Uncertainties Regarding Specifics of Impact

The dominant scientific view is that global warming is real, and that its cause is human activity. The conversion of this knowledge into policy analysis, on the other hand, is not a clear-cut process, as illustrated by the following three passages:

What we currently have some idea about is the relative vulnerability of various locations to changes in sea level, based on coastal elevation, population density, coastal agricultural production, and ability to defend against rising seas (e.g., the Netherlands is relatively less vulnerable despite its low elevation than, say, the Mekong Delta, which has a much larger population density, lower income, few existing defenses, and a large amount of Viet Nam's cereal production). Given this type of background, we can simply say who is more likely to be damaged, and assume that the higher the sea level the more damage there is to deal with (or not).8

There has not been a systematic study of the problem of when small island cultures collapse on the whole. It also appears that this will vary geographically The timing of sea level rise will vary geographically, regardless of how fast the average rate is. It is very possible that sea level contributed from polar ice sheets will occur in decade-long pulses with lulls in between. This could put the most vulnerable areas in danger suddenly and without warning. It could also overrun attempts to build protective structures for major coastal cities, where adaptation is underway but major public works projects are "surprised" by unanticipated rapid rise. Note that we do not know how sea level rise will vary geographically. The pattern of differences observed in the past is not thought to indicate how the pattern will be in the future Models disagree widely on the future pattern.9

The diversity of African climates, high rainfall variability, and a very sparse observational network make predictions of future climate change difficult at the subregional and local levels. Underlying exposure and vulnerability to climatic changes are well established. Sensitivity to climatic variations is established but incomplete. However, uncertainty over future conditions means that there is low confidence in projected costs of climate change.10

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