The release of gases from our activities has enhanced the natural greenhouse effect. The trend of increasing CO2 has been recorded since 1860 and deforestation and the consumption of fossil fuels are our main activities that involve its release.
Solar radiation reaching the earth's surface is partly absorbed, and partly reflected as lower-energy infrared radiation. Oxygen and nitrogen, the most abundant gases in the atmosphere, do not absorb this reflected radiation, whereas water vapor, carbon dioxide, methane, nitrous oxide, chloromethane and ozone do.
This results in a greenhouse effect due to natural causes, which keeps the earth's surface under a certain temperature range.
But the release of gases from our activities has enhanced the natural greenhouse effect. The trend of increasing CO2 has been recorded since 1860 and deforestation and the consumption of fossil fuels are our main activities that involve its release.
On the other hand, there are feedback mechanisms that can enhance or counteract the effects.
Water vapor is the substance that absorbs and emits more infrared radiation in the lower atmosphere, and its concentration increases as global warming increases.
The most valuable information on changes in CO2 concentration comes from various observatories located at strategic points, isolated from external agents of gas production and representative of large air masses, whether in oceanic or continental areas.
The Antarctic continent is an environment that meets these characteristics. In addition to the almost zero release of gases by human activities, the very scarce terrestrial vegetation is added: the variations that could cause changes in the concentration of carbon dioxide practically do not interfere.
Currently there are 15 stations that take continuous records in the world, and three of them are in Antarctica. At our Jubany base, located on 25 de Mayo Island (South Shetland Islands); at the Syowa base in Japan; and at the Amundsen Scott base in the United States, located at the South Pole. Among other things, the data make it possible to compare variations between winter and summer, day and night, and the effects of the wind.
On the other, our country began studies on related issues aboard the A.R.A. Admiral Irizar. In February 2000, a project began under an agreement between the Argentine Antarctic Institute and the Pierre and Marie Curie University of
Paris to study the flux of carbon dioxide between the atmosphere and the sea, and its influence on the marine plankton communities.
As a consequence of this global trend of increasing CO2, increases in temperature are being recorded. From the analysis of the records from different bases, an increase in temperature has been detected from the Orcadas base towards the Antarctic Peninsula, and at the present rate, this would mean an increase of 1º C in 20 years.
From recent glaciological studies on the continent, there is concrete evidence of the retreat of glaciers and ice shelves. The immense breach of the Larsen barrier in the summer of 2002 stands out.
One of the most obvious consequences of the increase in temperature and consequent retreat of the land ice is the change in the level of the sea, although there are other variations that will be less evident, such as those that occur in ocean currents.
During the glacial periods, with temperatures between 3º C and 5º C lower than the current ones, the sea level dropped to 100 m below the current one.
100,000 years ago there was the last interglacial period, with temperatures between 2 and 3º C higher than the current ones and sea levels between 5 and 7 meters higher.
Currently the water level is rising at an average of 2 mm per year, while it has been determined that in the last 5,000 years the increase was in the order of 1 mm per year.
Prediction calculations indicate that the melting of the ice would cause a rise of up to 1.5 m in the level of the sea in the next 50 years.
Effects on terrestrial vegetation of Antarctica
Warming (since 1950, in the Antarctic Peninsula the average air temperature in summer has risen 1º C; see page 00) acts differently on the Antarctic grass (Deschampsia antarctica; grass) and on the so-called Antarctic carnation (Colobanthus quietensis ; Caryophilic family) and would be cumulative between seasons.
Parameters such as photosynthesis rate, plant growth rate, and reproductive success help to evaluate changes. The reproductive structures of both species had more development or more maturation with increases in temperature. Colobanthus produced a greater number of seeds due to reproductive structure, although the seeds were not more viable or heavier.
More than 30 years of monitoring populations of these flowering plants on subantarctic islands showed an increase in their abundance. It has been suggested that the warming of the air during the summer has facilitated the maturation of its seeds, the germination, and the survival of seedlings. It is also known of its expansion in the Antarctic Peninsula, at least since the last five years.
Continuing with the monitoring and studies will shed new light on these issues.
* Santiago G. de la Vega
Lic. In Cs. Biological