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Rising sea levels and increased storminess are expected to accelerate the erosion of soft-cliff coastlines, threatening coastal infrastructure and livelihoods. To develop predictive models of future coastal change we need fundamentally to know how rapidly coasts have been eroding in the past, and to understand the driving mechanisms of coastal change. Direct observations of cliff retreat rarely extend beyond 150 y, during which humans have significantly modified the coastal system. Cliff retreat rates are unknown in prior centuries and millennia. In this study, we derived retreat rates of chalk cliffs on the south coast of Great Britain over millennial time scales by coupling high-precision cosmogenic radionuclide geochronology and rigorous numerical modeling. Measured 10Be concentrations on rocky coastal platforms were compared with simulations of coastal evolution using a Monte Carlo approach to determine the most likely history of cliff retreat. The 10Be concentrations are consistent with retreat rates of chalk cliffs that were relatively slow (2-6 cm·y-1) until a few hundred years ago. Historical observations reveal that retreat rates have subsequently accelerated by an order of magnitude (22-32 cm·y-1). We suggest that acceleration is the result of thinning of cliff-front beaches, exacerbated by regional storminess and anthropogenic modification of the coast. [ABSTRACT FROM AUTHOR]

This paper describes numerical experiments using a climate--storm surge simulation system for the coast of the United Kingdom, with a particular focus on the southern North Sea and the Thames estuary in southeastern England. Time series of surges simulated in the southern North Sea by a surge model driven by atmospheric data from a regional climate model and surges simulated by the same surge model driven by atmospheric data from a global climate model are compared. A strong correspondence is demonstrated, and a linear scaling factor relating them is derived. This factor varies slowly with location. Around the Thames estuary, extreme surges are compared in the same way, and the linear scaling factor for the extremes is found to be similar to that for the full time series. The authors therefore assert that in seeking significant trends in surge at this location using this model arrangement, the regional model downscaling stage could be avoided, if observations were used to establish a suitable scaling factor for each location. The influence of the tide--surge phase relationship is investigated, and extreme sea levels at the mouth of the River Thames from regional-model-driven simulations are compared to the extreme event of 1953. Although the simulated levels are slightly lower, they are found to be comparable given the observational uncertainty. The assumption that time-mean sea level changes can be added linearly to surge changes is investigated at this location for large changes in time-mean sea level. The authors find that the primary effect of such an increase is on the speed of propagation of tide and surge, supporting the case for a simple linear addition of mean and extreme sea level changes. [ABSTRACT FROM AUTHOR]