February 28, 2007
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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
OF GENERAL INTEREST
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
Earths 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.
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; email@example.com), 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.
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 Earths wobble around its axis, which would
have an interannual effect on the distribution of solar radiation on the
surface of the Earth.
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
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
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.
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