Sea Level Rise Signals Global Warming
Coasts, Ecology, Environments Threatened
History of Sea Level Rise
Though of concern now, the rise and fall of the sea's relative level is actually nothing new to the planet. V. Gorniz analyzes the historical aspects of global sea level rise in his article "Earth Surface Processes and Landform." His research indicates that the most recent geological trend in sea level rise began sometime around 18,000 years ago. Not long after the Last Glacial Maximum the oceans were estimated to be 130 meters lower than today. Sea level has exhibited a steady rise ever since, gaining total altitude equal to one and a half football fields.
However, alarming recent data from new more accurate satellite technology indicates a sudden increase in sea level rise over the past century. According to the TOPEX/Poseidon mission launched by NASA’s Jet Propulsion Laboratory, the mean sea level is rising by about 3 mm per year-- 3 times previous measured estimates made by tide gauge data.
Global Warming and Sea Level Rise
Varied causes make up the reason for sea level rise. However, according to numerous studies including one sponsored by the American Meteorological Society by Church et al., a process known as thermal expansion has the greatest effect on sea level rise in recent times, and is theorized to have the greatest impact on future sea level rise. As water heats up due to global warming, it expands in volume, causing the sea level to increase. Volumetric thermal expansion will have an additional effect on sea level as glaciers, ice sheets, and ice caps melt and add water to the ocean.
By How Much Will the Sea Level Rise?
The International Panel on Climate Control (IPCC), a global partnership of climate scientists, concluded a global average sea level rise about between 19 and 89 centimeters over the next century, mainly due to thermal expansion and largely spurred by anthropogenic global warming. Local sea level changes will be highly variable.
International Panel on Climate Control Predicts Disaster
In the United States, the most vulnerable region is the Gulf Coast, especially Louisiana. The recent report by the IPCC estimated costs of a one meter sea level rise in the U.S. to be between $275 and 400 billion. If no preventative measures are taken, a one-meter sea level rise would result in the loss of 14,000 square miles of US coastal land.
Global Effects: Economy, Displacement
Other vulnerable areas include unprotected delta regions of Bangladesh, Egypt, and Vietnam which are estimated to be home to 8-10 million inhabitants within one meter of sea level. Already, significant climate impacts are being seen in some of these areas. In addition, about half a million island nation inhabitants are are especially vulnerable to coastal erosion and storm surges that will magnify flooding. Several regions will feel the effect through changes in marine ecology, including the fish market. Sydney, Shanghai and coastal Louisiana are all economically dependent on fisheries.
Scenarios Still Widely Variable At This Point
While doom-and-gloom scenarios must be considered, some reports remind us that the effects of sea level rise will most certainly be highly variable, since the economic, social and biological resiliencies are unknown for many projected effects.
Also highly variable are projections on how much sea level will rise in the near future, however even the short term conservative estimates of a sea level rise of up to 70 cm based solely on a 3-4°C global mean temperature increase could have a significant impact on coastal communities. A realistic scenario beyond the 100 year position depends heavily on what actions are taken to help control global warming.
Sources
How Fast Are Sea Levels Rising? by John A. Church (26 October 2001) Science 294
Sea levels: abrupt events and mechanisms of change. by R. Edwards (2005) Progress in Physical Geography 29
Sea level is rising: Do we know why?. by M. F. Meier and J. M. Wahr (2002)PNAS 99
Sea-level rise: A review of recent past and near-future trends by Gornitz, V. Earth Surface Processes and Landforms. Vol. 20, no. 1, pp. 7-20. 1995
