After MacCracken’s presentation, a panel of four invited discussants was asked to contribute additional material relevant to the review. The discussants were told that this material could either dispute or reinforce and augment the original review. The discussion presented here by each panelist is self-contained, and joint authorship of this article does not imply that a discussant subscribes to the opinions expressed by others. In addition, a discussant’s commentary does not necessarily reflect the position of his or her respective organization.
The topic of the 2008 A&WMA Critical Review is very different from any other critical review undertaken by the Journal of Air & Waste Management in several ways. The primary way this topic differs is in the extent to which it has received broad and comprehensive scientific attention. The science, impacts, economics, mitigation of, and adaptation to climate change have been extensively studied over the last 30 yr. The Intergovernmental Panel on Climate Change (IPCC), established by world governments in 1988, has completed four comprehensive assessments and many additional reports on climate change. The assessments were all written and peerreviewed by thousands of scientists worldwide with expertise in the fields that contribute to climate change science. Where there is not yet full agreement, the IPCC findings were expressed as a range, and where possible, the degrees of likelihood and confidence in the results were expressed. For example, because we cannot know precisely what future technologies and emissions will be, the IPCC considered the potential consequences for a family of emissions scenarios representing very different global futures.
The IPCC assessments, and particularly their supporting chapters, are the most authoritative and complete reviews of the scientific literature on climate change. Mac-Cracken notes in the critical review1 that “these assessments represent the international scientific consensus on climate change, its impacts, and the possibilities for responding.
Taken as a whole, the IPCC’s work provides a comprehensive baseline of information for consideration by governments and the public.”