---taken from: Whyte, Ian D. Climate Change and Human Society. New York: Halsted Press, 1995.
One of the more widely discussed and potentially more drastic of global impacts in a globally warmed world is the rise of average global sea levels. The combined effects of the thermal expansion in volume due to warming ocean temperatures and the melting of glaciers are forecast to raise sea levels 0.5 to 1.5 meters over the next 50 to 100 years, endangering coastal and low-lying cities, countries, and islands around the world (Newton 13).
As Earth's temperatures have risen, most polar regions have warmed much more than the global average---an expected occurrence in a greenhouse warmed world (Whyte 117). Because of this increased warming, large sections of ice shelves in the Antarctic Peninsula-- ice that has been stable for at least 400 years-- have broken up recently (Hileman 16). "We have evidence that the shelves in this area have been on retreat for 50 years,"says David Vaughan, a researcher with the British Antarctic Survey, "with cumulative losses amounting to about 7000 square kilometers" (qtd in Hileman 18). With news of the retreat of 3,000 square kilometers in a single year, this breakup has proven to be highly unusual. While normally releasing only a few large icebergs in any given year, the calving of the ice shelves into thousands of small icebergs at once is another anomolous occurrence. This ice has no effect on sea level, however, because it has already been floating on the ocean. On the other hand, if increased warming continues, the melting will move further south, exposing inland ice sheets to shrinkage and adding to the ocean's volume. Significant melting of ice sheets could thus contribute to a rise in sea level.
Moreover, the melting polar ice will reflect less of the sun's radiation and in turn have the potential to enhance the greenhouse effect. In fact, scientists are concerned over this and all other potential for positive feedback mechanisms-- responses to change that would greatly enhance the greenhouse effect. Some fear that warmer oceans could be less efficient absorbers of CO2, release tons of methane stored in sea floor mud, or even, through evaporation, release more water vapor into the air. The release of water vapor would be an even bigger problem because it is an even more efficient absorber of heat than CO2 (Bernard 81). An additional feared positive feedback mechanism is that increased temperatures will accelerate the decay of land-based organisms without changing the rate of photosynthesis, according to Richard Houghton and George Woodwell, researchers at Woods Hole Research Center in Massachusetts. This could potentially lead to increases in both carbon dioxide and methane concentrations in the atmosphere (Bernard 81).
