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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 10, NUMBER 3, MARCH 1997

PROFESSIONAL PUBLICATIONS...
CLOUDS, AEROSOLS & CLIMATE

Item #d97mar38

"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: jfbmitchell@meteo.gov.uk), J. Clim., 10(2), 245-267, Feb. 1997.

Compares patterns of response in the surface climatology of a coupled ocean-atmosphere general circulation model forced by increased CO₂ alone, to patterns caused by forcing from both CO₂ and aerosols, from early industrial times to the end of the 21st century. Comparisons for 2030-2050, when the aerosol forcing is a maximum, showed that in summer, the cooling due to aerosols weakens the monsoon circulations and reverses some of the changes in the hydrologic cycle caused by greenhouse gases. Changes in aerosol concentrations of the magnitude projected in the scenarios would have a major effect on regional climate, especially over Europe and Southeast Asia.

Item #d97mar39

Two items in J. Geophys. Res., 102(D3), Feb. 20, 1997:

"A Comparison of the Stratospheric Aerosol Background Periods of 1979 and 1989-1991," L.W. Thomason (Atmos. Sci. Div., MS-475, NASA-Langley Res. Ctr., Hampton VA 23681; e-mail: thomason@larc.nasa.gov), G.S. Kent et al., 3611-3616. Previous examination of increased aerosol concentration between these two periods has been interpreted as evidence that human activity may already have significantly affected the stratospheric aerosol burden. This analysis strongly suggests that the stratosphere was still influenced by volcanic eruptions in the latter period, and that any underlying anthropogenic influence must be smaller than has been suggested previously.

"An Assessment of the Radiative Effects of Anthropogenic Sulfate," C.C. Chuang (Atmos. Sci. Div. L-103, Lawrence-Livermore Natl. Lab., POB 808, Livermore CA 94550; e-mail: cathy@hualien.llnl.gov), J.E. Penner et al., 3761-3778. Uses a coupled climate-chemistry model with cloud nucleation processes to investigate both direct and indirect sulfate radiative forcings. Estimates a global direct radiative forcing of about -0.4 W m-2, with a maximum over Europe where the strongest anthropogenic sulfur emissions occur. Different approaches for estimating the indirect forcing yield a range of -0.6 to -1.6 W m-2. Simulations indicate that anthropogenic sulfate may cause important increases in reflected solar radiation, which would mask locally the warming from greenhouse gases.

Item #d97mar40

"Greenhouse Warming versus Aerosol Cooling in the Context of Global Climate Change: Contribution of Satellite Observations," K. Ya. Kondratyev (Russian Acad. Sci., Ctr. Ecol. Safety, 18 Korpusnaya St., 197042 St. Petersburg, Russia), World Resource Review, 8(4), 456-466, Dec. 1996.

Atmospheric aerosols undoubtedly play an important role in climate change, but since global climate modeling is still at an early stage of development, the decisive role in research belongs to observations. Reviews results from Russian field programs that bear on the problem, and discusses the urgent need to optimize the Global Climate Observing System with regard to combined use of conventional and satellite observations.

Item #d97mar41

"Sensitivity of Simulated Global Climate to Perturbations in Low Cloud Microphysical Properties. Part II: Spatially Localized Perturbations," C.-T. Chen, V. Ramaswamy (NOAA/GFDL, POB 308, Princeton NJ 08542), J. Clim., 9(11), 2788-2801, Nov. 1996.

Two types of spatially localized perturbations were incorporated into GCM simulations and compared with previous results for globally uniform cloud properties. The perturbations were imposed in the midlatitude Northern Hemisphere and covered either the entire zone (simulating effects of anthropogenic sulfate emissions) or were limited to land areas (simulating observed land-ocean differences in microphysical properties). The model's climate sensitivity was found to be independent of the distribution and magnitude of forcing, but individual feedback mechanisms were dissimilar. The localized experiments induced notable changes in the mean meridional circulation and precipitation near the equator.

Item #d97mar42

"Climate Implications of Biomass Burning Since the 19th Century in Eastern North America," J.S. Clark (Dept. Botany, Duke Univ., Durham NC 27708), B.J. Stocks, P.J.H. Richard, Global Change Biology, 2(5), 433-442, Oct. 1996.

Recent predictions that tropospheric aerosols have counterbalanced greenhouse warming assume aerosol emissions were low before 1850 and then increased dramatically with industrialization of the Northern Hemisphere and biomass burning in the tropics. This analysis of the lake sediment record of emissions across North America indicates that aerosols could have actually decreased during the 20th century, suggesting that the offset hypothesis requires further analysis using different assumptions of past emissions. [The following entry relates to this topic.]

Item #d97mar43

"Predicting Cloud-Droplet Effective Radius and Indirect Sulphate Aerosol Forcing Using a General Circulation Model," A. Jones (Hadley Ctr., Meteor. Off., London Rd., Bracknell, Berkshire RG12 2SY, UK; e-mail: ajones@meto.gov.uk), A. Slingo, Quart. J. Royal Meteor. Soc., 122(535), 1573-1595, Oct. 1996 Part A.

Effects of different parameterization approaches and different input sulfate data sets are examined in simulations corresponding to a period since the start of the industrial era. Results demonstrate the need for a much better understanding of the links among sulfate aerosol mass concentrations, cloud condensation nuclei, and cloud-droplet number concentrations.

Item #d97mar44

"Airborne Particle Analysis for Climate Studies," T. Peter (Max Planck Inst. Chemie, Mainz, Ger.; e-mail: peter@nike.mpch-mainz.mpg.de), Science, 273(5280), 1352-1353, Sep. 6, 1996.

A commentary on how new in situ particle analysis techniques could benefit study of the climatic impact of anthropogenic particles, and polar stratospheric clouds.

Item #d97mar45

Two items in J. Geophys. Res., 101(D13), Aug. 20, 1996:

"A Global Three-Dimensional Model of Tropospheric Sulfate," M. Chin (NASA-Goddard, Code 916, Greenbelt MD 20771; e-mail: chin@gator1.gsfc.nasa.gov), D.J. Jacob et al., 18,667-18,690. Presents a model based on the GCM developed at the Goddard Institute for Space Studies, which differs from previous such models in several respects, and is used in the following paper.

"Anthropogenic and Natural Contributions to Tropospheric Sulfate: A Global Model analysis," M. Chin (address above), D.J. Jacob, 18,691-18,699. Results from the model described in the previous paper indicate that about 40% of the anthropogenic sulfur emitted in the U.S., Europe or eastern Asia is exported out of the continental boundary layer of these regions. The rest is removed within the regions, primarily by dry deposition of SO2 and wet deposition of SO42-. Anthropogenic influence on SO42- decreases rapidly with height, and it accounts on average for less than 20% of SO42- anywhere in the upper troposphere. Because of the rapid deposition of anthropogenic SO2 and SO42- at low altitudes, the anthropogenic contribution to the SO42- aerosol optical depth is much less than would be expected simply on the basis of emissions.

Item #d97mar46

"The Cloud Absorption Anomaly-What Problem?" R.S. Scorer (Imperial College, London), Weather, 51(8), 288-290, Aug. 1996.

A veteran cloud observer and analyst proposes a mechanism to explain why clouds absorb more sunshine than is predicted by present mathematical models.

Item #d97mar47

"Global Warming," M. Hulme (Clim. Res. Unit., Univ. E. Anglia, Norwich NR4 7TJ, UK), Prog. in Phys. Geog., 20(2), 216-223, 1996.

A review of recent scientific literature focusing on the role of atmospheric aerosols in contemporary climate change.

Item #d97mar48

"Direct Radiative Forcing by Anthropogenic Airborne Mineral Aerosols," I.N. Sokolik (Earth Sci. Div., NASA-Ames, MS-245-4, Moffett Field CA 94035), O.B. Toon, Nature, 381(6584), June 20, 1996.

Estimates of anthropogenic inputs of mineral dust to the atmosphere, combined with observations of its optical properties, suggest that the forcing by anthropogenic mineral aerosols (from grazing, construction, mining and the like) may be comparable to the forcing by other anthropogenic aerosols (sulfate and smoke). On a regional scale, the forcing due to mineral aerosols can greatly exceed that due to sulfate aerosols and can be comparable to that of clouds. Specifies the key quantities that must be better characterized to reduce the large uncertainties in these estimates.

Item #d97mar49

"Absorption of Solar Energy in the Atmosphere: Discrepancy Between Model and Observations," A. Arking (Dept. Earth & Planetary Sci., Johns Hopkins Univ., Baltimore MD 21218; e-mail: arking@aa.gsfc.nasa.gov), Science, 273(5276), 779-782, Aug. 9, 1996.

Calculations made by an atmospheric general circulation model were compared with observations of the flux of solar radiant energy based on a combination of ground-based and satellite measurements. The model underestimated the amount of solar energy absorbed by the Earth's atmosphere by 25 to 30 watts per square meter. Contrary to some recent reports, clouds have little or no overall effect on atmospheric absorption; water vapor seems to have the dominant influence.

Item #d97mar50

"Climate Forcing and the Physico-Chemical Life Cycle of the Atmospheric Aerosol-Why Do We Need an Integrated, Interdisciplinary Global Research Program?" J. Heintzenberg (Inst. Tropospheric Res., Permoserstr. 15, 04303 Leipzig, Ger.), H.-F. Graf et al., Beitr. Phys. Atmos., 69(2), 261-271, May 1996.

A peer-reviewed editorial arguing for research needed to include the atmospheric aerosol as a prognostic variable in global models of climate and trace substances. Formulates a program for integrated, interdisciplinary aerosol research that combines in situ physical and chemical aerosol characterization, remote sensing, and modeling. Essential is the integration of key activities which will not achieve the desired result if pursued individually.

Item #d97mar51

"Clouds and the Earth's Radiant Energy System (CERES): An Earth Observing System Experiment," B.A. Wielicki (Atmos. Sci. Div., MS-420, NASA-Langley Res. Ctr., Hampton VA 23681), B.R. Barkstrom et al., Bull. Amer. Meteor. Soc., 77(5), 853-868, May 1996.

The CERES program will extend and improve on the Earth Radiation Budget Experiment (ERBE) by flying broadband scanning radiometers on several NASA-EOS satellites starting in 1998 and extending over at least 15 years. CERES will also combine simultaneous cloud property data derived using EOS narrowband imagers to provide a consistent set of cloud/radiation data at the surface and at several selected levels of the atmosphere. [Technical details are available at http://asd-www.larc.nasa.gov/ceres/docs.html]

Item #d97mar52

"The Greenhouse Earth: A View from Space," J.E. Harries (Imperial College of Science, Blackett Lab., Imperial College, London SW7 2BZ, UK), Quart. J. Royal Meteor. Soc., 122(532), 799-818, Apr. 1996 Part B.

A review. Radiative cooling of the Earth in the absence of clouds has recently been shown to be dominated by emission from water vapor in the upper troposphere. The role of clouds is presently less clear, but in both cases, more accurate global observations are needed. The paper is illustrated by data from satellite experiments.

Item #d97mar53

"Observations of Near-Zero Ozone Concentrations Over the Convective Pacific: Effects on Air Chemistry," D. Kley, P.J. Crutzen et al., Science, 274(5285), 230-233, Oct. 11, 1996.

Measurements made over the equatorial Pacific showed ozone levels frequently below 10 nanomoles per mole both in the marine boundary layer and between 10 km and the tropopause. These results emphasize the enormous variability of tropical tropospheric ozone and hydroxyl concentrations. They also imply a convective short circuit of marine gaseous emissions, such as dimethyl sulfide, between the sea surface and the upper troposphere, leading, for instance, to sulfate particle formation.

Item #d97mar54

"Historical Biomass Burning: Late 19th Century Pioneer Agriculture Revolution in Northern Hemisphere Ice Core Data and Its Atmospheric Interpretation," G. Holdsworth (Arctic Inst. of North America, Univ. Calgary, Calgary AB T2N 1N4, Can.; e-mail gholdswo@acs. ucalgary.ca), K. Higuchi et al., J. Geophys. Res., 101(D18), 23,317-23,334, Oct. 27, 1996.

Ice core data from Yukon and Greenland from about 1750 to 1950 show a clear atmospheric signal of an episode of biomass burning between about 1850 and 1910, which has been referred to elsewhere as the Pioneer Agriculture Revolution. The relationships of this finding to other types of climatic data are explored. It appears that factors associated with the burning, such as changes in surface albedo and atmospheric dust and smoke, caused local cooling and temporarily negated any radiative gas greenhouse warming.

Item #d97mar55

"Unexpectedly Low Ozone Concentration in Midlatitude Tropospheric Ice Clouds: A Case Study," J. Reichardt (GKSS-Forschungszentrum Geesthacht, Postfach 1160, 21494 Geesthacht, Ger.; e-mail: jens.reichardt@ gkss.de), A. Ansmann et al., Geophys. Res. Lett., 23(15), 1929-1932, July 15, 1996.

Raman lidar measurements of ozone, water vapor, and cirrus optical properties made in the early stages of a long-term program show pronounced ozone minima in the presence of ice cloud layers. Results warrant an extensive study of the possible influence on tropospheric ice clouds on the upper tropospheric ozone budget.