Ice sheets, particularly those in Antarctica, are well-studied because of their potential benefits and the possible associated hazards. Ice sheets captured the atmospheric conditions, especially carbon dioxide levels, during the course of their formation, and are thus records of the Earth’s recent geologic past. On the other hand, ice sheet mass loss due to instabilities and melting brought about by high global temperatures raises alarm and concern over different countries, particularly those in the low-lying shoreline areas.
Ice movement and mass loss are therefore active and interesting areas of geological research and, given the current rise in temperature levels on the planet, are also urgent and important. The science journal Science published a special edition featuring research papers on the current state of the Polar Ice. The introductory editorial by Kennedy and Hanson gives us insight into how the Antarctic ice sheets developed, and their relationship with temperature and carbon dioxide (CO2) levels:
The relationship between greenhouse gas levels and temperature, evident in data from ice cores, illuminates climates in the geological past and may be a more useful guide to the future. Fifty million years ago, CO2 levels may have topped 1000 parts per million by volume (ppmv) and sea levels were about 50 meters higher than those today. CO2 levels gradually decreased as marine organisms fixed carbon through photosynthesis and then buried it by sinking into the ocean basins.
This reduction and a corresponding decrease in temperatures allowed ice sheets to develop in Antarctica starting 30 to 40 million years ago. By 3 to 4 million years ago, CO2 levels probably dropped to or below the preindustrial level of about 290 ppmv, and permanent ice sheets appeared in the Northern Hemisphere. As subsequent glaciations came and went, CO2 concentration and temperature were tightly linked. When both went down, ice sheets grew and sea levels sank, lower than today’s by more than 100 meters.
When both went up, there were relatively stable warm periods with high sea levels (1673). Even before the turn of the century, mass loss in Antarctic ice has been associated with rise in sea levels (Warrick and Oerlemans 1991). Near the end of the 20th century, a research article by Oppenheimer described the potential threat of anthropogenic (human-induced) climate change to Antarctica, the West Antarctic Ice Sheet (WAIS) in particular. The WAIS of mass of 3. 8 million km3 covers Western Antarctica, which would otherwise be an archipelago.
It is composed of an inner sheet that is grounded, or touching land underneath the sea, and an outer part called ice shelves that float over the waters. These sheets are separated by a grounding line. It should be noted that ice shelves float over the water, and thus will not displace water upon melting, hence will not contribute to water level rise. Conversely, grounded sheets will displace water upon melting or release, and their movements are thus more important to analyze when detecting water level rise.
Oppenheimer reviewed the geophysical models proposed for WAIS and compared them with existing experimental data, and predicted a four- to six-meter rise in sea levels when this is released as a whole to the oceans. Sadly, Oppenheimer noted, “atmospheric accumulation of greenhouse gases over the next 100 years could irreversibly affect the future of WAIS” (Oppenheimer 325). The recent scientific attention on climate change, highlighted by the awarding of the 2007 Nobel Peace Prize on the Intergovernmental Panel on Climate Change (IPCC) and Albert Arnold (Al) Gore Jr.
“for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change,” (Nobel Peace Prize Press Release, 2007) heightened the alarm about the effects of increasing global temperature on the ice sheets and intensified the efforts to mitigate them. In the succeeding sections we review recent scientific literature on the matter, illustrate the current condition of the ice sheets in Antarctica, and describe both qualitatively and quantitatively the effects of mass loss in these ice sheets, particularly on sea levels.
The Science editorial mentioned earlier states the special importance given to the topic: “A central feature of this long baseline is this: At no time in at least the past 10 million years has the atmospheric concentration of CO2 exceeded the present value of 380 ppmv” (Kennedy and Hanson 1673). The implication of this carbon dioxide concentration is that sea levels are expected to rise by levels which could be a number of meters above the present level, due to ice melting, consistent with Oppenheimer’s analysis.
Results of new studies also support this idea. Consider, for example, the research conducted by Overpeck, et al. , published in the same volume. Their data suggests that portions of the Antarctic ice sheets are vulnerable to the temperature increase brought about by the corresponding increase in CO2 levels; by 2100, they project, temperature levels will be the same as in the Eemian period 130,000 to 127,000 years ago, when sea levels rose to several meters higher than the present levels (Overpeck, et al. 1747).
A more quantitative study by Velicogna and Wahr showed Antarctic ice sheets decrease significantly, particularly those from the WAIS (also the subject of Oppenheimer’s study), by a rate of 152 ± 80 cubic kilometers of ice per year, corresponding to 0. 4 ± 0. 2 millimeters of global sea-level rise per year (Velicogna and Wahr 1754). Although this points to a lower sea level rise (at about 40 mm in 2100), it has established the direct and positive correlation between temperature and sea level rise due to Antarctic ice sheet mass loss.
If CO2 levels will increase at a faster rate, then this could also point to an earlier projection of a few meters of sea level change. These recent results clearly suggest that high amount of carbon dioxide emissions from our industrial age is now taking its toll on Antarctica. These realizations pose a challenge to scientists, as there are issues still unresolved: Is the ice sheet mass loss that is happening right now part of a cycle that repeats at regular intervals in geological history?
Or is this slowly becoming an irreversible process that will threaten our existence? This in turn will present an equally challenging task for world leaders in implementing policies that would mitigate the effects of global warming. As of the moment, more scientific data are needed to guide us in doing the best move for the Antarctic ice sheets, and, ultimately, our planet.
Kennedy, Donald and Hanson, Brooks, “Ice and History,” Science, Vol. 311 no.5768 (24 March 2006): 1673. Nobel Peace Prizes: See http://nobelprize. org/nobel_prizes/peace/laureates/2007/press. html. Retrieved 11 May 2008. Oppenheimer, Michael. “Global warming and the stability of the West Antarctic Ice Sheet. ” Nature 393 (28 May 1998): 325-332. Overpeck, Jonathan T. , Otto-Bliesner, Bette L. , Miller, Gifford H. , Muhs, Daniel R. , Alley, Richard B. , Kiehl, Jeffrey T. “Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise.
” Science, Vol. 311 no. 5768 (24 March 2006): 1747 – 1750. Velicogna, Isabella and Wahr, John. “Measurements of Time-Variable Gravity Show Mass Loss in Antarctica. ” Science, Vol. 311 no. 5768 (24 March 2006): 1754 – 1756. Warrick, R. A. , and H. Oerlemans, Sea Level Rise, in Climate Change: The IPCC Scientific Assessment, ed. J. T. Houghton, G. J. Jenkins, and J. J. Ephraums. Cambridge: Cambridge Univ. Press, 1991.Sample Essay of StudyFaq.com