National Geographic : 1990 Oct
Geophysical FluidDynamics Lab (left), Stephen Schneider of the National Center for Atmo spheric Research (left, below), and James Hansen (bottom) of NASA's Goddard Institute for Space Studies. Might not the sun's 11-year sunspot cycle or irregularities in solar output directly affect earth's climate? It is an intrigu ing but unanswered question for astrophysicists like John Eddy (below), director of the Office for Interdisciplinary Earth Studies in Boulder. decomposing tundra and marshes, rice fields, termites, and the guts of cattle, is increasing in the atmosphere faster than CO2, at something like one percent a year. And molecule for molecule it has 20 to 30 times the greenhouse effect of CO 2 . Nitrogen gases, from fertilizers as well as car exhausts and factory smokestacks, chlorofluorocarbons (CFCs) and other industrial products-all the other gases we're pouring into the air-are already doubling the warming potential of CO 2 alone. "We can hope to reduce some of them, such as the CFCs that attack stratospheric ozone," he said. "But the others go with the industrial development of the world; all we can realistically hope is to slow their release, to gain time to cope with the results. "If we can delay a 2°C increase of global temperature from 2025 to 2050, we will have more time to develop alternate energy sources: Nuclear-possibly fusion-is one option, despite its problems. But tapping the sun directly, by solar heat plants and converting sunlight directly into electricity, is both possible and coming down in cost." I was to see his future in California, at the Rancho Seco nuclear plant outside Sacramento, flanked by 20 acres of solar panels slowly swinging with the sun across the sky; at a pioneer ing solar-cell factory near Los Angeles, where a breakthrough in "thin-film" technology was closing in on conventional electric power costs; and on a treeless mountain pass above Oakland, where a seemingly endless array of propellers taps the sun's energy from the winds sweeping in off the Pacific (pages 92-3). C OMPUTER FORECASTING of climate is uncertain for rea sons other than the sheer complexity of the equations. There are variables and feedbacks that even the best of the models barely approach. The oceans are the chief reservoir of heat, controlling weather over the entire globe. As currents such as the Gulf Stream carry the heat from the tropics to high latitudes, cold water from the polar regions sinks and flows toward the Equator, overturning the seas about every thousand years. "The tropical oceans are the driving mechanism of the cli mate," says climatologist Eric J. Barron of Pennsylvania State University. "The oceans are the memory of the climate system," adds Kirk Bryan of GFDL at Princeton. Yet until recently even the most advanced mathematical models treated the oceans only as vast, shallow swamps. Carbon dioxide is absorbed by seawater, some of it incorpo rated into the shells of tiny marine creatures that die and become carbonate sediments on the bottom. Scientists estimate that a significant part of the seven billion metric tons of carbon released into the air each year is taken up in the seas. Oddly, the colder the water, the more CO 2 it can hold. As the oceans warm under the effect of more CO 2 in the atmosphere, there is great uncertainty about how much of that new CO 2 will be absorbed. Is there a limit to how much carbon can be locked away? Have the oceans already reached their holding capacity? World-famed geochemist Wallace S. Broecker of Columbia University's Lamont-Doherty Geological Observatory worries that rapid switches in ocean circulation might occur under Is Our World Warming?