Research Strategies for the U.S. Global Change Research Program (1990) / Chapter Skim
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2 Integrated Modeling of the Earth System
2 Integrated Modeling of the Earth System
Pages 16-66
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From page 16... ...
Members of the group on Terrestrial-Atmosphere Modeling were Berrien Moore III, University of New Hampshire, Chair; John Aber, University of New Hampshire; Guy Brasseur, National Center for Atmospheric Research; Robert Dickinson, National Center for Atmospheric Research; William Emanuel, Oak Ridge National Laboratory; Jerry Melillo, 16
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From page 17... ...
Members of the group on Ocean-Atmosphere Modeling were Berrien Moore III, University of New Hampshire, Chair; Mark Abbott, Oregon State University; Curt Covey, Lawrence Livermore National Laboratory; Nick Graham, Scripps Institution of Oceanography; Dale Haidvogel, Johns Hopkins University; Eileen Hoffman, Old Dominion University; Christopher Mooers, University of New Hampshire; James O'Brien, Florida State University; Albert Semtner, Naval Postgraduate School; and Leonard Walstad, Oregon State University. Members of the group on Atmospheric Physics-Atmospheric Chemistry were Berrien Moore III, University of New Hampshire, Chair; Guy Brasseur and Robert Dickinson, National Center for Atmospheric Research; Bill Gross, NASA Langley Research Center; and Chris Morris, University of New Hampshire.
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From page 18... ...
The atmospheric models and their climate role are especially strongly governed by water processes; however, it is precisely these aspects, including questions of scale and parameterization, that are among the least satisfactory of the models. Resolution is a problem in that the spatial scales of many of the important atmospheric water structures are poorly resolved by existing models.
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From page 19... ...
Ecological changes, such as successional sequences of tree species, are not well treated on time steps that are appropriate for considering photon input and: water exchange or even trace gas fluxes and require some intermediate parameterization or model. The relatively simple coupling issue of land hydrology and atmosphere remains elusive, and yet it is quite important.
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From page 20... ...
For the near term, developments in modeling the earth system should continue to focus on linking previously unlinked components, adding specific subsystems to existing models (e.g., coupling oceanic and atmospheric GCMs or adding a marine biospheric model to an oceanic GCM) , or improving existing linked treatments.
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From page 21... ...
In order to provide perspective on the remainder of the chapter, the following considerations for each of the three interface models are provided: For models that couple the terrestrial ecosystems and the atmosphere: · The coupling must address questions such as how will a changing climate affect terrestrial carbon dioxide uptake and storage; how will · · . evapotransp~rat~on change; how will the distribution of vegetation and its seasonal pattern change; what are the effects on climate of changing patterns of vegetation, including large-scale deforestation; and what is the effect of changing chemical conditions on terrestrial vegetation and trace gas exchange?
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From page 22... ...
Future progress will be dependent both on available computational resources and on progress in developing our understanding of fundamental physical and chemical processes and the nature of their coupling. For models that couple the ocean and the atmosphere: · The coupling must address questions such as how will changing climate affect oceanic carbon dioxide uptake and storage; how will oceanic heat storage and transport change; how will the amount and distribution of primary production change; how will the marine hydrological cycle change; and how will a changing ocean affect a changing climate?
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From page 23... ...
Prototype global experiments will be especially important to exploring feedbacks between the production of longlived trace gas species and climate. Two important themes are important in early testing of partial earth system models: the global carbon cycle (carbon dioxide, methane, and carbon monoxide)
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From page 24... ...
The structure of terrestrial ecosystems, which responds on even longer time scales, is the integrated response to the intermediate time scale carbon machinery. The loop is closed back to the climate system since it is the structure of ecosystems, including species composition, that sets the terrestrial boundary condition in the climate system from the standpoint of surface roughness, albedo, and, to a great extent, latent heat exchange.
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From page 25... ...
Modeling these interactions requires coupling successional models to biogeochemical models to physiological models that describe the exchange of water and energy between the vegetation and the atmosphere at fine time scales. There does not appear to be any obvious way to allow direct reciprocal coupling of GCM-type models of the atmosphere, which inherently run with fine time constants, to ecosystem or successional models, which have coarse temporal resolution, without the interposition of a physiological model.
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From page 26... ...
NPP TOTAL) DECOMPOSITION / MINERALIZATION / UPTAKE NET CARBON EXCHANGE / NET ECOSYSTEM PRODUCTION FIGURE 2.3 Three different time steps at which existing models of terrestrial ecosystems use climatic information to modify rates of ecosystem function.
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From page 27... ...
Changes in soil solution chemistry and microbial processes can be captured at this level for calculation of trace gas fluxes. Primary outputs from this level of model are carbon and nutrient fluxes, biomass, leaf area index, and canopy height or roughness.
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From page 28... ...
. These models capture seasonal phonology and use summary climate data to calculate water, carbon, and nugget balances at monthly time steps.
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From page 29... ...
I TYPE T 1 ~WTN l l SL I ... I _ NITROGEN I AVAILABILITY 1 GROWTH UGHT _ ULTIPUERS AVAILABILITY ~l ~, \ TRANSFER l l \ NEW INmAL l I ~COHORTS ~ F · H ~ ~ ~1 _ ~I MINERAL SOIL | 29 1~4h40~LIZAnON ~, FIGURE 2.6 At the annual time step, models make use of the wealth of data available for growth and mortality of individual stems by species, or growth rate of entire stands of vegetation in relation to annual summations of climatic conditions.
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From page 31... ...
Nutrient cycling and soil chemistry modules can run under altered climatic drivers for some time, and then predictions can be made of the consequences of changes in ecosystem state for surface-atmosphere interactions and trace gas fluxes. This approach is consistent with those outlined in chapters 5 and 6, on water-energy-vegetation interactions and terrestrial trace gas and nutrient fluxes, respectively.
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From page 32... ...
The different levels of models have differing data requirements, and these must guide the collection and archiving of data. In addition to the coupled models, a parallel course needs to be pursued wherein detailed models should be developed that can allow analysis of ecosystem responses to forcing from scenarios of climatic change (i.e., those scenarios developed by exercising the first-generation earth system models)
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From page 33... ...
Specific extended model studies will address coupled responses of climate and terrestrial ecosystems, perturbation of the global element cycles through the effects of chemical or climatic change on terrestrial ecosystems, and analyses of the effects of land use and terrestrial resource use patterns on the dynamics of climate and element cycling. Key modeling themes include the following: · Coupled responses of climate and terrestrial ecosystems.
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From page 34... ...
Changes in the geographic patterns in the amplitude and phase of the annual cycle of atmospheric carbon dioxide concentration may be an early indicator of terrestrial ecosystem responses to climatic change. Major model experiments will address these responses of the terrestrial components of the global element cycles to climatic change.
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From page 35... ...
Long-time-scale ecological models that emphasize carbon and element storage and population dynamics can be driven by integrations of climate models, but their primary feedback is through the carbon budget and surface roughness. Carbon exchange, net ecosystem production, and trace gas biogeochemistry are best treated at an intermediate time scale and provide feedback to the atmosphere through trace gas exchange and water budgets.
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From page 36... ...
PHYSICAL-CHEMICAL INTERACTIONS IN THE ATMOSPHERE Models of the physical processes in the atmosphere provide much of our current basis for understanding future climatic change. However, there are still considerable shortcomings in their formulation and implementation, and thus they provide very uncertain projections for the future.
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From page 37... ...
The relative simplicity of these models has allowed both the development of conceptual descriptions of the various feedbacks that determine the response of global temperature to changes in radiative forcing and the development of more detailed and accurate radiative models for atmospheric gases and clouds. Hence the initial evaluation of the contributions of various trace gases to global warming has exclusively made use of such models.
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From page 38... ...
38 to o ~ ,~ , oz~ al m I LL cn ~ O _ e" e ~ LL ~ o ~ ~({ 2 y O ~ gHEUL c0 111 ~ 1- ~ S O In ~ O /~1 C ~ if- ~ F ,~ ~ , ° {L 3 ~ ~ .~ ~ o ~ ~ a.
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From page 39... ...
, about numerical drift apparent in coupled atmospheric-oceanic GCMs. Future changes in the earth system will probably result from increasing emissions (and atmospheric concentrations)
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From page 40... ...
More recently, atmospheric chemistry studies have relied upon two-dimensional models. These models solve the zonally averaged momentum, thermodynamic, and mass continuity equations, including detailed treatment of chemical and radiative processes.
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From page 41... ...
These reaction rates are functionally dependent on available particle surface area. Microphysical models that can describe the growth rate and size distribution of the cloud particles are thus an integral requirement for including heterogeneous reactions in atmospheric chemistry models.
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From page 42... ...
Finally, current atmospheric models suffer from serious deficiencies that detract from their use to study atmospheric chemistry. A critical deficiency is the inadequate treatment of cloud processes and the hydrological cycle in general.
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From page 43... ...
Because of the uneven distribution of emission sources at the surface of the earth and the role of meteorological processes at various scales, models of chemically active trace gases in the troposphere should be three-dimensional and resolve transport processes at the highest possible resolution. These models should be designed to simulate the chemistry and transport of atmospheric tracers on a global and regional scale, with accurate parameterizations of important subscale processes.
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From page 45... ...
(3) Transport processes by advection and convection will be illuminated through the development of high-resolution transport models coupled to atmospheric GCMs with detailed representation of physical processes including cloud formation and boundary layer transport.
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From page 46... ...
For example, in the context of a possibly changing climate under a given scenario of anthropogenic production of carbon dioxide what can be said about: the ocean) _ uptake and transport of carbon dioxide; the oceanic uptake and transport of heat; the distribution of new and total oceanic primary production; and, what will be the impacts on, and feedbacks from, the ocean as the result of a changing hydrological cycle?
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From page 47... ...
Advances in computational power and improvements in coding have allowed global oceanic GCMs to achieve sufficiently fine spatial resolution to begin to resolve mesoscale eddies. This convergence between "coarse scale" and "eddy resolving" oceanic models is similar to that occurring between "weather prediction" and "climate" models, as noted in the section "Physical-Chemical Interactions in the Atmosphere" (above)
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From page 48... ...
Interestingly, the addition of simple (though increasingly complex) biological-biogeochemical models into oceanic GCMs could allow for the study of possible biological changes under a forcing of changing climate and oceanic circulation fields.
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From page 49... ...
However, coupling oceanic and atmospheric models introduces new problems of unrealistic long-term drift and instabilities that are not exhibited by the uncoupled models. Further, adding biogeochemical processes to coupled oceanic-atmospheric GCMs is a prerequisite for complete description of the effect of carbon dioxide removed from the atmosphere by the ocean.
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From page 50... ...
an inadequate theoretical or observational understanding of certain key processes fundamental to the earth's coupled climate and biogeochemical subsystems and a corresponding and continuing uncertainty as to how best to incorporate or to parameterize them in oceanic GCMs and (2) a need for improved numerical methodologies (both prognostic and assimilative)
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From page 51... ...
to be crucial to the form and strength of the global circulation. Likewise, processes operating on the largest spatial scales have been termed "basin and global scale," and discussion of these shifts to a "top-down" focus.
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From page 52... ...
One example of the type of experiment necessary is the so-called Pacer release experiments, whose goal is to measure isopycnal and diapycnal mixing rates in the ocean. Limiting Processes: Mesoscales Over the past decade, much progress has been made in identifying and understanding several mesoscale processes that profoundly influence the oceanic circulation on either a regional or a global basis.
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From page 53... ...
Further study employing both models and observations is needed to define which processes can be reasonably treated through parameterization and which must be modeled explicitly. Limiting Processes: Basin and Global Scales The behavior of the global climate and biogeochemical systems is clearly tied to the nature, structure, and properties of the global oceanic circulation and primary production.
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From page 54... ...
Significant progress has been made in ENSO models, especially in terms of the coupling of atmospheric and oceanic dynamics (the TOGA program has been central in this development) , but the coupling between physical and biogeochemical processes such as new primary production and carbon dioxide exchange has not been modeled, although work is in progress.
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From page 55... ...
Research Priorities Fundamental oceanic processes important in the determination of the global biogeochemical cycles and the world's climate are poorly understood. Proper inclusion of these processes in models will require field programs tailored to understanding individual processes.
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From page 56... ...
Such error estimation will require synergy between the modeling effort and the field programs. In spite of these difficulties, the initial attempts at assimilating ocean color data into physical-biological models have shown that the accuracy of the model is improved, but that the improvement of the model diminishes after a short time.
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From page 57... ...
We need to better understand the sensitivity of the climate system to changing biogeochemical systems, and, if found to be relevant, biogeochemical systems must be included in our climate models. Including these relationships is expected to be computationally expensive, and yet ignoring the interaction of the physical-chemical-biological systems may lead to poor predictions of climatic change.
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From page 58... ...
Hence the development of the fully coupled models should be encouraged along two parallel paths: one to develop basin- and global-scale models with increasing levels of coupling and the second to develop a series of regional fine-scale models that could provide boundary conditions and parameterization tests for the larger-scale models. Each regional model could include the complexity and dynamics appropriate for simulating the processes in a specific region, and the necessity for maintaining interfaces with the larger-scale models would provide an overall consistent structure for model development.
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From page 59... ...
should be included when developing physical climate scenarios for use as forcing functions. The forcing functions given to the interface models will evolve as tested concepts from the interface models are incorporated into the earth system model, presumably modifying its predictions of whole-system response to changing greenhouse forcing.
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From page 60... ...
, trace gas biogeochemistry, · primary productivity and ecosystem carbon storage, and · vegetation composition and structure due to the changing macroclimatic forcing andlor atmospheric chemical composition. Critical tests of this model prior to its use in the predictive mode will be to · reproduce current patterns of biogenic trace gas and carbon exchange, using past and current climate as drivers; · reproduce key aspects of coupling between the paleoclimate and paleoecological records within regions of interest; · simulate contemporary spatial and seasonal patterns of vegetation properties, including primary productivity worldwide, using satellite indices as validation data; · capture patterns of ecological change along anthropogenically induced chemical gradients in the land component of this interface model; and · simulate surface fluxes of radiation, especially solar, and including spectral surface albedos in the atmospheric component of this interface model.
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From page 61... ...
Critical tests will include simulation of contemporary variations in global trace gas fields, especially of"integrator species" such as methyl chloroform and carbon monoxide; · methane and carbon dioxide concentrations and isotope ratios; large-scale tropospheric ozone features such as are observed in the tropics; · high-latitude stratospheric ozone; and exchange of water vapor between troposphere and stratosphere. Atmosphere-Ocean Subsystem For the interface model of the atmosphere-ocean subsystem, the challenge is to predict the responses of · water and energy exchange, · carbon dioxide exchange and carbon storage, · pattern of the spring bloom, and shifts in ecosystem composition and resultant shifts in oceanic mixedlayer chemistry (e.g., alkalinity)
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From page 62... ...
In addition to facilitating the analysis of the model output, such tools can play an important role in testing and debugging by allowing the modeler to see every time step of
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From page 63... ...
1986. SCOPE 29: The Greenhouse Effect, Climatic Change and Ecosystems.
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From page 64... ...
1984. Modeling terrestrial ecosystems and the global carbon cycle with shifts in carbon storage capacity by land use change.
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From page 65... ...
I Hydrological balance, canopy gas exchange, and primary production processes.
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From page 66... ...
Schimel (ads.) , Exchange of Trace Gas Between Terrestrial Ecosystems and the Atmosphere.
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