This paper analyzes the effects of nonatmospheric consumption externalities on optimal commodity taxation and on the social cost and optimal levels of public good provision. A negative consumption externality, by lowering the social cost of public good provision, may require the second‐best level of public good provision to exceed the first‐best level. If those households who are most important for building up the consumption reference level respond the least to commodity taxation, the second‐best commodity tax rate may fall short of the first‐best rate. Moreover, in this case, heterogeneity may imply an equity‐efficiency tradeoff. This tradeoff is present only if the consumption externality is of the nonatmospheric type.