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As recent court decisions have exhibited, constitutional law remains in flux. Indeed, commentators disagree about the specific head of power that would undergird federal jurisdiction for carbon pricing. Some point to the federal taxation power. However, this power requires that a tax be for the “raising of monies” rather than a charge that is primarily for regulating particular activities. Since it is applied only in select provinces and its express purpose is to encourage GHG reductions, the backstop carbon price is not intended to raise federal revenues. Moreover, if the backstop is a tax, it could be offside because our constitution requires a high degree of parliamentary control over taxes, and the backstop legislation gives discretion for the minister to decide which provinces face a federal carbon price.

Others believe a constitutional basis for the backstop could be the federal criminal law power, which has supported previous federal environmental legislation — for example, limits on contaminants and renewable content in diesel fuels. However, this power requires a prohibition backed by a penalty. In contrast, carbon pricing is not truly a prohibition since it expressly allows emissions for a price. Affirming the federal backstop as “criminal” legislation would dramatically increase the scope of the federal criminal law power.

For the backstop to be constitutional, the federal government would likely need to establish the regulation of GHGs as a national concern under the peace, order and good government power. The Supreme Court’s previous holding that marine pollution was such a national concern may provide precedent for regulating GHGs: somewhat analogously, the impact of GHGs on climate change occur beyond any one province.