More than 9,500 researchers from dozens of scientific fields convened last month for the fall meeting of the American Geophysical Society, held annually in San Francisco. Although NASA’s Mars missions grabbed plenty of attention, some of the most compelling reports came from other areas of research. Among the highlights:
Dusting Off the Future: Given current trends, the amount of carbon dioxide in the atmosphere will surely continue to rise over the next century. One important but previously overlooked consequence of all that CO2 may be less dust in the air, says Natalie Mahowald of the National Center for Atmospheric Research in Boulder, Colorado. She and her colleagues ran a computer simulation estimating the amount of dust in the atmosphere under a variety of different scenarios. The simulation revealed that high carbon dioxide levels, matching those predicted for the next 100 years, would reduce winds and increase moisture and vegetation. As a result, from 20 percent to 63 percent less dust would be churned off desert floors and up into the atmosphere. “For people living in dusty regions—North Africa, for example—it would definitely be a good thing, since the amount of dust really affects their life negatively. Even the southeastern United States has days when the air quality violates EPA standards due to dust from North Africa,” Mahowald says.
Other effects are far less desirable. Dust reflects sunlight, so with less dust in the atmosphere to bounce the sun’s rays away, surface temperatures will rise. (The researchers do not yet know by how much.) Also, dust that blows into the oceans provides iron, a vital nutrient, to marine organisms. “If you reduce iron deposition, you may well reduce ocean productivity and reduce the uptake of carbon dioxide by the oceans. This would cause even more CO2 to accumulate in the atmosphere, making our global warming problems worse,” Mahowald says.
Listen to the Lightning: Bruce Gungle has hit on an easy and accurate way to predict the amount of rain in a thunderstorm: Count the number of associated lightning bolts. While Gungle was a graduate student with the University of Arizona’s department of atmospheric science, he and his colleague, atmospheric scientist E. Philip Krider, measured rainfall and tallied the cloud-to-ground lightning strikes during nine thunderstorms in a 225-square-mile area around the Kennedy Space Center and Cape Canaveral in Florida. Each lightning strike was associated with 4 million gallons of rain, on average. The mechanism underlying the relationship is basic physics, says Gungle, now a hydrologist with the U.S. Geological Survey’s Water Resources Discipline in Tucson, Arizona: “The charge separation in a thundercloud that leads to lightning is the result of the interaction of the supercooled water and ice particles in the cloud. Because the precipitation in a thundercloud is responsible for the generation of the lightning, it follows that there will be a quantifiable relationship between the two.”
By tracking lightning strikes, researchers could produce real-time rainfall predictions, even though the actual amount of rainfall associated with strikes varies from region to region. “Once a lightning-rainfall relationship has been established for a region, on any given thunderstorm day you simply have to determine the cloud-to-ground lightning rate, or total, and enter that number into an equation to get a reasonable prediction of the rate or total amount of rain the thunderstorm is producing,” Gungle says.
Scorching the Silk Road: For centuries, the 4,000-mile-long Silk Road provided a vital connection between China and the West for trade and the exchange of ideas. Ancient civilizations arose and thrived in oases along the route, which traced along the Great Wall of China, climbed through the Pamir mountains, then ran across Afghanistan and west into the Levant. By the ninth century A.D., however, most of the inner-Asian cities along the Silk Road had been abandoned. Geologist Kuo-Yen Wei of National Taiwan University says the cities disappeared not because of the diminished trade that resulted from conflicts among Tibetans, Chinese, Arabs, and other local populations, as commonly thought, but because of a drastic climate change that turned formerly lush oases into hot, dry desert.
The idea that climate change could have affected the ancient Asian civilizations was suggested nearly a century ago, but “the theory seems to have been forgotten,” says Wei, who has bolstered the idea with modern evidence. He and his colleagues pulled sediment cores covering the past 5,000 years of climate history from China’s Lake Bosten, located in the northwest region of Xinjiang Uygur. They measured two forms of the carbon atom—common carbon-12 and its heavier and rarer cousin, carbon-13. These isotopes are known to vary in abundance in lake deposits depending on whether the local vegetation is adapted to wet or dry conditions. The cores revealed that the climate was stable—and humid—from the second century B.C. to about the eighth century A.D. but then suddenly dried up, perhaps in as few as 40 years. “The response of the human society to this drastic aridification took several decades. Basically, these oases civilizations struggled, migrated, and eventually vanished from the deserted desert,” Wei says.
The burgeoning desert may also have affected the expansion of the Islamic faith through inner Asia, Wei says. A millennium earlier, Buddhist ideas had traveled rapidly from India north and east into China, via the Silk Road. In inner-Asian communities, the religion was eventually displaced by Islam, but only gradually. “Dunhuang, where many famous caves with Buddhist paintings were found, were spared from the iconoclastic Muslims. I think the wide, arid desert might have provided a natural protection. In other words, the aridification in the last millennium in inner Asia made it hard for the spread of Islam, in contrast to the quick spread of Buddhism when the oases enjoyed better water supplies from the glaciers of the Tian mountains to the north and the Kunlun mountains to the south,” Wei says.
Fungus Down Under: A German geomicrobiologist has found fossil fungi buried below more than 150 feet of volcanic rock and under more than a mile of North Pacific water, hinting that life can persist in the most improbable locations. Gabriela Schumann of the University of Gˆttingen in Germany discovered distinctively funguslike filaments inside bubbles in a 46-million-year old basaltic lava flow, recovered during Leg 200 of the international Ocean Drilling Project. Although the fungi are dead, Schumann suspects that similar living forms may still exist deep below the oceans, where the earliest life on Earth may also have originated. “I believe that under the appropriate conditions fungi could live within deep-sea sediments and even within basalts,” she says.
Previously, only simple single-celled microbes had been found in deep ocean rocks. Fungi, however, are multicellular, relatively complex organisms—perhaps the first of many that will be found in this environment, Schumann says: “We believe this is further evidence for the impressive diversity and versatility of life in the deep biosphere. We should expect to find many more known and unknown organisms forming complex populations in this important habitat.”
