Arizona recently joined the list of states that are preempting federal regulations in an effort to address climate change. Last week, Arizona’s governor, Janet Napolitano signed an executive order that will require the state to reduce greenhouse gas emissions to 2000 levels by 2020 and 50% below that by 2040. In addition, Napolitano created a new panel that will develop and implement the state’s climate strategy. Early indications suggest that Arizona will focus on reducing greenhouse gas emissions associated with transportation. The state will become the12th to adopt California’s Clean Car program, which requires a 30% reduction in greenhouse gas emissions for all new cars by 2011. Contrary to those who argue that such a plan would damage Arizona’s economy, the state estimates that the governor’s plan will save $5.5 billion by 2020. Unfortunately, the implementation of any emissions reduction strategy will require the consent of the Arizona state legislature, which has historically opposed efforts to address climate change.