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 7, JULY 1998
CLOUDS, AEROSOLS AND CLIMATE
"Uncertainties of Aerosol Effects in Global Climate Models,"
J.S. Gaffney (Argonne Natl. Lab., 9700 S. Cass Ave., Argonne IL 60439),
N.A. Marley,Atmos. Environ., 32(16), 2873-2874, Aug. 1998.
This commentary emphasizes the urgency of including the various effects
of aerosols in climate models, which will require better measurements of
aerosol chemical compositions and radiative properties as a function of
size, in addition to temporal and spatial aerosol distributions.
"Intercomparison of Models Representing Direct Shortwave Radiative
Forcing by Sulfate Aerosols," O. Boucher (Lab. d'Optique Atmos.,
Univ. de Lille-I, 59655 Villeneuve d'Ascq Cedex, France; e-mail:
email@example.com), S.E. Schwartz et al.,J. Geophys. Res.,
103(D14), 16,979-16,998, July 27, 1998.
The comparison involved 12 groups using 15 models to examine radiative
forcing by sulfate aerosol for a wide range of particle radius, aerosol
optical depth, surface albedo, and solar zenith angle. All models
simulated forcings of comparable amplitude and exhibit a similar
dependence on input parameters.
"Subsonic Aircraft: Contrail and Cloud Effects Special Study
(SUCCESS)," O.B. Toon (LASP, Univ. Colorado, Boulder CO 80309), R.C.
Miake-Lye,Geophys. Res. Lett., 25(8), 1109-1112, Apr. 15,
Overviews results of a multi-aircraft field campaign held in 1996,
presented in detail in a special section of this issue (and to be
continued in future issues).
"Global Average Climate Forcing and Temperature Response Since 1750,"
P.R. Rowntree (25 Bramblegate, Crowthorne, Berkshire RG45 6JA, UK),Intl.
J. Climatology, 18(4), 355-377, Mar. 30, 1998.
Estimates major radiative forcing factors in climate change for the
period since 1750. Fossil fuel burning had a minor role until the
mid-twentieth century, with the relatively small effects of fossil fuel CO2
being cancelled by sulfate aerosols from the same source. Shows that a
simple box-diffusion model simulates many features of the climate record,
without including either variations in solar intensity or internal
variability, but the simulation does include volcanic aerosols, which most
studies have neglected.
"Clouds, Contrails and Climate," J.H. Seinfeld (Chem. Engin.
(104-44), Calif. Inst. Technol., Pasadena CA 91125; e-mail:
firstname.lastname@example.org),Nature, 391(6670), 837-838, Feb.
The formation of cirrus clouds, which warm the Earth, is incompletely
understood, but recent studies hint that they can evolve from jet
contrails. This is an unsuspected but possibly important effect of human
activity on climate, offering a new way to study the processes involved.
"Effect of Black Carbon and Sulfate Aerosols on the Global Radiation
Budget," I. Schult, J. Feichter (M. Planck Inst. Meteor., Bundestr.
55, D-20146 Hamburg, Ger.; e-mail: email@example.com), W.F. Cooke,J.
Geophys. Res., 102(D25), 30,107-30,117, Dec. 27, 1997.
Calculations based on global distributions show that the presence of
black carbon, the main absorbing component of anthropogenic aerosol, may
reduce the cooling effect of aerosol, thus leading to an increase in
"Supercooled Cirrus Cloud Formation Modified by Nitric Acid Pollution
of the Upper Troposphere," A. Laaksonen (Dept. Physics, POB 9, 00014
Univ. Helsinki, Finland; e-mail: firstname.lastname@example.org), J. Hienola,
M. Kulmala,Geophys. Res. Lett., 24(23), 3009-3012, Dec. 1,
Theoretical model investigations indicate that nitric acid may
substantially modify supercooled cirrus cloud at temperatures above -40°C,
and thereby influence climate.
"Multi-Spectral Calculations of the Direct Radiative Forcing of
Tropospheric Sulfate and Soot Aerosols Using a Column Model," J.M.
Haywood (NOAA/GFDL, POB 308, Princeton NJ 08542), K.P. Shine,Quart. J.
Royal Meteor. Soc., 123(543), 1907-1930, Oct. 1997 Part A.
Results from a newly developed multi-spectral radiative transfer code
show that subgrid-scale variations in relative humidity and the spatial
correlation between clouds and areas of high humidity should be considered
in GCM simulations. Recent estimates of the climate response to direct
forcing may be too large. The role of soot is discussed.
"Climate Change and Energy Policy: The Impacts and Implications of
Aerosols," J.J. West (Dept. Civil Eng., Carnegie Mellon Univ.,
Pittsburgh PA 15213; e-mail: email@example.com), C. Hope, S.N. Lane,Energy
Policy, 25(11), 923-939, Sep. 1997.
Isolates the effects of aerosols by treating their emissions as a policy
variable separate from greenhouse gas emissions, but linked through energy
policy. Using a simple climate model, questions the conclusion that
aerosols are beneficial to climate because they counteract greenhouse
warming. Instead, there is greater uncertainty in mean temperature, and a
greater likelihood of changes in other climate parameters.
"Contrail-Cirrus and Their Potential for Regional Climate Change,"
K. Sassen (Dept. Meteor., Univ. Utah, Salt Lake City UT 84112; e-mail:
firstname.lastname@example.org),Bull. Amer. Meteor. Soc., 78(9),
1885-1903, Sep. 1997.
Reviews the indirect evidence for the regional climatic impact of
contrail-generated cirrus clouds, and presents new measurements. The
evidence indicates that the direct radiative effects of contrails display
the potential for regional climate change at many midlatitude locations.
The sign of the impact may be uncertain, but new information favors albedo
cooling over a greenhouse warming effect.
"General Circulation Model Calculations of the Direct Radiative
Forcing by Anthropogenic Sulfate and Fossil-Fuel Soot Aerosol," J.M.
Haywood (NOAA/GFDL, POB 308, Princeton NJ 08542; e-mail: email@example.com),
D.L. Roberts et al.,J. Clim., 10(7), 1562-1577, July 1997.
Uses a new radiation code to assess the direct solar and thermal
radiative forcing of these species. Results are extremely sensitive to the
adopted soot/sulfate ratio and the assumed vertical profile, but they
indicate that fossil fuel soot aerosol may exert a nonneglible radiative
forcing, and emphasize the need to consider each anthropogenic aerosol
"Volcanic Sulfur Emissions: Estimates of Source Strength and Its
Contribution to the Global Sulfate Distribution," H.-F. Graf (M.
Planck Inst. Meteor., Bundestr. 55, D-20146 Hamburg, Ger.; e-mail:
firstname.lastname@example.org), J. Feichter, B. Langmann,J. Geophys. Res., 102(D9),
10,727-10,738, May 20, 1997.
Uses an atmospheric GCM with a full sulfur cycle and prescribed source
distributions. Results show that natural S sources are at least as
important as the anthropogenic ones, even though their source strength is
smaller, because of different lifetimes resulting from different
production and emission processes. Volatile volcanic sources should be
"Aerosols and Climate: Anthropogenic Emissions and Trends for 50
Years," M.E. Wolf (Radian Intl., 10389 Old Placerville Rd.,
Sacramento CA 95827; e-mail: email@example.com), G.M. Hidy,J.
Geophys. Res., 102(D10), 11,113-11,121, May 27, 1997.
Describes a global inventory of anthropogenic particulate emissions for
the period 1990-2040, including both primary particulate emissions and
secondary contributions from atmospheric chemical reactions, particularly
those involving SO2. Emissions worldwide, which are dominated
by fossil fuel combustion and biomass burning, are projected to grow by a
factor of 1.5 to 2.5 by 2040, largely from fossil fuel combustion in the
developing countries. Present anthropogenic emissions appear to be a small
fraction of emissions from natural sources, but could rival them by 2040.
The resulting increased haziness will alter the radiation budget of the
Earth, in a spatially non-uniform way.
"On Modification of Global Warming by Sulfate Aerosols," J.F.B.
Mitchell (Hadley Ctr., Meteor. Off., London Rd., Bracknell, Berkshire RG12
2SY, UK; e-mail: firstname.lastname@example.org), T.C. Johns,J. Clim.,
10(2), 245-267, Feb. 1997
Compares the patterns of response in the surface climatology of a
coupled ocean-atmosphere GCM forced by increases in CO2 alone,
to those associated with forcing by both CO2 and aerosols. In
winter, the cooling due to aerosols merely tends to reduce the response to
CO2, whereas in summer, it weakens the monsoon circulations
and reverses some of the changes in the hydrological cycle. Results of a
non-intervention scenario for CO2 and aerosols suggests that
future changes in aerosol concentrations would have a major effect on
regional climate, especially over Europe and Southeast Asia.
Special Issue: "Atmospheric Chemistry of Sulphur in Relation
to Aerosols, Clouds, and Climate," Phil. Trans. Royal Soc. London,
Series B, 352, Feb. 28, 1997. Contains 12 papers from a
discussion held July 1996, including the following:
"Climate Model Studies of Sulphate Aerosols and Clouds," A.
Jones (Hadley Ctr., Meteor. Off., London Rd., Bracknell, Berkshire RG12
2SY, UK), A. Slingo, 221-229. Summarizes recent work at the Hadley Centre
on the indirect effect of sulfate aerosols, which illustrates the
considerable uncertainty in estimating the indirect effect.
"The Missing Climate Forcing," J. Hansen (NASA Goddard Inst.
Space Studies, 2880 Broadway, New York NY 10025), M. Sato et al., 231-240.
Since the industrial revolution began, global warming has been only half
that expected due to the principal forcing, increasing greenhouse gases.
This paper argues on the basis of several lines of indirect evidence that
aerosol effects on clouds have caused a large negative forcing that has
substantially offset global warming. Observing and studying this effect
are extremely difficult, but are essential for the prognosis of future
"Atmospheric Sulfur and ClimateWhat Have We Learned?"
R.A. Cox (Ctr. Atmos. Sci., Univ. Cambridge, Lensfield Rd., Cambridge CB2
1EW, UK), 251-254. Summarizes the rest of the papers from the meeting. It
appears that the global distribution of atmospheric sulfur is such that
significant influences on atmospheric radiative transfer are possible, and
that the basic idea of a coupling between biological systems and climate
via atmospheric chemistry and clouds seems to be robust. But the processes
involved are even more complex than was first suggested by Charlson et al.
in their 1987 paper.
"Uncertainty in Climate Change Caused by Aerosols," S.E.
Schwartz (Brookhaven Natl. Lab, Upton NY 11973; e-mail: email@example.com), M.O.
Andreae,Science, 272(5265), 1121-1122, May 24, 1996.
A critique of the National Research Council report A Plan for a
Research Program on Aerosol Radiative Forcing and Climate Change
(April, 1996). The report, while basically sound, should have stressed the
urgency of reducing uncertainty in the role of aerosols in climate, and
seriously underestimates the research effort required to reduce this
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