National Geographic : 1990 Oct
A smoke signal seen by space shuttle astronauts in 1988 reveals burning of Brazilian rainforest. Used to clear land for farming and ranching, such fires release water vapor, meth ane, nitrogen oxides, and car bon monoxide, as well as CO 2 . The dark, towering feature is the shadow of hot gases rising through a hole in the white, cloud-like pall of smoke. Such a pall over the United States would blanket everything east of the Rockies. Astronauts have seen similar formations over burning grasslands in Mada gascar, Australia, and Africa. Burning wood provides essen tial energy in many developing countries. African nations, on average, gather 70 percent of their energy from wood. With populations soaring, pressures grow ever more acute to burn trees for energy and to clear lands for farming. The hole was real; the ozone had dropped by 50 percent (page 90). Its destruction was confined within the rotating swirl of winds in the polar vortex. And it was caused by a chemical reaction, not some unfathomed atmospheric phenomenon. The reaction seemed to occur in the presence of thin polar ice clouds that form in the intense cold of late winter, just before the sun returns to strike the polar latitudes. Less than a year later, in September 1987, more than 40 nations sent delegates to Montreal, Canada. The industrialized countries agreed to reduce production of CFCs by 50 percent by 1998. A June 1990 revision called for a 100 percent ban by the year 2000, with a ten-year time lag for less developed nations. Does another ozone hole develop over the Arctic in its winter? If the Northern Hemisphere, far more populous than the South ern, is also being depleted of its ozone umbrella, it might pose a far more serious emergency. The same team of atmospheric scientists and computer experts, including Robert Watson of NASA and Adrian Tuck and Susan Solomon of NOAA, spent 45 cold, bleak days in Jan uary and February 1989 in the North Sea port of Stavanger, Norway. There the same ER-2 and DC-8 flew 28 missions, from the northernmost airstrip that could safely be used, to take read ings from the air of the polar Arctic. It took a year to analyze all the data. In March 1990 the scien tists published their answer. The polar vortex and ice clouds existed also in the northern stratosphere, though not to the same extent as in the southern. Ozone was being depleted in the Arctic as well, by as much as 15 to 17 percent at some altitudes. Over the heavily populated mid-latitudes of the globe, the researchers believe, winter ozone levels may have dropped in the past decade by as much as 4 to 6 percent. And even if all CFC production worldwide were to be halted-an unlikely possibility even to the signers of the Montreal Protocol-the amount already existing and waiting to be released to the atmosphere would mean a continuing ozone drop for decades to come. THE WORRY IS that stratospheric ozone forms the earth's principal shield against dangerous ultraviolet radiation from the sun. This short wavelength light, below the range of human visibility, kills many forms of life bacteria, for example, which is why it is used for steril izing surgical instruments and protecting many foods. But ultraviolet also kills beneficial forms of life, and it can affect the life cycle of many plants, both on land and in the seas. Middle and long wavelengths of UV cause not just tanning and extreme sunburn in human skin but the most prevalent forms of skin cancer. They also can cause cataracts in the eyes and injure the immune responses of skin, which protect us from many harmful, even deadly diseases. The Environmental Protection Agency issued a risk assess ment in 1987, predicting that for every one percent drop in global ozone, there would be a one to three percent increase in skin cancers. Global ozone has dropped at least 2 percent in the past ten years, EPA said, leading to possibly four million added cases of skin cancer. In the past ten years alone, dangerous skin Is Our World Warming?