Understanding and Adapting to Sea-Level Rise

Abstract

The surface of the ocean is never still. In most parts of the world, every few seconds the wind whips up waves. Then there are the daily changes experienced as tides. There are seasonal oscillations, and there are inter-annual changes which are sometimes manifested as decadal-to-century-scale periods of overall sea-level rise or fall. Then there are long-term sea-level changes, changes that are often hidden over timescales like that of a human lifespan by shorter-term changes. When we peer deep into the earth's past history, we cannot see such shorter-term changes clearly. Instead we see evidence only for the longer-term changes; evidence which includes often spectacularly elevated or sunken shorelines. During the Renaissance in Europe, philosophers were divided among those who thought that the presence of seashells high in the Alps was evidence of the Deluge described in the Christian Bible, and those who considered this idea fatuous and regarded such shells as having probably fallen from the hats of pilgrims. Both in their way were wrong. For centuries the subject of sea-level change was one that evaded the public interest, considered exclusively a topic for academics or fisherfolk, or of interest to those engaged in petroleum exploration or mariculture, for example, but hardly front-page news. All this changed in the 1970s and 1980s, as the spectre of future sea level rise first cast its long shadow over human futures. The world, it seemed, faced an unprecedented catastrophe as water levels around all of its coasts were apparently set to rise because of the rapid industrialisation during the past 150 years or so. When newspapers in the Cook Islands splashed headlines in the late 1980s talking of 10 m of sea-level rise in the next 10 years, people there were understandably alarmed. Such misinformation was fuelled by the many uncertainties involved in 'predicting' the rate and magnitude of future sea-level rise; early authoritative opinions talked of 3.5 m of sea-level rise by 2100, and many of the first impact studies were based on this figure. Since the establishment in 1988 of the Intergovernmental Panel on Climate Change (IPCC), 'estimates' of twenty-first-century sea-level rise have been revised downwards, yet we may still be faced with a 1.9 m sea-level rise by 2100 - and probably more thereafter.