Carbon abatement policies in large open economies affect both the allocation of domestic resources and international market prices. A change in international prices implies an indirect secondary burden or benefit for all trading countries. Based on simulations with a large-scale computable general equilibrium model of global trade and energy use, we show that international spillovers have important welfare implications for carbon abatement policies designed to meet exogenous emission reduction targets. We present a decomposition of the total welfare effect of carbon abatement policies into a primary domestic market effect (at constant international prices) and a secondary international spillover impact as a result of changes in international prices. This decomposition reveals the extent to which domestic abatement costs are increased or decreased as a result of the impact of carbon abatement on international prices.