Explain how IAMs differ from climate models
Explain why the IAMs differ from each other, and why it is important to use more than one
Explain why Radiative Forcing is an important concept.
The “Historical Overview” section is useful and well-written. The overview of the IPCC reports (beginning at line 414) could benefit from a very brief statement of what the IPCC is as well as the scope of IPCC assessments (i.e., review of current literature; there is a common misconception that IPCC performs research). At lines 434-441 it could be noted that the models are moving toward finer resolution that can include some topographic features that are important to U.S. climate. Finer resolution in the ocean now allows some important atmosphere-ocean coupling processes such as ENSO to be represented in some AOGCMs (see e.g., van Oldenborgh et al. 2005; Wittenberg et al. 2006).
The three AOGCMs and modeling groups should be briefly introduced in this chapter. Care should be taken to distinguish the AOGCMs from the IAMs, especially for the benefit of non-specialists. Text (perhaps a box) describing these types of models and functions as an introduction to a non-technical reader should be included.
An indication should also be given as to whether the AOGCMs used in the study are appropriate to the task at hand. This need not be a detailed performance evaluation; it would be adequate simply to state that intercomparison studies have shown that the performance of these models is comparable to other state of the art climate models.
Finally, the methodology and its limitations should be made clearer at the outset and should also explain why new emissions scenarios are needed. . .
L428-429: “model” should be plural, “models”
L506: Methane is reactive not only in the troposphere but also in the stratosphere (being a main source of water vapor in the upper stratosphere).
The committee feels that the chapter contains much useful material that serves to fulfill the mandates of the prospectus. It also feels that the chapter can be improved in several regards.