One of the points on the globe which is suffering most clearly from the first effects of global warming are the glaciers of Antarctica. Amongst these formations, those that are reacting most quickly to the increase of a few tenths of a degree in temperature are those located at the edges of the white continent, stuck to the coast, which are usually thinner and constantly exposed to temperatures close to their melting point (0°C). In a recently concluded work, researchers from the Federal University of Rio Grande do Sul (UFRGS) and Freiburg University, Germany, produced the most complete and updated digital map of the topography of one of these sensitive fragments of ice-covered land: King George Island, which houses the Brazilian base in Antarctica and another eight research stations, 120 kilometers to the north of the Antarctic peninsula.
Generated from cross-checking a series of sources of information – remote sensoring images supplied by the European SPOT satellite, data produced in recent field research with a GPS (Global Positioning System) device, consultations with topographical maps and with the digital database on the continent maintained by the British Antarctic Survey -, the new map is an important instrument for carrying out studies into glaciers, climate, and the environment management.
Comparing the details of the current map with old geographical charts, the researchers found that an important group of the island’s glaciers has lost 10% in length in a little less than half a century. Between 1956 and 2000, the masses of ice from Admiralty Bay, the region chosen for the study – where, incidentally, the Brazilian research station is – shrank 22,5 square kilometers.The information refers to the tidal glaciers, which face the sea and are subject to the action of the ocean.
But there is no evidence that the shrinkage of the masses of ice in the bay is due to changes in the dynamics of the tides. “The magnitude of this reaction indicates that the process is not part of the natural dynamics of forward and backward movements of glaciers”, says Jefferson Cardia Simões, head of UFRGS’s Laboratory of Antarctic and Glaciological Research (Lapag) and one of the authors of the map. “These masses of ice are probably responding to an increase in the temperature in the region”.
Warming
The degree of definition of the virtual map produced by the Brazilians and the Germans makes it possible to monitor alterations in areas as small as 0,5 square kilometers, with a resolution at least five times greater than with the old maps. With 1,157 square kilometers (80% of the area of the city of São Paulo), King George Island, warming up and with its glaciers melting, does not generate large icebergs, like those that spend months or even years wandering the seas, endangering marine animals populations. One example is B-15A, a mass of ice of 5,400 square kilometers (three municipalities the size of São Paulo) which broke loose from Antarctica in March 2000 and today torments colonies of Adelie penguins (Pygoscelis adeliae) in the Ross Sea, to the west of the continent.
Even so, the shrinkage of the glaciers on the island – almost 93% of the territory of King George Island is covered with ice and snow – may produce regional impacts, besides sending a clear sign that the climate there is really changing. Locally, the drawing back of the glaciers makes new areas of firm ground arise on the island, free of snow, creating a favorable environment for colonies of animals to arise. After all, there is now exposed rock where there used to be ice. “The drawing back of the glaciers may affect aquatic life”, says Jefferson.
The environmental impact may be worsened by the ample presence of researchers and tourists (4,000 each summer) on the island, one of Antarctica’s accessible points. It is part of the South Shetlands archipelago, some 900 kilometers from Tierra del Fuego, the southernmost point of South America. The pattern shown by the glaciers of King George Island drawing back in the second half of the 20th century strengthens the hypothesis that the melting is due to the warming up of the climate. In four and a half decades, the speed of drawing back seems to increase as the warming up becomes more evident, above all after the 70’s.
The figures corroborate this line of thought. Between 1956 and 1979, 4,3 square kilometers of masses of ice disappeared from Admiralty Bay. Practically the same area of glaciers (4,9 square kilometers) was dispersed between 1979 and 1988, a period that does not even come to half of the previous one. Between 1988 and 1995, a mere eight years, the pace intensifies, and another 6,2 square kilometers of masses of ice disappeared. Finally, from 1995 to 2000, the last and most recent period analyzed, the size of the shrinkage was the largest of the whole historical sequence: 7,1 square kilometers.
What is surprising is that the villain of the story may be the piffling increase of 1.08% in the average temperature on King George Island, recorded between 1947 and 1995, according to the data from the Lapag researchers.It may seem little, but it is a lot: almost twice the average increase in the temperature of the Earth verified over the last 100 years, which was 0.6ºC. In the Antarctic peninsula, between the latitudes of 65º and 70º south, a region a little more to the south than King George Island, the warming up was even higher: around 2ºC over the last 50 years.
There is a consensus that this region, at the edge of the continent, is undergoing a process of warming up. As to Antarctica as a whole, there is conflicting data: a study published in the English magazine Nature (31/1/2002 issue) states that, instead of having increased, the average temperature of the continent, above all in the summer and autumn months, diminished slightly between 1966 and 2000.
Greenhouse effect
It is generally believed that global warming is a consequence of the increase in the greenhouse effect, raising the temperature of the atmosphere. The greenhouse effect is natural, necessary for life: without the curtain of gases in the atmosphere, in particular carbon dioxide (CO2) and methane, which retains part of the energy emitted by the Sun, the globe would be cold and inhospitable.
The problem is that the brutal increase in the concentrations of CO2 in the atmosphere since the beginning of the Industrial Revolution – from 280 ppm (parts per million) in 1850 to 370 ppm today – tends to intensify the greenhouse effect. Some forecasts point to the possibility of the Earth’s temperature increasing another 3ºC by the end of the century. The melting of the glaciers in Antarctica, in the Arctic Ocean and in Greenland is likely to intensify , which will mean an increase of up to 90 centimeters in the level of the sea by 2100, capable of causing the flooding of coastal cities all over the world.
A hypothesis on the wrong side of the road
A study published in the American magazine Science (January 18th issue) checkmates a trend in the interpretation of climatic phenomena that has taken shape over recent years in terms of Antarctica: that the layer of ice and snow that covers the continent almost entirely is melting as a result of the warming up of the Earth’s climate. Carried out by researchers Ian Joughin, from the California Technology Institute, and Slawec Tulaczyc, from California University, the new work shows an increase in the thickness of the reef of ice in the Ross sea, also called the Ross platform, a group of glaciers that covers the west of Antarctica and advances into the Ross sea.
According to the calculations by the pair of scientists, the Ross platform gains between 14,9 and 26,8 billion tons of ice/snow a year. The result contradicts those of previous works, which indicated an annual shrinkage (melting) of up de 20,9 billion tons of ice on the platform. But, according to Joughin and Tulaczyc themselves, the apparent discrepancies between the data from their work and the older measurements can be less than thought, for two reasons.
Firstly: there is wide evidence that in the past the platform really did shrink. Secondly: the thickening of the platform may have little to do with the variations in the temperature of the Earth and be just the fruit of a natural cycle of expanding and shrinking of the glaciers. Under this line of thought, through a stroke of luck, the American researchers must have carried out their measurements at the moment when the tendency towards the glaciers diminishing had given way to an expansion in their mass.
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