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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 11, NUMBER 12, DECEMBER 1998

PROFESSIONAL PUBLICATIONS...
OF GENERAL INTEREST

Item #d98dec1

“Anthropogenic Influence on the Autocorrelation Structure of Hemispheric-Mean Temperatures,” T. M. L. Wigley, R. L. Smith, and B. D. Santer,Science 282, 1676 (Nov. 27, 1998).

Global temperature data were analyzed by determining the average temperature in the northern hemisphere and that in the southern for each of 115 years. The effects of volcanoes and of variations in solar activity were factored into the data. The resultant values were then compared with similar measurements taken up to 20 years earlier or later to see if there was any correlation. Random variation in temperature would produce little or no correlation, but the correlation factors indicated that the data were following decisive trends. Parallel analyses were carried out with the output from computer models of global temperature, which models had been set to ignore the radiative effects of greenhouse gases. When the correlations of the model data were compared with the correlations of the observed data, the calculations indicated that the Earth would have to be about six times as sensitive to the sun’s effects than it is in order for the sun to produce the observed global warming. Incorporating the effects of greenhouse gases into the models produced correlations comparable to those for the global warming that has been observed. The effects of volcanic eruptions were found to be too infrequent and short-lived to affect the long-term trends. The results indicated that variations in solar output could affect some long-term trends but that solar forcing alone could not explain the observed variations in global temperature. The results strengthened the contention that humans have had a discernible human influence on global climate and implied that the computer models of climate change are realistic.

Item #d98dec2

“Climate Forcings in the Industrial Era,” J. E. Hanson et al.,Proc. Natl. Acad. Sci. USA 95, 12753-12758 (1998).

Atmospheric greenhouse gases can be measured very accurately, and a historical record has been amassed that covers decades of direct observations and millennia of proxy data. These gases indisputably cause a positive (warming) forcing on the atmosphere. But other forcings, such as aerosols, clouds, and land-use and land-cover patterns, are not so well characterized. As a result, insufficient information is available at this time to predict long-term climate changes. As a result, the predominant issue in climate projections is no longer climate sensitivity but climate forcings.

Item #d98dec3

“Evidence for Extreme Climatic Warmth from Late Cretaceous Arctic Vertebrates,” J. A. Tarduno et al.,Science 282, 2241-2244 (Dec. 18, 1998).

The fossilized remains of a champsosaur, a crocodilian reptile, and other species that date to 92 to 86 Ma BP were found on Axel Heiberg Island in the high Canadian Arctic. Other warm-climate species (both plants and animals) had been detected in the far north before, but this is the first ectotherm found at this latitude. Because modern ectotherm populations die off at a temperature of about 5° C, this discovery indicates that the climate in the Late Cretaceous at that latitude was likely 14 to 35° C. High rates of volcanism at that time produced concentrations of atmospheric CO₂ many times today’s concentration, and the resulting greenhouse effect is suspected of producing the higher temperatures indicated by the fossil record.

Item #d98dec4

“Increased Summertime Heat Stress in the U.S.,” D. J. Gaffen and R. J. Ross,Nature 396, 529-530 (1998).

A threshold of ambient temperature and humidity has previously been identified above which mortality from heat- related sickness increases sharply. Investigation of the U.S. weather records at 113 stations identified extreme-heat events (heat waves) between 1949 and 1995 that exceeded the threshold and that were narrowly defined in time and location. During the period studied, the annual number of days that exceeded the mortality threshold increased 67%, the number of nights that exceeded the threshold climbed 78%, and the number of heat waves each year increased 88%. Urbanization may have affected these trends, but the regional consistency of the data suggests that such local influences are minimal.

Item #d98dec5

“2000 Years of Drought Variability in the Central United States,” C. A. Woodhouse and J. T. Overpeck,Bull. Am. Met. Soc. 79 (12), 2693–2714.

The existing paleoclimatic literature (derived from historical documents; tree rings; archaeological remains; and sediments piled up by lakes, rivers, and winds) was reviewed to determine the drought record for the Central United States. Droughts of the 20th century were found to be only moderately severe and relatively short in comparison with droughts that occurred much longer ago. Indeed, from a historical perspective, the 1930s Dust Bowl and the l950s drought were not unusual events and might recur once or twice a century. Evidence was also found of two “megadroughts,” one in the last quarter of the 13th century and one in the second half of the 16th century that covered the entire western United States. Such megadroughts could happen again, just through natural variability; land-use practices in the Great Plains and global warming could enhance the possibility.

Item #d98dec6

“Effect of Interannual Climate Variability on Carbon Storage in Amazonian Ecosystems,” Hanqin Tian et al., Nature 396, 664-667 (1998).

The Amazon forests are responsible for about 10% of the Earth’s terrestrial primary productivity and thus are important sinks for the atmosphere’s carbon. But they experience large variations in CO₂ uptake from year to year because of El Niño. A biogeochemical computer model was used to investigate how these ecosystems respond to the influences of El Niño. It showed that El Niños produce hot, dry weather that limits Amazonian productivity and turns the forests there into net sources of CO₂. In other years, the forests act as a sink for CO₂. The variations in these fluxes are large, and soil moisture, which affects both plant and soil processes that entail CO₂, appears to play an important role in determining the magnitudes of these flux variations.

Item #d98dec7

“Hsp90 as a Capacitor for Morphological Evolution,” Suzanne Rutherford and Susan Lindquist,Nature 396, 336-342 (1998).

Studies of fruit-fly genetics revealed that heat-shock proteins (specifically, Hsp90) protect other proteins against high temperatures and help them perform properly. Hsp90 does this within a narrow range of temperature, around 25° C. However, reserves of Hsp90 can be overwhelmed by extreme heat shocks and other stresses. When that happens, mutant proteins involving multiple genes can be revealed in large numbers of genetically determined physical traits. Often, these physical-trait alterations are harmful to the individual organism, but occasionally they are beneficial and sometimes allow the organism to successfully cope with the stressor that caused the mutation. This process, then, can be viewed as a mechanism for increasing genetic diversity upon which natural selection can act to respond to and cope with a stress imposed on the species.