Ozone Depletion Also Affects Atmospheric Meth- recent research indicates a reduced rate of increase. ane Trends In agreement with the recently measured trends, Over the last decade, scientists have discovered Madronich and Granier estimate that the increase in significant reductions in total atmospheric ozone be- U V should lead to a reduction of the methane increase lieved to be caused by human-produced chlorofluoro- from about one percent per year to about 0.6% per carbons (CFCs) and bromines. Recently, Sasha year. For more information, contact Joan Frisch at Madronich and Claire Granier, atmospheric chemists (303) 497-8607. at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, have determined that NOAA to Investigate Arctic Methane Plumes ozone depletion may have changed the lifetime of The National Oceanic and Atmospheric Adminis- another atmospheric gas, methane. A paper outlining tration (NOAA) next month will attempt to confirm that their research is published in the 3 March issue of massive atmospheric plumes periodically observed Geophysical Research Letters (GRL). rising out of ice in the east Siberian Sea during the past The continuing loss of protective ozone allows 15 years contain methane gas escaping from the seafloor. greater amounts of ultraviolet (UV) radiation to reach A United States scientist flying in a Russian AN-2 the earth's surface. Besides its harmful effects on research aircraft will attempt to collect air samples humans, animals, and plants, increased UV radiation from one of the plumes breaking through sea ice affects certain chemical reactions in the lower atmo- surrounding Bennett Island. The island is several sphere. Madronich and Granier have found that be- hundred miles north of the Siberian coastline in an cause of stratospheric ozone loss, significantly more area previously closed to all but Soviet military and UV radiation (especially UV with wavelengths less scientific personnel. than 330 nanometers or billionths of a meter) is During most of the last several million years, scien- reaching the troposphere, where it is responsible for tists believe that the Bennett Island area was part of a the photochemical destruction of tropospheric ozone. coastal plain inhabited by mammoths and other verte- The destruction of tropospheric ozone, in turn, results brates. Thick permafrost and associated methane in the formation of excited atomic oxygen, which is the hydrates are believed to have formed over the area chemical precursor of highly reactive hydroxyl (OH) that is now covered by waters of the Siberian Sea. radicals. OH radicals take part in chemical reactions Based on geological information, historical records, that influence the lifetimes of many tropospheric gases, satellite analyses, and knowledge of hydrocarbon including some greenhouse gases. Madronich and reservoirs, scientists have concluded that the plumes Granier believe that the OH increases due to strato- are the result of melting and vaporizing of the methane spheric ozone depletion are partly responsible for hydrates, possibly caused by warming of the Arctic. shortening the lifetime of tropospheric methane. The released methane, a greenhouse gas, could be Methane is a greenhouse gas produced both natu- adding to atmospheric warming, suggested Russell rally and anthropogenically. Termites, wetlands, and Schnell of NOAA's Climate Monitoring and Diagnos- melting tundra are major sources of naturally occur- tics Laboratory in Boulder, Colorado. ring methane. Most human-produced methane comes To confirm speculation on the plume's chemical from cattle and other ruminants, rice paddies, munici- makeup, Anthony Hansen of the University of pal landfills, and the burning of fossil fuels and bio- California's Lawrence Berkeley Laboratory, a frequent mass. Like carbon dioxide (C0 ), methane is a con- collaborator with Schnell in NOAA Arctic studies, will tributor to global warming, but is much more effective. fly a series of plume reconnaissance flights over It takes 25 molecules of C0 to match the warming Bennett Island. effect of a single molecule of methane. Therefore, "Given the statistics from previous observations, relatively small increases in atmospheric methane there is a better than 50 percent chance that a plume could trigger substantial increases in global warming. will break through the ice and be intercepted by our Past measurements of methane reveal a steady sampling," Schnell said. increase (around one percent per year), generally Air samples collected during any interception will be believed to be the result of increased human activity. analyzed for chemical composition at NOAA's Boulder Methane levels are still rising, along with concerns laboratory. For more information, contact William about its growing contribution to global warming, but Brennan at (303) 497-6286. • Bulletin American Meteorological Society
Bulletin of the American Meteorological Society – American Meteorological Society
Published: May 1, 1992
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