No Global Warming?; February 1994; Scientific American Magazine; by Leutwyler; 1 Page(s)

Since 1958, when researchers first began to measure the rate at which carbon dioxide accumulates in the atmosphere, they have seen a consistent increase, perturbed only by minor seasonal fluctuations. Then, about four years ago, the trend began to waver. First a decline set in, followed by a plateau. After that, the decline resumed--sharply. The event has left scientists, including those at the observatory on Mauna Loa in Hawaii, established by the late Harry Wexler to make the measurements, wondering what has happened.

Adding to the confusion, says Charles D. Keeling of the University of California at San Diego, who has operated a gas analyzer at the observatory since its founding, is the fact that accumulation started to slump while the atmosphere was in the throes of an El Nino, a periodic shift in the circulation of trade winds over the Pacific that affects global weather and ocean currents. During an El Nino, such as those of 1982-83 and 1986¿87, atmospheric carbon dioxide levels tend to rise faster than they do at other times. Keeling suspects that plants and soils release more carbon dioxide during an El Nino because when an Asian monsoon collapses, it causes drought conditions. Whatever has been reducing contributions of carbon dioxide to the atmosphere had such an impact that it entirely overrode the effects of an El Nino.