Executive Summary

The Executive Summary is more balanced in tone than the Abstract; however, the committee notes several instances where statements in the Executive Summary are not well-supported in the four chapters. The committee does not necessarily disagree with these statements, but only recommends that the authors ensure they are supported if they are included in the Executive Summary. In particular, and in keeping with Major Comments 4 and 5, claims of trends (increases or decreases), which are listed at length, should be rooted consistently in statistical significance and the underlying uncertainties summarized.

The Executive Summary contains several sections with seemingly random, single-sentence paragraphs that should be consolidated, when possible, into coherent themes. Section 6 should be revised to concisely and adequately reflect the recommendations provided in Chapter 4 (see Major Comment 10).

Specific Suggestions:

  • Lines 26-29: This paragraph is vague and may be interpreted as alarmist; it should focus on some specific extremes that definitely appear to be changing (e.g., maximum temperatures and precipitation intensity). At a minimum, the committee suggests inserting “some” before “extremes” on line 26.

  • Line 66: This sentence on problems of climate models simulating extremes is correct, but it is not obviously related to the previous two sentences, which describe that changes in climate averages imply changes in the tails of the distribution and hence in climate extremes. Perhaps a more direct connection could be made or the sentence put in a separate paragraph where the difficulties for models in simulating extremes are elaborated a little, including both resolution and process limitations.

  • Line 87: What is the conclusion of this paragraph?

  • Line 113: What does “are likely to be attributable to” mean? Does it mean that they have been attributed to, or does it mean they would be attributed to, but the relevant studies haven’t been done yet? There are no formal attribution studies that attribute the global changes in these phenomena to anthropogenic forcing. There is a single attribution study on these by Christidis et al. (2005) but it only considers limited global coverage, as there are no data in many regions.

  • Line 118: In this case there are a number of studies that have detected and attributed observed changes in Sea Surface Temperature (SST) to increasing greenhouse gases. Does this statement refer to global average SST or regional SST in the tropics?

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