An Overview of the Causes and Effects of Sea Level Rise
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Global Sea Level Rise Is Accelerating - Study | UNFCCC
Baca , Mark L. Titus ; other contributors, Timothy W. Timothy W. Kana , James G. New Jersey case study.
Kana , William C. At the current rate, the rise of the level of the oceans of about 3 millimeters per year right now could more than triple to reach 10 an extra millimeters per year by This would mean that the sea level could rise by 65 centimeters by the end of the century, a figure in line with estimations by the UN Intergovernmental Panel on Climate Change, with serious implications for coastal cities and small island states such as Fiji. Climate change is driving ocean rise through two phenomena: the rapid melting of ice at the poles and the increased concentrations of greenhouse gases in the atmosphere.
This latter phenomenon warms the temperature of the water.
This global sea-level rise often termed Eustatic sea-level rise has three components:. Other phenomena can substantially influence sea levels at regional scale, inducing either sea-level rise or sea-level fall . Most important are:. Due to these phenomena, sea-level rise is not uniform around the globe, but differs from place to place. Relative sea-level rise is the locally observed rise of the average sea level with respect to the land level. It is the sum of the components Trends in sea-level from world-wide available tide gauge records and from satellite measurements have been analyzed by Church and White .
The tide gauge data were corrected for vertical land surface motion, by using estimates for glacial isostatic adjustment assuming that this is the major cause of vertical land surface motion.
Sea Level Rise
From these corrected tide gauge data, a linear trend of 1. Trend analyses of regularly updated satellite data can be viewed at the NOAA site  for global and regional sea-level changes around the world. Even after correcting for the effect of glacial isostatic adjustment, substantial regional differences in sea-level rise occur .
Major causes are:. There is hardly any doubt that the global sea level has risen faster during the past decades than in the past century. The estimated global sea-level rise for the past decades is based on satellite altimeter data and estimates of different contributions to the ocean water budget especially melt of the Greenland and Antarctic ice sheets. A much higher than average sea-level rise is observed in the Indian Ocean—Southern Pacific region. This regional feature has a strong impact on the estimate for the global sea-level rise .
However, uncertainties remain in the calibration of the satellite altimeter data. A much lower acceleration rate of 0. No acceleration of sea-level rise is visible in these data. This can be partly due to changes in the gravitational field the influence of the decreasing ice mass of Greenland may account for a 0. Many model studies have been conducted to predict future sea-levels. Different forecasts of future sea levels display a large spread. This is due to uncertainty regarding future emissions of greenhouse gases, to shortcomings in the present understanding of climate dynamics including ocean-atmosphere interaction and to restrictions imposed on model grid scales.
All models predict an increase of the rate of sea-level rise. Projections for the main components of sea-level rise according to different scenarios and different models are presented in Table 1. Sea-level rise lags behind global warming. Even if greenhouse gas emissions would stop today, sea levels will continue rising for at least a century . In the hypothetical case that there will be no greenhouse gas emissions from now on, sea levels will be 0.
It has been suggested that the contributions from the Antarctic to sea-level rise could be much larger when considering structural collapse of the marine-terminated ice cliffs and disintegration of the West Antarctic ice sheet after removal of the ice shelves  . This could contribute to an additional sea-level rise of 1 m in and up to 15 m in However, some doubts exist whether marine ice-cliff instability is a realistic scenario .
Hansen et al. This feedback process is triggered by increasing amounts of fresh meltwater from the polar ice sheets that strengthen ocean stratification, reduce the sinking of Antarctic cold water and decrease the ocean heat flux to the atmosphere. This results in sequestration of warm deep water and enhanced melting of the Antarctic ice sheets.
follow site These authors also predict a slowing of the Atlantic meridional overturning circulation AMOC due to increasing meltwater outflow from the Greenland ice sheet, with possibly important consequences for the North Atlantic Gulfstream and the climate of northwestern Europe. A more detailed discussion is presented in the articles Ocean circulation and Thermohaline circulation of the oceans.
Most coastal zones are more vulnerable to extreme sea levels than to the mean sea level. This holds in particular for coasts situated on broad continental shelves North Sea, East China Sea, for example where extreme levels are much higher than the mean sea level, due to amplification of the ocean tides and water-level setup by strong winds storm surges.
Nevertheless, rise of the local mean sea level is always the major component of the projected rise of the local extreme sea level for any given long return period. However, climate-induced change in extreme wind and wave conditions can influence extreme sea levels significantly in some regions  . Along the eastern African coast extreme wind and wave conditions will be less frequent, whereas in northern Europe especially the Baltic region in the RCP8.
Sea-level rise does not only affect extreme sea levels, but also the average return period. This will be the case in particular for coasts situated close to the deep ocean, where sea levels are less influenced by storm surges, and for coasts outside the zone of tropical cyclones. For these coasts the average return period of extreme sea levels will strongly decrease; in many cases a reduction of a factor greater than is projected in the IPCC scenario RCP8.
For coasts situated on broad continental shelves where extreme levels are much higher than the mean sea level, the average return period will be reduced by a factor 10 or more  . For uplifting coasts the reduction of the average return period will be less, because of a smaller relative mean sea-level rise. Sea-level rise will have a great impact, in particular on low-lying coastal regions, such as river deltas and coral islands  . Delta coasts and coral islands are shaped under the influence of marine bio-geomorphological processes; their natural elevation is therefore around the present high water level — not much higher and sometimes lower.
Many low-lying coastal zones are densely populated and host large cities; a large number of coastal megacities are located in developing countries . Considerable investments are required for adapting these vulnerable coastal zones to sea-level rise, in particular to reduce flooding risks . Sea-level rise enhances shoreline retreat for retreating coasts or reduces shoreline progradation for accreting coasts , see Natural causes of coastal erosion.
The influence of sea-level rise on the shoreline position of sandy barrier coasts can be estimated by means of the Bruun rule . Sea-level rise also threatens coastal wetlands, which may not be capable to keep pace with sea level and be partly lost due to so-called coastal squeeze. This can be the case for mudflats and salt marshes in the Wadden Sea  and for mangrove forests in the tropics and subtropics, see Potential Impacts of Sea Level Rise on Mangroves.
Salt intrusion is another major impact of sea-level rise in low-lying river deltas around the world. This impact is compounded by soil subsidence and by reduced fresh water supply to the coastal zone due to upstream diversion of river water for irrigation and other uses. Salt intrusion threatens crucially important fresh groundwater reservoirs in arid regions, for example in the Nile Delta . Relative sea-level rise also causes loss of fertile agricultural land in the coastal hinterland by increased salt seepage to surface waters  , with great economic and social consequences.
Salt intrusion further affects drinking water availability in densely urbanized coastal regions.