We study the quantitative effects of a carbon tax in a dynamic, general equilibrium model with production heterogeneity and technology adoption. The vintage technology available to a firm determines its emission rate. Adopting newer technology is
subject to a non-convex adjustment cost that leads firms to have (S,s) policy functions for technology and capital adjustment. We show that firm heterogeneity in emission rates determines the aggregate effects of a carbon tax in the short- and long- run. GDP losses from a representative firm model are more than double those with heterogeneous emission rates. Short-run effects depend on the policy implementation.