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Science Briefing

Just in time for the next El Nino event, which some forecasts are pegging to begin toward year's end, a new lay-oriented book about the phenomenon will appear on bookshelves. Mickey Glantz (ESIG director) is the author of Currents of Change: El Nino's Impact on Climate and Society, released this month by Cambridge University Press.

Mickey's new book aims to explain to a broad audience what El Nino is, how its effects might be forecast, and its far-reaching impacts on society at large. Sections cover the emerging interest in El Nino, the character of various El Nino episodes (including what Mickey calls the "anomalous anomaly" of 1982-83), and the motives for studying El Nino. The book includes short statements from 35 researchers on how they view the phenomenon. It will appear in both hardback and paperback editions.

The book is dedicated to the late Dana Thompson, a fellow NCAR postdoctoral student with Mickey in 1974. "He came from the world of physical science," writes Mickey, "and I came from the world of social science. Dana introduced me to the El Nino phenomenon, and for several years we joined efforts to address the physical and societal aspects of this important recurring natural process. Over the years, Dana was not only my partner in this endeavor but my mentor as well."

Mickey Glantz
Mickey's popular writings include "Environmental Minute," a weekly column published in the Boulder Daily Camera and distributed by Knight-Ridder to newspapers nationwide. He has written or coauthored over 100 scholarly papers and written more than 15 books, including Drought Follows the Plow? (Cambridge, 1994), Teleconnections Linking Worldwide Climate Anomalies (Cambridge, 1991) and Forecasting by Analogy (Westview, 1987). Mickey has headed ESIG since 1979.

Over the past several decades, average global temperatures in the lower stratosphere have dropped to historic lows, even as readings near ground level have risen. The surface rises have been attributed largely to increases in greenhouse gases. At the same time, scientists have suspected that the stratospheric drops were related to depletion of ozone (a greenhouse gas and a strong absorber of ultraviolet light). Now a study coauthored by ACD's Bill Randel has confirmed that ozone depletion and high-level cooling coincide in time and space. The study, written by V. (Ram) Ramaswamy and Dan Schwarzkopf (both of NOAA Geophysical Fluid Dynamics Laboratory) and Bill, appears in the 15 August issue of Nature.

Bill Randel
The authors fed satellite-derived monthly ozone losses by latitude into a GFDL global computer model that extends to a height of 80 kilometers. Since the losses were not specified by height, the authors constructed a seven-kilometer-deep profile of depletion extending upward from the troposphere/stratosphere boundary, which varies from 17 km at the equator to 9 km at the poles. This approximates the vertical profile of ozone loss derived from balloon measurements.

For the period 1979-90, the GFDL model results showed temperature drops through most of the lower stratosphere. When compared to satellite-based temperature observations, the model-produced pattern of cooling by latitude and month of year correlated well, serving as a fingerprint of ozone-induced cooling. The model's cooling was most intense at high latitudes during each hemisphere's spring, as expected. But cooling appeared even above the tropics, where little ozone loss had occurred. Bill and colleagues attribute this to circulation changes induced by the ozone losses at higher latitudes.

Along with ozone, changes in the concentration of other greenhouse gases also could influence stratospheric temperatures. The authors compared the relative impacts of these gases using a separate model. They found that ozone's effect predominated over estimated long-term trends (some extending back to 1765) in carbon dioxide, methane, nitrogen oxide, and chlorofluorocarbons: "The computed 1979-90 ozone effect on lower-stratospheric temperature outweighs the effect of changes in other gases, not only over the past 10-30 years but also over the past two centuries."

Bill and colleagues are now working on a more detailed assessment of the temperature trends, including their vertical structure and the impact of volcanic and solar influences. "Overall," says Bill, "the stratosphere is less complicated than the troposphere in its interannual variability. This suggests that evidence of climate change might be easier to observe in the stratosphere. The thermal effects of ozone depletion are an important component in deciphering the space-time structure of climate change."

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Prepared by Jacque Marshall, jacque@ucar.edu, 303-497-8616