IPCC Report.pdf - Adam Curry

Changes in Climate Extremes and their Impacts on the Natural Physical EnvironmentChapter 3external forcings affecting extremes include net increases in temperatureinduced by changes in radiation, enhanced moisture content of theatmosphere, and increased land-sea contrast in temperatures, which can,for example, affect circulation patterns and to some extent monsoons.At regional and local scales, additional processes can modulate theoverall changes in extremes, including regional feedbacks, in particularlinked to land-atmosphere interactions with, for example, soil moistureor snow (e.g., Section 3.1.4). This section briefly reviews the currentunderstanding of the causes (i.e., in the sense of attribution to eitherexternal forcing or internal climate variability) of large-scale (and someregional) changes in the mean climate that are of relevance to extremeevents, to the extent that they have been considered in detection andattribution studies.Regarding observed increases in global average annual mean surfacetemperatures in the second half of the 20th century, we base our analysison the following AR4 assessment (Hegerl et al., 2007): Most of theobserved increase in global average temperatures is very likely due tothe observed increase in anthropogenic greenhouse gas concentrations.Greenhouse gas forcing alone would likely have resulted in a greaterwarming than observed if there had not been an offsetting coolingeffect from aerosol and other forcings. It is extremely unlikely (