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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 9, NUMBERS 10-11, OCTOBER-NOVEMBER 1996

PROFESSIONAL PUBLICATIONS...
GLOBAL & REGIONAL MODELING

Item #d96oct54

"Intercomparison of Hydrologic Processes in AMIP [Atmospheric Model Intercomparison Project] GCMs," K.-M. Lau (Atmos. Lab., Code 913, NASA-Goddard, Greenbelt MD 20771; e-mail: lau@climate.gsfc.nasa.gov), J.H. Kim, Y. Sud, Bull. Amer. Meteor. Soc., 77(10), 2209-2227, Oct. 1996.

Compares the current abilities of 29 GCMs to simulate regional and hydrologic processes in response to observations of sea surface temperature and sea ice boundary forcings. Most major features are reasonably well simulated, such as the global rainfall distribution, heavy precipitation associated with deep convection, and rainfall associated with the Southern Oscillation. Common problems include significant errors in the total global water balance (in about a quarter of the models), poor simulation of some features of the Asian monsoon, and underestimation of light rainfall. Validation of simulated discharge from the Amazon and Mississippi Rivers shows that it is premature to use GCMs for climate studies related to continental-scale water balance.

Item #d96oct55

"Effects of Cloud-Radiation Schemes on Climate Model Results," R.C.J. Somerville (Scripps Inst. Oceanog., La Jolla CA 92093), S.F. Iacobellis, W.-H. Lee, World Resource Review, 8(3), 321-333, Sep. 1996.

Feedbacks due to cloud-radiation interactions are thought to be the largest source of uncertainty in climate simulations. For too long there were too many plausible cloud-radiation parameterizations and too little effort to test them empirically. The effects on climate sensitivity of several cloud-radiation parameterizations were investigated with the NCAR Community Climate Model and validated with observations from field experiments. Schemes with explicit cloud water budgets and interactive radiative properties may be capable of matching observations closely. Now that appropriate observations and novel modeling tools are at last becoming available, we may anticipate rapid progress in this critical area.

Item #d96oct56

"The ISLSCP [Intl. Land Surface Climatology Project] Initiative I Global Datasets: Surface Boundary Conditions and Atmospheric Forcings for Land-Atmosphere Studies," P.J. Sellers, B.W. Meeson (Goddard Space Flight Ctr., NASA, Bldg. 28, Code 902.2, Greenbelt MD 20771; e-mail: meeson@daac.gsfc.nasa.gov) et al., Bull. Amer. Meteor. Soc., 77(9), 1987-2005, Sep. 1996.

Describes a comprehensive series of global data sets for land-atmosphere models that has been formatted to a common grid and released on a set of CD-ROMs. All data sets cover 1987-88, most at a monthly interval. The headings for the data sets are: vegetation; hydrology and soils; snow, ice, and oceans; radiation and clouds; and near-surface hydrology.

Item #d96oct57

"Polar Boundary Layer Plumes and Bottom Water Formation: A Missing Element in Ocean General Circulation Models," L.D.D. Harvey (Dept. Geog., Univ. Toronto, 100 St. George St., Toronto ON M5S 3G3, Can.; e-mail: harvey@geog.utoronro.ca), J. Geophys. Res., 101(C9), 20,799-20,808, Sep. 15, 1996.

Much of world's the deep water forms as relatively dense layer on shelves in polar regions, and flows downslope as a boundary layer plume. This process, omitted from current ocean GCMs, was investigated by coupling a 2-D plume model to a 2-D dynamical ocean model, and sea ice and surface climate models, and examining response to a greenhouse gas increase. Results indicate that polar plume processes should be incorporated in coupled atmosphere-ocean GCMs, but that correct simulation of the ocean density field and the surface forcing conditions are higher priorities. Incorporation of plumes could especially lead to more accurate representation of regional climatic responses.

Item #d96oct58

"Global Comparison of the Regional Rainfall Results of Enhanced Greenhouse Coupled and Mixed Layer Ocean Experiments: Implications for Climate Change Scenario Development," P.H. Whetton (Div. Atmos. Res., CSIRO, P.B. 1, Aspendale 3195, Victoria, Australia), M.H. England et al., Clim. Change, 33(4), 497-519, Aug. 1996.

Compares rainfall results from five models, which use a simple mixed layer ocean formulation, with results from five models which use a fully dynamic ocean model. For many regions in the Northern Hemisphere, there is strong agreement on the sign of the simulated rainfall change, but in the Southern Hemisphere there are large and apparently systematic differences. Concludes that it may be too soon to base some regionally specific climate change scenarios solely on the results of fully dynamic models.

Item #d96oct59

"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 #d96oct60

"Implications of a New Eddy Parameterization for Ocean Models," T.J. McDougall (Div. Oeanog., GPO Box 1538, Hobart 7001, Tasmania, Australia; e-mail: mcdougall@ml.csiro.au), A.C. Hirst et al., Geophys. Res. Lett., 23(16), 2085-2088, Aug. 1, 1996.

Demonstrates a new parameterization that yields deep ocean salinities and temperatures closer to those observed. In addition, the depth to which surface-induced tracers penetrate in the Southern Ocean is realistic. This depth is overestimated by previous ocean models, including those that estimate global warming. The new parameterization is expected to yield greater global warming.

Item #d96oct61

"A Case Study of the Adequacy of GCM Simulations for Input to Regional Climate Change Assessments," J.S. Risbey (129 Baker Hall, Carnegie Mellon Univ., Pittsburgh PA 15213; e-mail: risbey@andrew.cmu.edu), P.H. Stone, J. Clim., 9(7), 1441-1467, July 1996.

The Sacramento Basin is the focus of a case study to test whether a variety of GCMs from GISS and NCAR are capable of simulating the large-scale and synoptic-scale processes important in studies of regional water resources. In all the models, the stationary waves, jet streams, and storm tracks in the North Pacific-North America region show major differences from observations. The larger-scale fields necessary for driving nested models and impact models for the basin, or for western North America in general, are deficient, probably because of inadequate parameterization of sub-grid scale processes.

Item #d96oct62

Two related items in Nature, 382(6586), July 4, 1996:

"An Incriminating Fingerprint," N. Nicholls (Meteor. Bureau Res. Ctr., POB 1289K, Melbourne, Vic. 3001, Australia), 27-28. Gives a scientific perspective on the following article, which, despite several caveats, provides the most convincing demonstration yet that human actions may have contributed to global air temperature changes in this century.

"A Search for Human Influences on the Thermal Structure of the Atmosphere," B.D. Santer (Clim. Model Diagnosis, Lawrence-Livermore Natl. Lab., POB 808, Livermore CA 94550), K.E. Taylor et al., 39-46. Uses climate model simulations to examine changes in the vertical structure of atmospheric temperature as a "fingerprint" of human influence on climate. The study differs from similar ones in four respects: (1) it includes the combined influence of CO₂ and anthropogenic sulfate aerosols on the vertical pattern; (2) two different models are used, to examine model-dependent uncertainties; (3) the possible effects of changes in stratospheric ozone are examined; (4) control runs with coupled ocean-atmosphere models are used to estimate internally generated natural climate variability. Simulations of the spatial patterns of temperature change in the free atmosphere from 1963 to 1987 are similar to those observed, and the degree of similarity increases through the period. The observed trend is probably partly due to human activities, although many uncertainties remain, particularly relating to estimates of natural variability. The investigation shows a clear need for modeling experiments that combine simultaneous changes in CO₂, O3 and anthropogenic sulfate aerosols.

Item #d96oct63

"Evaluation of Simulations of Terrestrial Precipitation in UK Met. Office/Hadley Center Climate Change Experiments," M.H. Airey (Clim. Res. Unit., Univ. E. Anglia, Norwich NR4 7TJ, UK), M. Hulm, T.C. Johns, Geophys. Res. Lett., 23(13), 1657-1660, June 15, 1996.

Evaluates four successive versions of the Hadley GCM by comparing precipitation fields over land from the control integrations with observed precipitation. Globally, improvements in simulating mean monthly precipitation patterns occur with successive versions. The later versions show improvement in the South Asian summer monsoon, the pattern of temporal variability, and the pattern of temporal correlation between the Southern Oscillation Index and precipitation anomalies.

Item #d96oct64

"Documentation of the AMIP [Atmospheric Model Intercomparison Project] Models on the World Wide Web," T.J. Phillips (Clim. Model Diagnosis & Intercomparison, L-264, Lawrence-Livermore Natl. Lab., POB 808, Livermore CA 94551; e-mail: phillips@tworks.llnl.gov), Bull. Amer. Meteor. Soc., 77(6), 1191-1196, June 1996.

Launched in 1991, AMIP led to a 1994 report documenting the summaries, dynamics, and physics of 30 participating models in a common and reasonably comprehensive framework. Now, constant updates of that information are available on the World Wide Web at http://www-pcmdi.llnl.gov/phillips/modldoc/amip/amip.html, with hypertext links to more detailed information.

Item #d96oct65

Two items in J. Geophys. Res., 101(D8), May 27, 1996:

"Cloud Feedback in Atmospheric General Circulation Models: An Update," R.D. Cess (Inst. Terrestrial & Planetary Atmos., Marine Sci. Ctr., SUNY, Stony Brook NY 11794), M.H. Zhang et al., 12,791-12,794. A comparison of the climate sensitivity of 19 GCMs six years ago found a roughly threefold variation among the models, mostly attributed to differences in depictions of cloud feedback. In an update of this comparison, current models showed considerably smaller differences in net cloud feedback. However, there are still substantial differences in the feedback components, showing that physical disagreements remain.

"High Latitude Climate Change in a Global Coupled Ocean-Atmosphere-Sea Ice Model with Increased Atmospheric CO₂," W.M. Washington (NCAR, POB 3000, Boulder CO 80307), G.A. Meehl, 12,795-12,801. Describes an increasing CO₂ simulation using improved versions of models from previous experiments, including a 1° by 1° , 20-level ocean GCM. The models produce an anomalous warm layer of water at depths between 200 and 400 meters, which resembles an anomalous warm layer recently observed in the Arctic. The ice albedo feedback is strong, leading to comparatively high climate sensitivity.

Item #d96oct66

"A 3D Model Study of the Global Sulphur Cycle: Contributions of Anthropogenic and Biogenic Sources," M. Pham (Service d'Aéronomie, 4 Pl. Jussieu, 75 252 Paris Cedex 05, France), J.F. Müller et al., Atmos. Environ., 30(10/11), 1815-1822, May 1996.

Compares simulations of the preindustrial and present-day atmospheres produced by the IMAGES 3-D tropospheric chemistry-transport model. They show a large postindustrial increase in the concentrations of SO2 and non-sea-salt sulfates, amounting to a factor of 2 or 3 on a global average, and reaching two orders of magnitude at the surface in some parts of the Northern Hemisphere. Biogenic species such as DMS are also shown to be influenced by industrialization through changes in the oxidizing capacity of the atmosphere.

Item #d96oct67

"Parameterizations of Marine Stratus Microphysics Based on In Situ Observations: Implications for GCMs," I. Gultepe (Cloud Phys. Res. Div., Atmos. Environ. Serv., 4905 Dufferin St., Downsview ON M3H 5T4, Can.), G.A. Isaac et al., J. Clim., 9(2), 345-357, Feb. 1996.

Airborne observations conducted in marine stratus over the east coast of Canada are used to develop cloud microphysical parameterizations schemes for general circulation models. Results show that multiple relationships are present among various microphysical properties, depending in part on variations in both aerosol concentrations and cloud dynamic activity. Parameterized equations must be used in GCMs with caution.

Item #d96oct68

"Temperature Depression in the Lowland Tropics in Glacial Times," P.A. Colinvaux (Smithsonian Tropical Res. Inst., POB 2072, Balboa, Panama), K.-B. Liu et al., Clim. Change, 32(1), 19-33, Jan. 1996.

Presents pollen and other data confirming the recently recognized existence of a general tropical cooling during the last ice age. Climate models used to predict future effects of greenhouse gases must also be able to simulate the significant cooling of the large tropical land masses at glacial times with reduced greenhouse gas concentrations.

Item #d96oct69

"Construction of a 1961-1990 European Climatology for Climate Change Modellng and Impact Applications," M. Hulme (Clim. Res. Unit, Univ. E. Anglia, Norwich NR4 7TJ, UK), D. Conway et al., Intl. J. Climatol., 15(12), 1333-1363, Dec. 1995.

A mean monthly climatology has been constructed at a resolution of 0.5° latitude by 0.5° longitude for nine surface climate variables. Details of construction and interpolation to the grid points are discussed. This unique data base is being used by researchers for ecosystem modeling, climate change impact assessment and climate model validation; it is available from the authors.