Global and regional exposure to large rises in sea-level: a sensitivity analysis

This report examines the implications of large rises in sea level, both over the 21st century and beyond. Using GIS methods, an exposure analysis assesses the land area, existing population and existing economic activity situated within 10-m of present sea levels – these areas are not threatened within the 21st century, but looking further into the future these areas may be threatened if deglaciation of Greenland and the West Antarctic Ice Sheet occurs. The results emphasise the high impact potential of any rise in sea level. Regionally, most threatened land is in North America and Central Asia, with much being relatively unpopulated Arctic coastlines. In terms of population, East and South Asia dominate due to the their large populated delta areas. In terms of economic activity, East Asia, Europe and North America dominate, although this distribution is most likely to change during the 21st century. Using the FUND model, an impact assessment is also conducted over the 21st century for rises in sea level of up to 2-m/century and a range of socio-economic scenarios. This considers impacts assuming economically-optimum protection responses, so the actual impacts are less than the GIS analysis would suggest, but investment in the protection is required. While the costs of sea-level rise increase due to greater damage and protection costs, an optimum response in a benefit-cost sense remains widespread protection of developed coastal areas, as identified in earlier analyses. The socio-economic scenarios are also important in terms of influencing these costs. In terms of the four components of costs considered here, protection seems to dominate, with substantial costs from wetland loss under some scenarios. The regional distribution of costs shows a few regions experience most of the costs, especially South Asia, South America, North America, Europe, East Asia and Central America. However, there are some important limitations which suggest that protection may not be as widespread as suggested in the FUND analysis. Nonetheless, this analysis suggests that protection is much more likely and rational than is widely assumed, even with a large rise in sea level. In conclusion, this analysis confirms the significant exposure that exists to sea-level rise, but stresses that human responses including protection are rational even under large changes. Assuming widespread protection, investment is diverted from other uses. Much research remains to refine our understanding of these important issues