As the NY Times has written here and as commented on generally by Opinio Juris here, several local and state governments are taking action to implement Kyoto protocol protections themselves.
As Opinio Juris notes, "Under recent Supreme Court precedent, the President can preempt state and local laws that he deems inconsistent with a clearly established national policy? President Bush relied on this authority, in part, when he invalidated (or tried to invalidate) Texas laws denying certain rights to foreign defendants on death row."
While I agree with Julian that there is real Supreme Court precedent for preemption of state and local laws that oppose clearly outlined foreign policy, I somewhat doubt such precedent would be active here. From my understanding of the situation, these localities are voluntarily implementing environmental controls that mirror Kyoto requirements. The implementation of these controls is not clearly a statement on foreign affairs or in contradiction to current foreign policy and as such can be justified independent of any foreign policy concerns. Let me comment on these two points separately.
Unlike the Massachusetts Burma laws which were designed as state sanctions against a foreign regime, the implementation of Kyoto controls are content neutral. On their face, they make no statement as to what is the foreign policy of the United States. As such, they are not impeding the federal government's ability to "speak with one voice" in foreign affairs. Further, the US government did not clearly create a foreign policy where environmental controls are contrary to US foreign policy, but rather a policy that the US government was unwilling to obligate itself to implement national controls.
If the Bush Administration wants to block state and local implementation of Kyoto protections, it is going to have to find something other than a foreign affairs power argument to do so and that's a whole 'nother blog entry.