The principles of “common but differentiated responsibility” (CBDR) and sustainable development play an integral role in international environmental law. However, these principles have come under fire in recent years, particularly from the global North, which has grown impatient over the lack of contribution on climate change from the emerging economies. Much effort has been expended toward the establishment of greater contribution, and the shouldering of greater responsibility from these countries.

In 1990, when the Clean Air Act (CAA) was last substantially amended, atmospheric carbon dioxide levels stood at about 350 parts per million (ppm). Now they are close to 414 ppm, and the U.S.