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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 8, AUGUST 1998

PROFESSIONAL PUBLICATIONS...
OF GENERAL INTEREST

Item #d98aug1

“Effects of Orbital Decay on Satellite-Derived Lower-Tropospheric Temperature Records,” F. J. Wentz (Remote Sensing Systems, 438 First St., St. 200, Santa Rosa, CA, 95401), Matthias Schabel,Nature 394, 661-664 (Aug. 13, 1998).

Microwave sounding units have been used on satellites since 1979 to determine the atmospheric temperature at an altitude of about 3.5 km. These measurements have exhibited a cooling of the atmosphere of ¾0.05 K per decade. At the same time, temperature measurements taken at the Earth’s surface have shown an increase of about 0.13 K per decade during the same period. Although the temperature being measured by the satellites is not the same as the temperature that is measured at the surface of the Earth, the difference between these two measurements has raised questions. Reexamination of the data and data-handling methods revealed that orbital decay of the satellites was not factored into the analyses. Recalculation of the observed temperatures that included a representation of orbital-decay effects indicated an increase of 0.07 K per decade in overall global temperature between 1979 and 1995.

Item #d98aug2

“Changes in the Number of Lightning Deaths in the United States During the Twentieth Century,” R. E. Lopez (National Severe Storms Lab., NOAA, 1313 Halley Cr., Norman, OK 73069; lopez@nssl.noaa.gov), R. L. Holle,J. Climate 11 (8), 2070-2077 (1998).

The number of lightning deaths in the contiguous United States for each year from 1900 to 1991 were population normalized and plotted vs. year, revealing an exponential decrease in the number of deaths per million people per year. This trend tracks the similarly exponential decrease in the rural population of the country for the same period, suggesting that the decrease in lightning deaths resulted largely from the change from a rural population to an urban one. The occurrence of lightning deaths was also compared to thunder-day statistics and average surface-temperature values, and a parallelism was noted, indicating that the lightning-death rates were climatically driven.

Item #d98aug3

“Interannual Polar Motion with Relation to the North Atlantic Oscillation,” Yonghong Zhou (Shanghai Observatory, Chinese Acad. Sci., Shanghai 200030, PRC), Dawei Zheng, Ming Zhao, B. F. Chao,Global and Planetary Change 18, 79-84 (1998).

The North Atlantic Ocean exhibits an oscillation in the atmosphere and ocean similar to the Southern Oscillation of the Pacific Ocean. But the oscillation in the North Atlantic is north-south, meaning that the mass of water that is displaced interannually has a different radius of rotation around the Earth at the end of its travel than it had at the beginning. As a result, this shift of mass changes the center of gravity of the planet, the axis of its rotation, and thus the nominal location of the poles. Monthly data on the polar motion were compared with monthly values for the North Atlantic Oscillation Index (a measure of the intensity of that phenomenon) with time-domain cross-correlation and with frequency-domain coherence. A significant correlation was observed between the two series, suggesting a possible contribution of the North Atlantic Oscillation to the polar motion and the Earth’s wobble around its axis, which would have an interannual effect on the distribution of solar radiation on the surface of the Earth.

Item #d98aug4

“On the Scattering Greenhouse Effect of CO₂ Ice Clouds,” R. T. Pierrehumbert (Dept. Geophys. Sci., Univ. Chicago, Chicago, IL), C. Erlick,J. Atmos. Sci. 55 (10), 1897-1903 (1998).

When idealized, CO₂ ice clouds reflect thermal infrared radiation but do not absorb or emit it. Such clouds would allow the Earth to perform a cold start and recover from a global glaciation. A simple cloud optical model was used to estimate the planetary radiation budget as affected by such clouds, and the results indicate that the greenhouse effect produced by the clouds would cancel out most of the cooling effect produced by the clouds’ albedo. In fact, the greenhouse effects may lead to a net warming when compared with the case with no CO₂ ice clouds.

Item #d98aug5

“Changes in Soil Carbon Following Afforestation in Hawaii,” M. A. Bashkin (Dept. Forest Sci., Colo. State Univ., Fort Collins, CO, 80523), Dan Binkley,Ecology 29 (3), 828-833 (1998).

Sugarcane fields were afforested with Eucalyptus saligna, a fast-growing species, and the subsequent changes in soil carbon were measured with isotopic techniques. Carbon was gained from the new trees and lost from the carbon store deposited by the prior cane cultivation. The 11.5 Mg/ha gained in the top 10 cm of soil in the Eucalyptus stand was offset by the 10.1 Mg/ha lost from the 10- to 55-cm cane-deposited layer.

Item #d98aug6

“Does Atmospheric CO₂ Police the Rate of Chemical Weathering?” W. S. Broecker (Lamont-Doherty Earth Obs., Columbia Univ., Palisades, NY, 10964), Abhijit Sanyal,Global Biogeochemical Cycles 12 (3), 403-408 (1998).

Over the millennia, the Earth has seen great variations in the rate at which CO₂ is vented from its interior and in the rate that the continental rocks have been chemically weathered. The inputs of CO₂ and CaO to the oceans, therefore, have seesawed back and forth. As a result, the CO₂ concentration in the atmosphere must have swung wildly in one direction and then the other. Some feedback mechanism must occur to keep the Earth from overheating and killing animal life at one extreme or overchilling and killing plant life at the other; it has, in fact, steered a careful course between these two extremes. In 1983, Walker et al. proposed that the feedback mechanism that balances CO₂ availability and CaO supply is the chemical weathering of silicates by atmospheric CO₂. Many researchers have opposed that proposal, but Broecker and Sanyal feel the choice of CO₂ weathering is “obvious” because no other mechanism presents itself.