eight reviewers increased the upper estimates of thermal expansion for a given level of atmospheric forcing by about 15 percent. Of the remaining reviewers, the Balling and Wigley & Raper assumptions both implied substantially lower 1%-high estimates. All of Balling’s estimates had low sensitivi...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.391.6035 http://papers.risingsea.net/federal_reports/probability-chapter_3b.pdf |
| Summary: | eight reviewers increased the upper estimates of thermal expansion for a given level of atmospheric forcing by about 15 percent. Of the remaining reviewers, the Balling and Wigley & Raper assumptions both implied substantially lower 1%-high estimates. All of Balling’s estimates had low sensitivities, and because of their narrower range for ∆T 2X Wigley & Raper also had a downward impact. But these moderating assumptions had a small impact on the high end of the range for the overall assessment, for two reasons. First, these comments removed only about 10 percent of the high-temperature simulations. Second, the mathematics of, for example, a normal distribution are such that even if half of the reviewers eliminated all of their high-scenario estimates, the overall 1%-high estimates would rise if the other half of the reviewers increased σ by 15 percent. Perhaps most important, the reviewers expanded the high end of the uncertainty range regarding the polar temperature estimates that the Greenland and Antarctic models use in Chapters 4 and 5. Three of the reviewers substantially increased the high estimates of Greenland temperature sensitivity, outweighing any downward impact on the high end from the revisions suggested by Manabe and MacCracken; the low end of the range was also broadened. Similarly, half of the reviewers suggested that eventually, the Antarctic circumpolar ocean is likely to warm as much as the Earth’s average temperature warms, with three of the reviewers suggesting that the polar water could warm twice as much. Even assuming a lag on the order of one hundred years, such a sensitivity suggests that the Antarctic ocean could warm by 6 to 8˚C in the next two centuries. By comparison, studies of the potential sensitivity of Antarctica have assumed only a 1˚C circumpolar ocean warming (see Chapter 6). If, as the reviewers suggest, there is a significant risk that circumpolar ocean temperatures could warm 4 to 8˚C, recent assessments of the vulnerability of Antarctica may have overlooked the ... |
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