Climate Change 2001:
Working Group I: The Scientific Basis
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11.6 Reducing the Uncertainties in Future Estimates of Sea Level Change

It is valuable to note that the reduction in the uncertainty of estimation of the long-term ice sheet imbalance reported in Sections 11.3.1 and 11.4 came from indirect constraints and the synthesis of information of different types. Such syntheses offer promise for further progress.

11.6.1 Observations of Current Rates of Global-averaged and Regional Sea Level Change

Sections 11.3.2.1 and 11.4 reveal significant uncertainty in the analysis of 20th century sea level change. Also, we have little knowledge of the regional pattern of sea level change. Observational determination of such a pattern would be a powerful test of the coupled models required for projections of globally averaged and regional sea level rise. Requirements for reducing uncertainties include:

For assessment of possible changes to the severity of storm surges, analyses of historical storm surge data in conjunction with meteorological analyses are needed for the world's coastlines, including especially vulnerable regions.

11.6.2 Ocean Processes

Requirements for improved projections of ocean thermal expansion include:

 

11.6.3 Glaciers and Ice Caps

Requirements for improved projections of glacier contributions include (see also Haeberli et al., 1998):

11.6.4 Greenland and Antarctic Ice Sheets

11.6.5 Surface and Ground Water Storage

Surface and ground water storage changes are thought to be having a significant impact on sea level, but their contribution is very uncertain (Table 11.10, Figure 11.9), and could be either positive or negative. They may become more important in the future, as a result of changes related not only to climate, but also to societal decisions that are beyond the scope of this scientific assessment. There are several general issues in climate-related aspects:

11.6.6 Summary

Sea level change involves many components of the climate system and thus requires a broad range of research activities. A more detailed discussion of the requirements is given in the report of the recent IGBP/GAIM Workshop on sea level changes (Sahagian and Zerbini, 1999). We recognise that it is important to assign probabilities to projections, but this requires a more critical and quantitative assessment of model uncertainties than is possible at present.



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