The ozone hole over Antarctica grew to the size of North America in 2008 – the fifth largest on record – according to the latest satellite observations. Scientists from the National Oceanic and Atmospheric Administration (NOAA), the United States, say the ozone hole reached its maximum level on 12 September 2008, extending to 27.2 million sq. km and 6.4 km deep. That is bigger than 2007 but smaller than 2006, when the hole covered over 29.5 million sq. km.

Expressing the same fear, Mr. Geir Braathen, ozone specialist at the World Meteorological Organization, said the ozone hole will reach at least a size of 27.9 million sq. km in area. He noted that although there has been a notable decrease in ozone-depleting substances, their atmospheric concentration was still high. “Even if chlorine and bromine are coming down, there is still for many years to come enough of these substances to deplete all the ozone in this height range,” he opined.

Scientists blamed colder-than-average temperatures in the stratosphere for the ozone hole’s unusually large size this year. “Weather is the most important factor in the fluctuation of the size of the ozone hole from year to year,” said Mr. Bryan Johnson, a scientist with NOAA’s Earth System Research Laboratory, which monitors ozone, ozone-depleting chemicals and greenhouse gases around the globe. “How cold the stratosphere is and what the winds do determine how powerfully the chemicals can perform their dirty work.”

Starting in May, as Antarctica moves into a period of 24-hour-a-day darkness, winds create a vortex of cold, stable air centred near the South Pole that isolates CFCs over the continent. When the spring sunshine returns in August, the sun’s ultraviolet light sets off a series of chemical reactions inside the vortex that consume the ozone. The colder and more isolated the air inside the vortex, the more destructive the chemistry. Then, by late December the southern summer returns in full swing, the vortex crumbles, and the ozone reforms – the process begins anew the following winter.

Source: www.guardian.co.uk and www.msnbc.msn.com

Evidence presented in France seems to indicate that the hole in the ozone layer above Antarctica impairs the ability of the Southern Ocean to absorb carbon dioxide of the earth’s atmosphere. The oceans of the Earth are the largest absorbers of carbon dioxide on Earth, and the Southern Ocean is thought to take up more than 40 per cent of the carbon dioxide absorbed by oceans, according to Mr. Andrew Lenton, a marine biologist at the Pierre and Marie Curie University in Paris, France.

Theoretically, the more carbon dioxide the atmosphere contains, the more the oceans should absorb. However, recent measurements have shown that the surface waters of the Southern Ocean actually contain more carbon dioxide than expected. This also makes them more acidic. The amount of carbon dioxide that is being absorbed also flattens out at this time. Mr. Lenton says that stratospheric ozone damage was missing from the models made thus far. Yet, it is thought to have an effect on the strengthening of the Southern winds, alongwith the effects of greenhouse gases on the climate. He thinks that these stronger winds are causing ocean currents that bring carbon that is stored in the deep ocean up to the surface.

Mr. Lenton and his colleagues have built simulations of the Southern Ocean that take the effect of ozone into account. By including the ozone hole in the model, they were able to reproduce the feeble absorption of carbon in the Southern Ocean that oceanographers have measured. However, researchers from the Leibniz Institute of Marine Sciences in Kiel, Germany, say that they question the changes in ocean currents shown by models such as those made by Mr. Lenton and that oceanographic data provides no hard evidence for these changes.

Source: www.digitaljournal.com