Regional disparities would be small, according to most studies in recent years. “We … find that the regional variation is at best modest,” wrote economists Kevin A. Hassett, Aparna Mathur and Gilbert E. Metcalf in “The Incidence of a U.S. Carbon Tax: A Lifetime and Regional Analysis,” a January  2008 working paper by the American Enterprise Institute (AEI). They concluded that “variation across regions is sufficiently small that one could argue that a carbon tax is distributionally neutral across regions.”