Coastline changes: A reconsideration of the prevalence of recession on sandy shorelines.

It is often inferred that rising sea levels will result in widespread coastal recession. Erosion appeared prevalent in a worldwide compilation of evidence derived from maps and aerial photographs undertaken in the 1980s by the Commission on the Coastal Environment. Eric Bird, chair of the commission, inferred that >70% of sandy coastlines had retreated, a generalisation that has been widely cited. We reconsider these findings in respect of subsequent advances in shoreline mapping, including greater precision possible using geographical information systems and more frequent remote sensing imagery with increased spatial, spectral and temporal resolution. Satellite-derived shorelines now enable broad global and regional generalisations about shoreline position. Beaches fluctuate over a range of timescales, meaning that trends in their position are highly dependent on techniques and temporal scales adopted for monitoring. Recent global- and regional-scale shoreline assessments indicate that many sandy shorelines have been stable, and that detectable retreat has occurred on fewer beaches than previously inferred. Accretion is apparent on some coasts, particularly where engineering interventions protect or have reclaimed land. There is considerable variability in the behaviour of monitored beaches, and it is not yet possible to decipher a response to the gradual centimetre-scale rise in sea level of recent decades. Instead, we re-emphasise the several other factors that were considered to contribute to recession by the Commission, many of which relate to a change in sediment budget. To provide insights into future coastline behaviour, a better understanding of the multiple drivers on individual beaches is needed to discriminate between erosional events and longer-term trends in shoreline position.