty Shocks

The effects of uncertainty shocks are superadditive. On the basis of local projections, we find that the combination of nearby positive shocks can be multiple times more powerful than the sum of their stand-alone effects. In a standard New Keynesian dynamic stochastic general equilibrium model, uncertainty shocks are proven to be superadditive only when the model is solved under fourth- (or higher-)order perturbation. The fourth-order solution unlocks the fourth derivative of marginal utility, “edginess,” which is key to generating stronger reactions to multiple risks and superadditivity. Intuitively, an agent already bearing one risk is less willing to bear another in the presence of edginess.