At no point in this nation’s history has climate change been a more hotly and publicly debated topic than it is today. Although it may be said that most Americans accept the scientific evidence that climate change poses a serious threat to human health, development and even existence, there is widespread disagreement about how the threat should be addressed, and there is a vocal minority that asserts it does not even exist (or that its severity has been exaggerated).1

These debates are being played out in the public sphere and in the proceedings of all three branches of U.S. government, creating a frequently changing vision of an American future that may include a “low-carbon economy” vastly different from the economy we see today.

In 2007, pushed by certain state governments that had already grown concerned about climate change, the U.S. Supreme Court opened the door to federal regulatory action with its 5-4 ruling in Massachusetts v. EPA.2 In that decision, the court ruled that carbon dioxide and other greenhouse gases are, “without a doubt,” “air pollutants” within the meaning of the Clean Air Act and that (absent new legislation) the Environmental Protection Agency was required to regulate them as such.