Sea Level Rise

Abstract

Sea level rise in the twentieth century was 1.7 mm/year, and there are different accounts as to whether the rise included a very small deceleration or acceleration. From 1993 to 2012, altimeters have measured a greater sea level trend than the twentieth century trend, but it is not known yet whether this is the leading edge of a sustained acceleration or a fluctuation similar to others that occurred in the twentieth century. The Intergovernmental Panel on Climate Change (IPCC) projected a sea level rise of 0.18 to 0.59 m from 1990 to 2100, but did not include scaled-up ice discharges from ice sheets of Greenland and Antarctica in determining its 0.59 m upper limit. There have been a number of projections of sea level rise to 2100 of 1 to 2 m. These are typically maximum possible projections that do not have probabilities associated with them and, thus, are not directly comparable to the 95%-confidence level projection of the IPCC. Assuming highly improbable/impossible events such as the immediate collapse of the West Antarctic ice sheet with the simultaneous quadrupling of carbon dioxide levels in the atmosphere, sea level could rise as much as 1.7 m by 2100. However, this maximum possible sea level rise by 2100 is not useful in planning and design of flood projects, since it is not typically used even for siting nuclear power plants. Instead, planning and design of flood projects require statistics of sea level projections that are at commensurate probability levels with design-floods. Although IPCC did not fully consider the contributions from Greenland and Antarctica, a recent study that did uses IPCC methodology and projects 5, 50, and 95%-confidence-level rises by 2100. Assuming a standard normal distribution, these projections can be used to determine sea level rise probabilities that are consistent with design-flood probabilities. Sea level rise by 2100 will have significant effects on permanent coastal inundation, flooding from episodic events, shoreline erosion and salinity intrusion. The most appropriate response to sea level rise is limiting the long-term rise to a manageable level and adaptation to the inevitable rise which will occur. The world must work to reach new agreements limiting carbon emissions and thus limit the long-term rise. But since sea level rise has considerable inertia and will produce an inevitable rise, steps must be taken to adapt to the rise.