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The 2008 A&WMA Critical Review, which was entitled

“Prospects for Future Climate Change and the Reasons for

Early Action,”1 focused on the vital issue of global climate

change. During the presentation of the review on June 25,

2008, in Portland, OR, Dr. Michael C. MacCracken, chief

scientist for climate change programs at the Climate Institute

in Washington, DC, gave an overview of the basic

science and history of the science behind climate change,

and presented a strong case for why urgent and early

action is needed to reduce ongoing changes in global

climate. He summarized the adverse impacts on human

systems and the environment that are occurring and are

projected for the future, and described the extent of emissions

reductions needed to prevent catastrophic impacts.

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.