"January 2005." Includes bibliographical references.

Summary -- Background and introduction -- Scientific and economic sources of uncertainty -- Uncertainty affecting costs -- Uncertainty affecting benefits -- Problems in valuation -- Agriculture: data gaps remain -- Health: questions about valuing lives saved -- Human settlements and ecosystems: valuing damages to nonmarketed goods and services -- Catastrophic damages: expert opinions vary widely -- The usefulness of subjective estimates -- Problems in aggregation -- Problems in comparing present costs and future damages -- Problems in determining the appropriate level of risk reduction -- Problems in aggregating costs and benefits across regions -- Policy implications -- Research and Development -- Mitigation -- Adaption.