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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 8, NUMBER 12, DECEMBER 1995

PROFESSIONAL PUBLICATIONS...
GLOBAL MODELING

Item #d95dec11

"Climate Models: How Reliable Are Their Predictions?", E.J. Barron (Earth Systems Sci. Ctr., Deike Bldg., Pennsylvania State Univ., Univ. Pk. PA 16802), Consequences, 1(3), 16-27, Autumn 1995.

Computer-based general circulation models are modified versions of the mathematical simulations that have been used for decades to forecast weather. Many now in use around the world have been independently derived and are continually compared and evaluated for their ability to reproduce documented climate features of the past. However, because they are based on our present, evolving knowledge of how the climate system operates and have coarse spatial resolution, their projections of future climate are cast in terms of a range of uncertainty. Nevertheless, they are our best and only hope of anticipating future changes in climate, and we only lose if we dismiss their findings, outright, as too equivocal or theoretical or incomplete. Choices of whether or how to act on what is predicted are best made with a knowledge of both the strengths of these tools and their weaknesses. We can count on continued improvements in model reliability.

Item #d95dec12

"Mapping the Land Surface for Global Atmosphere-Biosphere Models: Toward Continuous Distributions of Vegetation's Functional Properties," R.S. DeFries (Dept. Geog., Univ. Maryland, College Pk. MD 20742), C.B. Field et al., J. Geophys. Res., 100(D10), 20,867-20,882, Oct. 20, 1995.

Reviews several existing land surface classification schemes commonly used as important boundary conditions in atmosphere-biosphere models. Considers the functional properties of vegetation required to calculate parameter fields used in global models, and suggests an approach for describing the land surface using continuous distributions of these functional properties.

Item #d95dec13

"Distribution and Budget of O3 in the Troposphere Calculated with a Chemistry General Circulation Model," G.-J. Roelofs (POB 8129, 6700 EV, Wageningen, Neth.), J. Lelieveld, ibid., 20,983-20,998.

Presents results of global tropospheric chemistry simulations with the coupled chemistry-atmospheric general circulation model ECHAM, which will eventually be used to study climate changes through anthropogenic influences on the chemistry of the atmosphere. Comparisons of calculated O3 surface concentrations and O3 profiles with data show that the model reproduces O3 distributions in remote tropical and midlatitude sites, but underestimates concentrations at the poles and in relatively polluted areas. Discusses the model deficiencies that are responsible and how they will be improved.

Item #d95dec14

"On Surface Temperature, Greenhouse Gases, and Aerosols: Models and Observations," J.F.B. Mitchell (Hadley Ctr., Meteor. Off., London Rd., Bracknell, Berkshire RG12 2SY, UK), R.A. Davis et al., J. Clim., 8(10), 2364-2386, Oct. 1995.

Presents further results from the U.K. Meteorological Office GCM incorporating the effects of sulfate (industrial) aerosol, which has already been shown to improve model simulations of the observed temperature record. The addition of aerosols has little impact on the reduction of diurnal range of surface temperature that accompanies increased CO₂. (This is a sequel to the author's paper in the Aug. 10, 1995 issue of Nature, listed in Prof. Pubs./Of Gen. Interest/CLouds and Aerosols, GLOBAL CLIMATE CHANGE DIGEST, Sep. 1995.)

Item #d95dec15

"Land Surface Process Models Discussed in Interdisciplinary Forum," A. Henderson-Sellers (Clim. Impacts Ctr., Macquarie Univ., North Ryde, Sydney, SW 2109, Australia), Eos, 76(38), 369, 379, Sep. 19, 1995.

Summarizes a joint symposium on the status of land surface process models held during the IUGG 21st Assembly (Boulder, Colorado, July 1995).

Item #d95dec16

"Land Surface Processes and Climate Modeling," R.E. Dickinson (Inst. Atmos. Phys., Univ. Arizona, Tucson AZ 85721), Bull. Amer. Meteor. Soc., 76(8), 1445-1448, Aug. 1995.

An overview of the current status of the representation of land surface processes in climate models, originally presented as the 1995 AMS Walter Orr Roberts Lecture. With the increasing complexity and importance of these parameterizations and their detailed treatments of the roles of soils and vegetation, have come greater demands for observational programs to evaluate their success and to provide required parameters. Further improvement is most needed in model treatments of precipitation, cloud effects on surface radiation, and boundary layer processes.

Item #d95dec17

"A Transient CO₂ Experiment with the MRI CGCM—Quick Report," T. Tokioka (Japan Meteor. Agency, Tokyo 100, Japan), A. Noda et al., J. Meteor. Soc. Japan, 73(4), 817-826, Aug. 1995.

Demonstrates application of the Meteorological Research Institute (MRI) coupled atmosphere-ocean GCM, which has an elaborate model of the seasonal variation of sea ice coverage and thickness, and a high resolution ocean component in the low latitudes for simulating El Niño behavior. In a 70-year time integration, atmospheric response to CO₂ increase is slower for the Southern Hemisphere and ocean areas, but the surface temperature increase in the Northern Hemisphere does not dominate for the first 50 years. Leads in sea ice act as a strong negative feedback on changes in sea ice volume, influencing the timing of the warming.

Item #d95dec18

"Recent Northern Winter Climate Trends, Ozone Changes and Increased Greenhouse Gas Forcing," H.-F. Graf (M. Planck Inst. Meteor., Bundesstr. 55, 20146 Hamburg, Ger.), J. Perlwitz et al., Beitr. Phys. Atmos., 68(3), 233-248, Aug. 1995.

Ozone data of the past 15-20 years show an increase in upper tropospheric O3 and a decrease in lower stratospheric O3. These changes are discussed against the background of meteorological data and GCM simulations of the effects of increased greenhouse gas concentration, aerosols, and the modified ozone profile itself. Concludes that a comprehensive climate model, including atmospheric chemistry and a good representation of the stratosphere, is needed to study future climate scenarios, and that greenhouse gas effects and ozone concentration are probably not independent.

Item #d95dec19

"The Dependence of Climate Sensitivity on the Horizontal Resolution of a GCM," C.A. Senior (Hadley Ctr., Meteor. Off., London Rd., Bracknell, Berkshire RG12 2SY, UK), J. Clim., 8(11), 2860-2880, Nov. 1995.

The use of higher resolution in the Hadley Center model generally produces favorable changes in present-day and doubled CO₂ simulations. The global mean annual-mean warming due to increased CO₂ is very similar, but there are differences in the latitudinal distribution of the zonally averaged temperature response, which in winter is related to the response of Northern Hemisphere storm tracks.

Item #d95dec20

"The Sulfate-CCN-Cloud Albedo Effect: A Sensitivity Study with Two General Circulation Models," O. Boucher (Lab. Météor. Dynamique, CNRS, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris cedex 05, France), U. Lohmann, Tellus, 47B(3), 281-300, July 1995.

Anthropogenic sulfate particles have an indirect cooling effect because they induce the formation cloud droplets, which reflect sunlight. This study estimates the magnitude of the effect by empirically relating the cloud droplet number concentration to the sulfate aerosol mass concentration derived from a chemical transport model. Experiments using this information in two GCMs indicate a globally-averaged indirect forcing of about -1 W m-2. The value in different experiments ranged from -0.5 to -1.5 W m-2, but the range of uncertainty is certainly greater. The highest forcings occur in and off the coasts of the polluted regions of the Northern Hemisphere.

Item #d95dec21

"Analysis of Snow Feedbacks in 14 General Circulation Models," D.A. Randall (Dept. Atmos. Sci., Colorado State Univ., Fort Collins CO 80523), R.D. Cess et al., J. Geophys. Res., 99(D10), 20,757-20,771, Oct. 20, 1994.

Results of 14 GCMs were compared through idealized numerical experiments in which the surface energy budgets of the models were analyzed. The feedbacks were negative or weakly positive in some of the models, but strongly positive in others, and in each case were determined by a complex mix of factors.