National Geographic : 1990 Oct
On the road to understanding sources of methane, scientists from the National Center for Atmospheric Research in Boul der, Colorado, test what turned out to be an innocent suspect fresh asphalt (above). Wide ranging research suggests that leaks and venting from coal, oil, and naturalgas production may be underestimated. Cattle, a known source of methane, are increasing world wide-faster than the human population. The same bacteria that enable a cow to turn grass into meat or milk cause it to expel methane, roughly 14 cubic feet a day. to the drying of soil in summer. Destructive droughts, such as that of 1988 in North America, would strike more often, until the Great Plains and Ukraine turn semidesert. Storms such as hurricanes and tornadoes might become more violent. Forests would decline and change under the temperature rise, and wild life would have to migrate-if it could-or perish. The perma frost under Arctic tundra would thaw, deep peatlands would decompose, and vast new amounts of carbon dioxide and meth ane could be released. And just as inevitably, as ocean waters warm and expand and the ice on Greenland and Antarctica melts back, the seas would creep higher onto the edges of the continents. Large parts of such low countries as Bangladesh-already swept by ruinous floods and typhoons-would be submerged; cities like Miami, Venice, even New York, would cower behind dikes. "If a rise of one to three feet, as the models have predicted, seems extreme," says environmental scientist Stephen Leather man of the University of Maryland, "keep in mind that the oceans rose more than 300 feet after the last ice age-all in only a few thousand years." If the ice cap on the island of Greenland were to melt com pletely, glaciologists estimate the oceans would rise another 20 feet. Sea level in the eastern United States has already risen a foot in this century alone, and it is predicted to go up at least another foot in the century ahead. With that one-foot rise, Leatherman says, the high-water line at Ocean City, Maryland, will move inland 100 to 200 feet; in Florida, 200 to 1,000 feet; in Louisiana, several miles. Yet paradoxically, say other glaciologists, the huge ice domes on both Greenland and Antarctica may not be shrinking but growing. The paradox is that this too may be a sign of global warming. As the atmosphere warms, it holds more water vapor from evaporation of oceans and soil; hence more snow falls in the polar regions, hence more ice and possibly lower sea levels. But the warmer seas eventually will melt back the fringes of the polar ice, and the oceans will creep inexorably higher. VORETELLING WHAT MAY HAPPEN to the world if it should warm by even one or two degrees is the tough est problem facing climatologists today. Even though there have been times in the dim geologic past when temperatures were warmer-with no ice at all on the polar regions-there are vast differences today. No one knows whether the "wild card" of human activity will dis rupt or make more extreme the cycles ordained by nature. To try to predict the effects of human intervention, scientists mathematically simulate the weather systems of the globe. Their equations, called general circulation models (GCMs), are so com plex that only a few of today's supercomputers can solve them. The equations relate such things as the balance of radiation to and from the planet, air circulation, evaporation and rainfall, ice cover, sea-surface temperature-then try to assess what might happen if the sun were to become brighter by a tiny amount or if the carbon dioxide in the atmosphere gradually doubles as expected. The computers then calculate and map the changes in Is Our World Warming?