SEA-LEVEL RISE AND PUBLIC DISCOURSE: THE NEED FOR BASIC GEOLOGIC PRINCIPLES

Constructive public discourse about sea level rise requires common understanding of the methods of geological inquiry and the fundamental properties of earth systems. As with many modern public scientific debates, they are described erroneously or misleadingly.

Projections for accelerating sea level rise in the 21^st century are soundly grounded in geological investigations of past sea-level change. There is no debate that Quaternary glacial cycles have corresponded directly with large fluctuations of sea level. Periods of rising global temperatures and atmospheric carbon dioxide concentrations trigger glacial melting and sea-level rise, and vice versa. Ongoing world-wide observations indicate that the rates of global temperature change, carbon dioxide level, and glacial melting have accelerated noticeably above the rates observed at the beginning of the 20^th century. All of the factors that influence sea level are occurring at an accelerated rate already.

Sea level is also typical of earth systems in that it is affected by sensitive environmental thresholds, which can trigger abrupt significant change. Our growing understanding of glacier dynamics suggest that glacial melting does not proceed gradually, but that glaciers undergo rapid disintegration. An abrupt increase in the number of rapidly surging glaciers in the last decade indicates that those glaciers have crossed a threshold to more rapid melting, accelerating the addition of water to the oceans. There are no reliable indicators that suggest this trend will reverse. Even more dramatic and wide-spread episodes of glacial melting are well documented in geological studies.

Society has always been slow to respond to creeping crises. One reason that sea-level rise is not perceived to be a serious a problem is because the evidence for past rapid sea-level change –the basis for projecting future rapid change—is being left out of the public discourse.