The first set concerns the impact of sea level rise over the next 100 years consequent upon human-induced global climate change. The figure of c. 100-150 cm of sea level change by AD 2100 is still widely found in the literature, but current 'best guess' estimates for this period are 49 cm, a considerable downward revision on earlier figures (see Warrick et al. 1996 for detailed discussion and French et al. 1995a for geomorphological and ecological implications). However several caveats should be applied to this apparently comforting reduction. First, very large uncertainties remain in the predictions of global environmental change. Second, it is not clear how the primary effect of sea level rise might influence a range of secondary effects, such as changing tropical cyclone magnitudes and frequencies and mid-latitude wave climates, which might in themselves have greater impact on coastal communities than sea level rise per se. Third, although the expected sea level rise for the next 100 years is now much lower than previously envisaged, it still represents a significant increase on the previous 100 years. The magnitude of expected sea level rise converts to an average rate of sea level rise of 4.5 mm a-1. Although it is difficult to provide a single figure for the rate of sea level rise over the last 100 years, Warrick et al. (1996) suggest an average rate of rise of 1.8 mm a-1. Thus future rates are currently expected to be 2.5 times those of the last 100 years.

Any future sea level change will be played out against the backdrop of the second set of major processes to affect the world's coastlines. This is the creation of highly modified, 'artificial' shorelines as a result of long-continued, but now larger-scale, human modification and utilisation of the coastal zone. Typically 30-40 per cent of open coasts in developed countries (e.g. USA, England, Japan) have protection against flooding, Coastal dynamics, including erosion, are controlled at the large scale by two sets of factors, one historical (in the broadest sense) and one contemporary. In the first, coastal type is controlled by plate tectonic setting, and this provides a broad emergence/submergence categorisation. This in turn is overlain by more immediate historical factors, particularly the nature of sea level change over the last 10,000 years of the postglacial transgression. Site-specific variations in sea level in this period have resulted from the varying contribution of regional isostatic (affecting the movement of land surfaces) and global eustatic (affecting the volume of the oceans) factors to sea level change. Thus the different sea level histories of, for example, Australia, where present sea level was reached 6000 years ago, and Arctic Canada, where sea levels have been falling since the start of the deglaciation, are a component in explaining shoreline morphology. This historical backdrop is then worked upon by current global variations in wave energy, tidal regime and, for vegetated coastal ecosystems, biogeographic patterns and processes. . .