In 1985, Bird reported on a project undertaken by the International Geographical Union’s Commission on the Coastal Environment: this found 70 per cent of the world’s sandy coastline undergoing net erosion. As 60 per cent of the global population (or nearly 3 billion people) live in the planet’s coastal zones, and two-thirds of the world’s cities with populations of 2.5 million or more are located in open coast or estuarine locations (Viles and Spencer 1995), Bird’s (1985) statistic identifies a major environmental issue. It is an issue already strongly imprinted on many local, and national, consciences. Strong conflicts can arise in the tackling of coastal erosion between local residents; local, regional and national regulatory bodies and interest groups; and consultant scientists: the interaction of physical processes and economic, social and political forces makes coastal erosion a strongly geographical problem. Furthermore, any coastal study must take account of the great diversity of coastal settings and of the role of environmental change over the last 10,000 years in determining contemporary shoreline morphology (see Box 8.1). There has been a growing concern in the last decade that coastlines are at risk and under pressure. Two broad sets of processes, both potentially accelerating, have been identified.
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,