Sea-level rise and coastal change: the past as a guide to the future
There is a broader awareness than ever that we live in a changing environment. The spectre of climate change is of wide concern, and the observed trends and anticipated consequences of an acceleration of sea-level rise pose a series of threats for the future of people who live in coastal communities. Coastal geoscientists are able to reconstruct the position of former sea levels; they can also explain much of the geographical variation in relative sea-level history. Successive collaborative projects (many under the auspices of international programmes sponsored by IGCP and INQUA) derived local sea-level histories and compiled atlases of relative sea-level curves, and some addressed past coastal behaviour in response to these changes. The most recent International Geological Correlation programme project 588, 'Preparing for coastal change', continues this impressive lineage of projects that have laid the foundations for our understanding of sea-level behaviour over the late Quaternary. Today, these issues are a major focus in the debate about climate change, its impacts, and the need for adaptation on the most vulnerable shorelines. There is clearly a role for the palaeoenvironmental skillset honed through successive geoscientific projects. Investigations of past coastal environments have provided the tools for delineating past levels of the sea, but the stratigraphical and geochronological studies which were necessary to reconstruct the sea-level position also provide insights into where the shoreline lay and how the coast behaved as sea level changed. If the present is the key to the past, then the past, seen from the context of the present, can be a guide to the future. Collaborative projects and international co-operation between scientists from different disciplines can play important roles in future debates about how our world will change. First, the lessons learnt about the patterns of variation of relative sea level need to be more widely recognised by climate scientists. Efforts aimed at establishing the rate of future global sea-level rise need to be complemented by protocols to determine regional deviations from that mean rate of sea-level change. Second, modes of coastal change need to be identified to replace simplistic heuristics of coastal response, such as the Bruun rule. Simulation modelling offers a suite of tools that appear to give coastal managers guidance, but geoscientists should strive to produce evidence that can be used to develop and validate model behaviour. Coastal scientists presently have a relatively good understanding of coastal behaviour at millennial timescales, and process operation at contemporary timescales. However, there is less certainty about how coasts change on decadal to century timescales. It is these latter timescales which are particularly important for managers and policy-makers. These, and related challenges, provide a focus for research that will have a relevance for society that the coastal geoscience research community has rarely experienced.
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