Rising sea levels, resulting from global warming, may have a potentially important impact on human culture. Recent evidence supports the contention that increases in greenhouse gases are linked to rising sea levels. One important impact of climate change and rising sea levels is increased rates of extinction across the globe. Further, changes in sea level will have a significant impact on outlying coastal areas, both in terms of physical changes, and in terms of events such as storm surges. Rising sea levels in the United States and across the world will have significant economic and cultural impacts, and may influence human health and the environment through the flooding of toxic waste disposal sites.
Warrick, in his 1993 book, Climate and Sea Level Change: Observations, Projections and Implications, notes that there are many important uncertainties in predicting both global climate change, and changes in sea level. The factors that can impact global climate change include greenhouse gas concentrations and their associated impact on oceanic thermal expansion, ice sheets in Greenland and Antarctica, and mountain glaciers (Warrick, 1993). In the simplest scenario, greenhouse gases like carbon dioxide warm the Earth by absorbing outgoing infrared radiation (Titus et al., 1991).
In any discussion of the environmental impact of sea level changes, particularly in the context of global warming, it should be noted that changes in sea level and climate are natural occurrences. Warrick (1993) notes, "Change in climate and sea level is the rule, not the exception. Natural variations in sea level a clearly evident over a large range of time and space scales, from the pulse of diurnal tides to globally coherent variations in sea level of current over many millennia ... The Earth is a naturally strongly interactive, dynamic system" (p. 3).
As Warrick (1993) points out, the fact that changes in sea level and climate are natural occurrences is often overlooked in the context of discussions of global change. In recent years, atmospheric concentrations of a number of greenhouse gases such as methane, carbon dioxide, chlorofluorocarbons, and nitrous oxide have increased dramatically. As such, these fast and dramatic increases have led to widespread speculation that they can be linked to changes in the global environment. However, a correct and the useful assessment of the problem requires that such changes be considered within the context of normal natural variation in sea level and climate (Warrick, 1993).
In the same breath, the speed and magnitude of the increasing greenhouse gas concentrations gives "rise to legitimate concerns about the future" (Warrick, 1993, p. 3). These include concerns that humankind may be a significant and new factor in the global environmental change that may dominate natural changes, and that changes in sea level and climate could accelerate at unknown rates. Further, there are concerns that the human impact on the global climate may have dramatic consequences, and that accelerated rates of global environmental change may exceed the human ability, and the ability of the natural world, to adapt to such changes (Warrick, 1993).
Based on evidence from coral reefs and oxygen isotopes, the geological time scale suggests that sea level and climate are linked. Sea level fluctuations are associated with transitions between warm interglacial periods and cold glacial periods. For example, during the last interglacial period, approximately 120,000 years before today, the mean global temperature was likely warmer, and the mean the global sea level was likely 526 m higher than today. Similarly, about 18,000 years ago, during the last glacial maximum, global temperature was about four to five degrees colder than today, and the sea level was close to 100 m lower (Warrick, 1993).
In the relatively recent past, sea level changes have been relatively slow and stable. In the last 1000 years, the rise in sea level has been approximately 0.1 to 0.2 mm per year (Warrick, 1993).
Current evidence indicates that glaciers in Antarctica are melting, and potentially may contribute to increases in sea level. A recent study published in the journal Science notices that glaciers in the Amundsen Sea sector of West Antarctica are discharging approximately 250 cubic km of ice into the ocean each year. This is approximately 60% more than the amount accumulated in their catchment basins. The authors note that this discharge alone could increase the sea level by over 0.2 mm per year. Further the authors note that glacial thinning rates observed in 2002 to 2003 are larger than those seen during the 1990s (Thomas, R. et al. 2004).
Interestingly, notes Warrick (1993), different oceanic regions of the world can be affected in different ways by global climate change. This can be linked to redistribution of ice mass during interglacial and glacial cycles (Warrick, 1993).
While evidence clearly seems to indicate that climate changes occurring, and that sea levels are rising, the implications of these changes to the environment and humankind are still somewhat unclear. An investigation reveals that such changes may potentially have catastrophic impacts on biodiversity and low-lying coastal areas, in particular.
Recent evidence suggests that climate change may pose a significant risk of increased extinction rates. In a study published in 2004 in the journal Science, researchers project that 15 to 37% of species in sample regions and taxa will be "committed to extinction" by 2050 (Thomas, C.D. et al., 2004, p. 145). The most positive projection of the study, based on minimal climate warming scenarios, suggests that approximately 18% of species will be committed to extinction by 2050. The authors assessed sample regions that made up approximately 20% of the Earth's terrestrial surface (Thomas, C.D. et al., 2004). Note the authors, "minimizing greenhouse gas emissions and sequestering carbon emissions to realize minimum, rather than mid-range or maximum, expected climate warming could save a substantial percentage of terrestrial species from extinction" (Thomas, C.D. et al., 2004, p. 147.
Low-lying coastal areas around the world will perhaps be some of the regions most highly impacted by changes in sea levels. These regions may feel the effects of climatic change in terms of severe tropical storms and storm surges. Regions most likely to be impacted by rising sea levels include the Netherlands, China's eastern coast and Hong Kong, South America, the Mississippi deltas, the Ganges Brahmuputra, Egypt, Bangladesh, and the Norfolk coast of the United Kingdom (Warrick, 1993).
A significant rise in mean sea level will have a direct physical effect on coastal areas. These include: "coastal or ocean shoreline inundation owing to higher normal tide levels plus increased temporary surge levels during storms, and saltwater intrusion primarily into estuaries and groundwater aquifers" (Sorensen, in Barth and Titus, Chapter 6).
The human impact of increasing sea levels will also be felt in socioeconomic terms, in addition to physical and environmental changes (Warrick, 1993). If sea level rises at what is an estimated to be a 50 to 200 cm in the next century, the financial impact on the United States could be significant. In total, the cost for a one meter rise in sea level during that time would run 270 to 475 billion dollars. This would include the cost of protecting emotion resort communities by raising barrier islands and pumping sand onto beaches, the cost of using dikes and bulkheads to protect developed areas along sheltered waters, and the loss of undeveloped lowlands and coastal wetlands (Titus et al., 1991).
However, the environmental consequences of such actions may prove prohibitive. For example, levees and bulkheads along sheltered waters may eventually eliminate much of America's wetland shorelines (Titus et al., 1991).
Further, there are potentially significant social and cultural applications to measures taken in response to rising sea levels. The coast and local features are tied closely to the mythology of many cultures, and the lifestyles of many people. Importantly, "many people in developed and developing nations view the sea, coasts, reefs, and beaches as…