‘Greenhouse Effect’ contributes to ozone depletion

The hole in the ozone layer over the Antarctic reached its biggest size ever this September, and according to a Chilean scientist, this has been due, among other factors, to the 'greenhouse effect'.

by Gustavo Gonzalez

Santiago,13 Sep 2000 (IPS) -- The unprecedented thinning of the ozone layer over the Antarctic this September is due, among other factors, to the greenhouse effect, said Sergio Cabrera, a scientist at the University of Chile.

The United States National Aeronautics and Space Administration (NASA) found that on Sep 3, the hole in the ozone layer had reached its biggest size ever: 28.3 million square kms—larger than Europe and South America combined.

The stratospheric ozone layer, located 15 to 50 kms above the earth’s surface, filters the sun’s harmful ultraviolet-B (UV-B) rays, which cause skin cancer and cataracts, lead to lower crop yields and damage the marine food chain, starting with microscopic plankton in the world’s oceans.

The hole, which is constantly being measured by satellite images, is a fluctuating oval-shaped area that in the most critical periods extends over the Southern Cone of the Americas, as it did on Sep 3, when it spread beyond Cape Horn, all the way up to Tierra del Fuego, an archipelago located south of the Strait of Magellan.  The region covered by low total ozone begins to grow each year in early August, and peaks in September and October, in the southern hemisphere in spring-time.

At that time of the year, the combined effect of low temperatures at the South Pole and high levels of solar radiation lead the microparticles of ice in the stratosphere over the Antarctic to activate chlorofluorocarbons (CFCs), halons and other substances that trigger ozone-depleting chemical reactions.

The largest hole previously documented -- 27.2 million square kms— was registered on Sep 19, 1998.

At that time, experts predicted that the phenomenon would begin to revert as countries gradually complied with international climate change conventions aimed at reducing the production of ozone-depleting propellents and refrigerants.

But Cabrera, a biologist with the Programme of Cellular Biology at the University of Chile’s Faculty of Medicine, told IPS that such optimistic projections failed to take into account the variable emissions of gases that produce the so-called 'greenhouse effect' or global warming.

Cabrera said the 'greenhouse effect', caused by emissions of carbon monoxide and dioxide as well as other gases, compounded the effect of the ozone-depleting substances, and retarded the recovery of the ozone layer.

He concurred with the Geneva-based World Meteorological Organisation’s warning that it would take 40 or 50 years for the ozone layer to return to the levels registered in 1970, when the thinning process began.

Emissions of CFCs suspended in the stratosphere affect the ozone layer for 40 to 50 years, and although products currently used to replace those substances are not totally harmless for the ozone layer, their effects last only around seven years, he pointed out.

The state of the ozone layer is measured in Dobson Units (DU), and readings below 225 DU indicate levels of ultraviolet radiation dangerous to living beings.

Scientists at the University of Magallanes, located in Punta Arenas, 2,500 kms south of Santiago, have reported measurements of 300 DU over the city. But at the Chilean bases in the Antarctic peninsula, readings ranged between 250 and 150 DU.

Dr. Claudio Casiccia, the coordinator of the Ozone Laboratory at the University of Magallanes, told the Chilean daily ‘El Mercurio’ that the situation at the extreme southern tip of Chile would remain critical until October.

Casiccia did not rule out the possibility that the hole could grow even wider in the next few weeks, perhaps reaching as far north as the region of Ais’n, some 1,500 kms south of Santiago.

Cabrera, however, said that possibility was remote, because masses of stratospheric air with high concentrations of ozone circulate around the edges of the hole, operating as a barrier that curbs its expansion.

But he did warn that the increase in ultraviolet radiation was a real and serious threat for the inhabitants of Argentina and Chile, the two southernmost countries in South America.

It is essential, he said, that anyone living south of the city of La Serena, located 460 kms north of Santiago, “should avoid direct exposure to the sun between 11 AM and 5 PM, or use sunscreen with a factor of at least 15. And children must especially be protected,” Cabrera stressed.

Health authorities also recommend that residents of Punta Arenas and other cities at the extreme southern end of the continent use dark sunglasses whenever they go outside.-SUNS4740