This paper examines the effects of international trade in a model with global pollution that accumulates over time because of production emissions in each country. If countries cooperatively determine their environmental policies, autarky and free trade in the absence of trade costs generate the same optimal solution. By contrast, if environmental policies are determined noncooperatively, the effects of trade on global pollution and welfare are ambiguous because policy games can result in multiple equilibria. Although trade increases both the lower and upper bounds of the pollution stock, whether trade expands the range of possible steady-state pollution levels is ambiguous. The analysis then extends to consider trade costs. Copyright � 2010 Blackwell Publishing Ltd.