Volume 11, No. 1, 2000
More than half the world’s population now lives on or adjacent to the coast and in the coastal lowlands. The late Quaternary history and evolution of these lowlands has become more than an academic interest .
In order to plan for sustainable land use changes and developments in these areas a knowledge and understanding of coastal and sea-level changes and of storms during the Holocene has strategic importance.
It is gratifying to note that the IPCC now concludes that changes in future sea level will not occur uniformly around the globe. But it is difficult to reconcile this conclusion with their global mean sea-level curves for AD 1990 – 2100 and AD 1990 – 2500. The form of the predicted sea-level rise curves differs significantly from the form of many of the curves based on empirical data for the period since the LGM. No acknowledgement is made of periods of accelerated sea-level change particularly sea-level rise, during this deglacial hemi-cycle, associated with the catastrophic discharge of meltwater, nor of the operation of the geoid.
Changes in the rates of sea-level rise have been recorded from both this and earlier interglacials with rates exceeding 20mm yr-1 and in some cases as much as 75mm yr-1. These are orders greater than anything predicted by the IPCC for the next 500 years. Changes in ice volume and accompanying changes in ocean water volume will affect the shape of the geoid because of the redistribution of mass on and in the Earth. Additions and abstractions of water from the ocean basins will not result in movements of sea level of the same magnitude and direction everywhere. There should be no expectation that sea-level curves from the same or different ocean basins should be concurrent. Contemporary variations in geoid ‘topography’ at sites such as Barbados and the Huon Peninsula from where sea-level curves have been constructed for the period since the LGM range from –52 m to +73 m.
These issues have been debated in a recently published book: Smith,D.E., Raper, S., Zerbini, S., Anchez-Arcilla, A. and Nicholls, R. (eds.) 2000. Sea-level changes and Coastal Processes : implications for Europe. Barcelona.
The concept of geoidal migration since the LGM is controversial, but has been adopted and will be tested as one of the goals of the Commission on Sea-level Changes and Coastal Evolution during Intercongress Period XVI 1999 – 2003. The best area to investigate the evidence for geoidal migrations during the Holocene is the Indian Ocean where there is a geoidal low >100 m deep and the geoid contours intersect the Indian coast at right angles. An interdisciplinary, multinational group has been established with a base in the Bose Institute, Calcutta to investigate sea-level changes around the northern Indian Ocean supported by the Commission and the Indian Ocean Sub-Commission. Simultaneously, the President of the Commission, Professor Nils-Axel Mörner has inaugurated a research programme on the evidence for sea-level changes on the Maldives, which is close to the centre of the geoidal low. The outcome of the research initiatives will enable a conclusion to be reached about the likely impacts of the IPCC’s putative sea-level rise scenarios to AD2500.
Copy for Quaternary Perspectives Volume 11, number 2 must reach the Editor by 14 February 2000.
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Professor Michael Tooley School of Geography, Kingston University, |