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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 12, NUMBER 4, APRIL 1999

JOURNAL ARTICLES...EL NIÑO

Item #d99apr20

“Genesis and Evolution of the 1997-98 El Niño,” M. J. McPhaden,Science 283 (5404), 950-954 (1999).

Data from satellites and a network of buoys moored near the equator indicated a build-up of excess heat in the western Pacific in 1995 and 1996. The onset of the El Niño was triggered by weather systems migrating into the western Pacific from the Indian Ocean in late 1996. In early 1997, a weakening and reversal of the trade winds in the equatorial Pacific rapidly led to unusually warm sea-surface waters. With the collapse of the easterly trade winds, warm surface waters migrated eastward from the western Pacific. In early 1998, the high sea-surface temperatures added to the usual seasonal warming. When the trade winds abruptly returned to near normal strength in the eastern Pacific in May 1998, the cold subsurface waters were drawn upwards, and sea-surface temperatures plummeted, marking an end to the El Niño. The study also suggests that natural decadal fluctuations in ocean conditions may have combined with global warming to influence the 1997-98 El Niño.

Item #d99apr21

“Horse Sickness and ENSO in South Africa,” M. Baylis, P. S. Mellor, and R. Meiswinkle,Nature 397, 574 (1999).

Meteorological patterns and records about epidemics of African horse sickness back to 1803 were analyzed, and 13 of the 14 outbreaks of African horse sickness coincided with an El Niño. A spell of drought followed by heavy rainfall, climatological results associated with El Niño, seems to alter the breeding sites and to increase the population of the biting midge, the insect that spreads the disease. These results imply that the increasing frequency of El Niño currently observed could result in an increase in a range of diseases spread by flying insects, including diseases that affect humans.

Item #d99apr22

“El Niño and Global Warming,” K. E. Trenberth,Current: The Journal of Marine Education 15, 12-18 (1998).

El Niños transfer heat from the Pacific Ocean to the atmosphere, and the global mean temperature peaks three to four months after an El Niño peaks. This warming helps dry out regions in Indonesia, Australia, Africa, and South America already prone to drought. Analysis indicates that a departure by one standard deviation in the Southern Oscillation Index results in a warming of the global atmosphere of about 0.1° C. The theory is put forth that much of the heat trapped by the greenhouse effect may be going into the oceans and later released through such mechanisms as El Niño, producing El Niños that are larger and more frequent.