Scientists probe the ozone hole for clues to its cause
Punta Arenas, Chile
AUGUST is miserable at the end of the earth. While cities north of the equator swelter under the late summer sun, this community of 100,000 at the southern tip of South America shudders through the last stages of another harsh winter. Some days, the biting wind and the cold, driving rain blow so fiercely off the Strait of Magellan that merely crossing the street requires meticulous preparation. Then, late in the month, the skies clear, and by early September the winds die down to a tolerable bluster. And in recent years, something else happens to the air at the bottom of the world: In the stratosphere high above the Antarctic, the earth's protective layer of ozone begins to disappear, creating an irregular ``hole'' roughly the size of the United States. In about three weeks, much of the ozone in this area is destroyed, stripping away the planet's best defense against damage caused by the sun's ultraviolet rays.Skip to next paragraph
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More of this protective shield disappeared last month than has been recorded before - a 50 percent loss between mid-August and mid-September, according to Robert Watson, chief of NASA's high-altitude research program. Ozone levels fell to 35 percent last year during the same period, and to 40 percent in 1985.
Scientists have been talking about ozone depletion since the mid-1970s, but the ultimate threat posed by the Antarctic hole - destruction of ozone globally - has given the problem a new sense of urgency. Scientists fear that a major loss of ozone could lead to dramatic increases in skin cancer and cause crop failures and climate changes.
This year, a team of 150 scientists, engineers, NASA technicians, and pilots set up shop in a chilly military hangar here in the most ambitious examination of the ozone hole to date. They brought several tons of scientific equipment to conduct some 21 experiments, collecting extensive data from two specially equipped jets, ground measurements in Antarctica, and satellites passing overhead. The magnitude of the NASA expedition has raised expectations that the scientists will come up with some definitive answers to explain the cause of the mysterious hole.
So far, the preliminary findings announced by Dr. Watson last Wednesday point to the combined effect of man-made chemicals, principally chlorofluorocarbons (CFCs), and the extreme cold over Antarctica at the beginning of the Southern Hemisphere spring as the cause of the ozone hole. Scientists will study the data for another six months before issuing a final report. ``This is the most important earth science experiment of the decade,'' said Watson.
Threatened by the results is the $100 billion worldwide CFC industry, which has balked at developing alternatives for the chemical compounds, made primarily of chlorine, fluorine, and carbon. Ironically, what has made CFCs so useful - their stability - may be the very reason they now threaten the environment. The compounds are so safe - they aren't toxic, flammable, or water-soluble - that they survive for decades. Eventually they reach the stratosphere, where they are broken down by the sun's ultraviolet rays. Once released from its chemical bond, the chlorine in CFCs attacks ozone.
The ozone hole was first confirmed in 1985 by British scientists stationed on the Antarctic coast. The British team had noticed a dramatic drop in ozone levels 10 years ago, but the measurements were so abnormal that they were attributed to computer or human error. But the measurements were later corroborated by a second British station 1,000 miles away, and last October American scientists at McMurdo Station on the Antarctic Peninsula concluded that chemicals, primarily CFCs, were responsible for the hole.