Volume One, Number One
Winter 1997

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The IGBP Task Force for Global Analysis, Interpretation and Modelling (GAIM) is in full swing. The initial years of GAIM have been devoted to developing the techniques which will be necessary for coupling Earth subsystem models to compile an integrated Earth system model. This has entailed the development of models of specific biogeochemical aspects of the Earth system as well as model intercomparisons for the purse of assessing model parameterization and performance. For this purpose, GAIM has been focusing on the Carbon cycle, begining with terrestrial systems, then incorporating marine as well. GAIM is now turning its attention to the pressing problems of model intercomparison, assessment, and integration.

A Few Words From the Executive Director

by Dork Sahagian


GAIM & IGBP

Since coming to IGBP, I have seen the growth and maturation of a truly remarkable international research organization. This is one which operates on a shoestring budget, is manned almost entirely by volunteers, and manages to transcend the traditional disciplinary research barriers to address questions regarding the Earth system that would have been otherwise impossible to treat. In the two years since the GAIM office was founded, the Task Force has come a long way toward establishing the research capabilities necessary for developing the models and understanding needed for construction of integrated biogeochemical Earth system models. Theinitial emphasis was on the terrestrial carbon cycle, expanding to include ocean carbon and now is growing to include the atmosphere as well.

It was a pleasure to see the seeds of IGBP program integration begin at the IGBP Congress last April. The enhanced interactions stemming from the Congress are laying the foundations upon which GAIMÕs role as the "glue" of IGBP will be built. Meanwhile GAIM will be working with the Core Projects in their efforts to develop subsystem models with the necessary linkages for coupling into integrated Earth system models. We would like to see integrated models as soon as possible, and indeed it would be possible to couple existing models at the present time to create such an Earth system model. However, it will be difficult to quantify its prognostic capabilities without knowing the sensitivities of the subsystem models to boundary conditions and fluxes. The question arises, as discussed at the GAIM Science Conference, "How robust must a subsystem model be before coupling it with others reduces the uncertainty of the coupled model to a level less than the individual uncertainties of the uncoupled component models?" It is not easy to address this question, but it suggests that we may now have subsystem models in the form of cards. We would like to develop them into bricks to avoid building an Earth system model in the form of a house of cards. As GAIM works with the Core projects, both by collaborative efforts as well as by intersection of membership, I believe that the answer to this and the many more specific questions which we now face will come to light.

I am looking forward to a bright future for GAIM, and IGBP in general, as we develop an ever strengthening research program directed at understanding the Earth system. Top


A Few Words From the Chair

by Berrien Moore III



Where have we been; where are we going?

Three linked themes are emerging in the study of global environmental change: 1) linkages and/or interfaces, 2) integrative experiments or important tests of our understanding, and 3) the interplay of simplicity with and against complexity.

At the IGBP Congress last April, we spoke about the key linkages: Land-atmosphere, ocean-atmosphere, land-ocean, and atmosphere physics with atmosphere chemistry. These subsystems have differing space and time scales (which themselves depend upon what is being used to determine system state), and consequently, they are often quite "stiff" as linked systems and therefore present difficulties in perturbation experiments. There are also widely varying degrees of parameterization with little understanding as to the effect(s) of the parameterizations.

Understanding global environmental change is not easy.

Understanding global environmental change is not impossible. Important linkage or integrative experiments and tests are NOW being done: a) the ocean carbon model inter-comparison project has linked atmosphere GCMÕs (mainly as drivers) with ocean GCMÕs containing carbon chemistry and crude biology; b) similarly, the terrestrial carbon models are being driven (partially) by GCM results; c) we are taking the preliminary steps with the GCM Atmosphere transport codes studies for tackling the chemistry connection; and d) we are beginning to tie together these three linked subsystems and consider tracers (CO2) as tests of the overall system understanding. Finally we are thinking about projects that involve measurements and modelling which link land systems (dynamic vegetation models, nutrient dynamics, soil moisture, and run-off) to drainage basin models (water flow and biochemistry in rivers) to GCM climate change drivers (initially one-way coupling using GCM results as drivers for very large drainage basins such as the Amazon). Within these macro-system experiments, we are beginning to understand the human drivers and, in time, the feedbacks. We are not mastering complexity, but neither are we shying away.

However, I believe that we need not shy away from simplicity either. We should consider a "re-exploitation" of simple models that consider the Earth system. The purpose would be threefold: a) to explore the dynamics that result from increasing the number of linked components, b) then to run a greater variety of forward calculations or tests, c) and finally, to provide tools for teaching (communicating ideas), both in the classroom and in the policy realm.

This could develop in several ways. Amongst them, I see:
1. Developing and comparing simple Earth System Models whose structure would raise difficult system dynamic issues such as chaos, multiple feedbacks with greatly differing time constants, parameterization sensitivities, etc., and

2. Collecting and documenting existing models of key features of the Earth system (e.g. Carbon Cycle) that could run on 486 class machines that would also be available over the World Wide Web.

GAIM has made and will continue to make extraordinary progress in exploring the complex linkages and/or interfaces within the Earth system, and we have mounted challenging integrative experiments and important tests of our understanding.

We need to begin now to think about the interplay of simplicity and complexity.

The issue of integration of subsystems into Earth system models is addressed in the last article in this newsletter.
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Global Wetland Distribution and Classification: Trace Gases and the Hydrologic Cycle
GAIM-DIS-BAHC-IGAC workshop

By Dork Sahagian, John Melack, and the participants in the IGBP Wetlands Workshop

The IGBP inter-element wetlands workshop involving GAIM, DIS, BAHC, IGAC, and LUCC, was held in Santa Barbara, California on May 16-20, 1996. The purpose of the workshop was to establish a functional parameterization of wetlands directed toward integrating wetland trace gas, hydrologic, nutrient, and other fluxes into regional and global biogeochemical models more effectively than presently possible. Wetlands scientists from every continent and various disciplines related to wetlands gathered and formulated a nine-parameter functional n-space into which all wetlands can be plotted. The formulation was directed jointly by field ecologists who helped define functions and by remote sensing specialists who helped determine the types of data sets which could be brought to bear on the problem of discrimination on a global basis between wetlands with different sets of parametric values. The initial nine parameters proposed by workshop participants were: Hydrology, Temperature, Primary production, Vegetation, Soil, Salinity, Chemical information, Transport of organics and sediment, and Topography/geomorphology. These may be subsequently refined to establish a robust set of orthogonal parameters.

The extent of wetlands is uncertain because there is no clear basis for identification and classification of wetlands on a global scale. In addition, the areal extent of wetlands is being modified as a result of land-use changes, so that once a globally consistent classification scheme is established, the areal distribution must be continuously monitored and recompiled.

New data are becoming available from remote sensing which provide a global perspective on wetland distribution and classification, but which are not yet reconciled with ground-based ecological and hydrological data. Further, there is a gulf between the scale of trace gas emissions as measured from the ground, and the measurable atmospheric effects of this based on remote sensing.

Global models of biogeochemical systems are dependent on an understanding of the exchanges of chemical components between the land, oceans, atmosphere, and biosphere. Wetlands are a particularly productive environment, yet the processes and fluxes of trace gas exchange with the atmosphere are only partly understood, and are only beginning to be measured on a global scale. For example, the methane budget is strongly affected by wetland sources, both natural and anthropogenic. Consequently, in order to correctly account for methane terms in global biogeochemical models, it is essential to understand the role of wetlands in methane production as well as the effect of changing wetland distribution.

Detailed maps of wetlands are available for the U.S. and Europe and regional maps are available for most of the world. However, these maps are almost always static and based on floristics rather than function. It would be beneficial to have current and ongoing monitoring of wetland extent and flooding, with classification based on biogeochemical function. Such information is now obtainable with remote sensing in conjunction with regional data on soils, climate, and vegetation. While some studies are addressing the global effect of atmospheric exchange of trace gases from wetlands, most have been concerned with wetlands at a local level.

Newly available remotely sensed data provides the opportunity for major advances in the classification of wetlands. Passive and active microwave remote sensing provides the capability of mapping inundation extent seasonally to monitor natural and anthropogenic variations. These are critical data because in many regions, the amplitude of natural seasonal variations are equal to or greater than the anthropogenic modifications. Independently, on the basis of SAR data, vegetation phenology can be determined.

Wetlands have been classified in various ways on the basis of hydrology, geomorphology, and vegetation. However, for the purpose of understanding the effects of wetlands on global biogeochemical cycles, it is necessary to devise a functional characterization of wetlands, so that distributions of wetlands can be included on this basis into global biogeochemical models. The primary mission of the IGBP Wetlands Workshop was to develop a scheme for functional characterization of wetlands.

The global areal extent of wetlands has been estimated as 5.3x1012 m2 [Matthews and Fung, 1987] or 8.6x1012 m2 [Mitchell, 1990], but these figures are uncertain. While relatively small compared to ocean, savanna, or forest area, wetlands are biogeochemically active because of their high productivity and redox gradients. In particular, wetlands are major natural sources of reduced gases such as methane and sulfur compounds, and can have high rates of denitrification and nitrogen fixation.

The timing and extent of flooding is the key environmental factor controlling ecological processes in wetlands. Flooding brings nutrients and creates the physical environment required by the plants and microbes. Hence, modifications to wetland hydrology severely disrupt their function. The U.S. and Europe have drained and converted wetlands extensively. Land use changes in developing countries are increasingly eliminating wetlands on a global basis. Moreover, given the expected increase in human population (mostly in developing regions) the pressure to convert wetlands for agriculture to meet growing food requirements is expected to increase even further. It has been estimated that the rate of wetland loss during the 19th and 20th centuries in the U.S. has been roughly 2.2x109 m2/yr [Mitchell, 1990; Mitsch and Gosselink, 1986], and has even influenced sea level as a result [Sahagian et al., 1994].

Once the existing wetlands data were reviewed at the workshop with the identification of data gaps, workshop participants evaluated appropriate techniques for generating new data sets including the use of remotely sensed data which can provide a synoptic perspective. There have been several remote sensing studies on characterizing various types of wetlands at differing scales using airborne and spaceborne systems. Most of these studies have been at a local scale using airborne systems. The challenge facing the workshop participants was to identify those techniques that can be applied to regional and global scales, yet provide the type and level of detail and information needed to compile and maintain an evolving wetland distribution inventory based on functional classification. Currently available optical and microwave systems need to be evaluated with respect to suitability of their spatial and temporal resolutions for generating new improved regional and global data sets on wetland extent and seasonality. A suite of different techniques and sensing systems may be needed to capture the necessary information.

Wetland processes

Wetland functions are defined as processes and manifestations of processes occurring in wetlands. Most functions fall within three categories: hydrologic, biogeochemcial and maintenance of habitat and food webs. Hydrologic functions include long and short-term surface water storage, and the maintenance of high water tables. Such functions reduce the amplitude of flooding peaks downstream, maintain base flow rates buffering flow distributions and maintain the hydrophytic community and habitat. Biogeochemical functions include the transformation and cycling of elements, retention and removal of dissolved substances from surface waters, and accumulation of peats and inorganic sediments. These functions retain nutrients and other elements, improve water quality, and affect aquatic and atmospheric chemistry. Biogeochemical processes such as methane production, sulfate reduction, denitrification, and iron reduction are driven by organic matter decomposition, while others such as detrital organic carbon and inorganic sediment storage are driven by sediment transport. Habitat and food web support includes maintenance of wetland plant communities which provide food and habitat for waterfowl and other animals, maintaining diversity.

Methane production is the terminal process of organic carbon remineralization in anoxic soils and sediments and occurs when there is a high input of labile organic matter in the absence of oxygen and alternative electron acceptors such as sulfate. Wetlands (including rice fields) are two of the largest sources of methane to the atmosphere due to the anoxic conditions occurring in their flooded soils and their high primary production. Together rice fields and natural wetlands make up about 40% of the methane input to the troposphere. The importance of northern wetlands in releasing methane to the atmosphere is still somewhat uncertain.

Wetland plants, including rice, serve to enhance methane emission by serving as conduits for gas exchange and through the production of root exudates and above and below ground litter. Important factors controlling methane production are salinity, fertilization of rice field soil, water level, temperature soil properties, light, and methane oxidation both at the soil water interface and in the rhizosphere. Comprehensive studies of several years duration have led some researchers to conclude that many of the factors influencing methane emission are not entirely independent and that integrating parameters or variables are required.



Wetland Functional Parameterization

There are several major biogeochemical constituents which are controlled by processes which occur in wetlands. Of these, carbon (CO2, CH4), sulfur (DNS, H2S) and nitrogen (in addition to water) have been chosen as the basis for developing a functional classification for wetlands. The flux of each of these is determined by several processes which act in all wetlands systems to varying degrees. Nine primary deterministic functions have been formulated so as to be independent of each other and represent all important biogeochemical functions of wetland ecosystems.

Workshop participants proposed an interactive classification scheme where one queries functionally based modeled or measured input parameters which could be displayed as contours. If, for example, one is interested in methane, the interaction of the input parameters could yield methane emission contours. Wetland functions (listed below) would be output responses determined by the input parameters (listed below). To validate the model compare model predicted function values with these determined observationally.

Wetland Functions

  1. Methane production
  2. Carbon accumulation or export
  3. Denitrification/N burial
  4. Sulfur cyclingÑ DMS, H2S production


These functions can be described by the following parameters:

  1. NPP Net Primary Productivity is determined by the difference between the amount of carbon incorporated into plant tissue and the amount of carbon respired.
  2. Temperature Temperature controls the rate of all processes, and in temperate and boreal regions freezing can arrest biogeochemical cycling seasonally.
  3. Hydrology Hydrology is critical in the function (and very definition) of a wetland. Key parameters that control hydrology are geomorphology, flooding, precipitation, and evapotranspiration. On the basis of hydrology, there are two categories of wetlands:
    1. Wetlands with stable water tables--water tables may move up and down relative to soil surface but these wetlands are always wet below. These wetlands have certain common characteristics including a reducing environment, little or no sediment input, soil formation is autochthonous, and peat formation (net carbon sinks). They can occur in northern climates, subtropical environments, or tropical environments. In these environments both CO2 uptake and methane emission are important.
    2. Wetlands that periodically dry out. These include floodplains and savannas. They have short-term accumulation of organic carbon but during drier periods this organic matter is decomposed, driving the cycles of S, Fe, N, and CH4. In this case, methane production is important but carbon deposition is not. It is important to differentiate between floodplains and deltas because the latter store carbon due to their persistent inundation.
  4. Organic matter and sediment transport Sediment and organic matter are transported in and out of a wetland by various processes including water flow, fire, grazing, harvesting, etc. These determine the availability and residence time of material to be processed (e.g. methane production or nitrogen cycling).
  5. Vegetation Vegetation is grouped in terms of vascular or non-vascular (see below), and affects the sites of production of organic matter. Non-vascular OM production must pass through a zone of aerobic decay as it transits to the methane production zone. Vascular plants are rooted in the methane production zone. Because the roots and thus exudate occurs within the methane production zone, there is more labile OM input to methanogens. When this effect is added to the vascular plant conduit effect through hollow stems, it further compounds the dominant role of vascular plant in methanogenesis.
  6. Chemistry Chemical information regarding organic materials (lignin, N content, DOC quantity, chlorophyll, etc.) is important in determining the conditions for reactions involved in methanogenesis, N cycling, etc. Changes in nutrient status may affect root biomass.
  7. Salinity Salinity influences the type of bacterial activity within a wetland and thus the production of methane, carbon accumulation, and S & N cycling.
  8. Soils The type of soil present in a wetland can be characterized by texture, C content, and nutrient status.
  9. Topography/Geomorphology The surface topography and geomorphologic structure of the regions surrounding the wetland controls the large-scale hydrologic behavior as well as vegetation characteristics.

Anthropogenic Factors

The area of wetlands is subject to change as a result of both natural and anthropogenic factors. The conversion of wetlands for agriculture and urban development leads to major changes in hydrology, vegetation, soil characteristics, and concomitant biogeochemical cycles. Wetland areas are influenced both by these on-site factors (e.g. impoundments and drainage) and by off-site or upland areas where clearing may lead to enhanced run-off, erosion, sedimentation, and accumulation of organic and inorganic solutes and particulates. From the perspective of land use, wetlands are important as a direct source of food and various other products (e.g. lumber), grazing grounds, and drinking and irrigation water sources. Uplands surrounding wetlands need to be taken into account because of their controls on hydrology (through dams) and nutrient supply (through fertilizer use) which affect wetlands. Conversely, the landward encroachment of coastal wetlands resulting from recent and future sea level rise may threaten developed and agricultural coastal regions.

One could argue that the single most important factor affecting wetland distribution changes in the future will be demographic pressure, and related agricultural and urban land use. This factor may well dwarf some of the expected changes in sea level, temperature and CO2 concentration variations.

In estimates of the extent and distribution of wetlands, confusion results in cases where man has altered either the hydrology or organic/inorganic flux. These changes lead to the transformation of wetlands in diverse directions with concomitant effects on biogeochemical cycles. Human intervention may have four major effects on hydrologic fluxes:

  1. Total drainage and transformation of wetlands into grasslands and/or dry cropland and urbanization. Hence the area is technically excluded from wetland inventories. It is necessary determine the areal extent of altered wetlands so that the influence of human activity can be assessed.
  2. Partial water management for the purpose of reducing the frequency and extent of flooding (e.g. summer dikes, lowering of water table) either for fishing or agricultural purposes. By definition, these areas remain wetlands, but effects on biogeochemical cycles depends strongly upon flooding regime as well as additions of organic and inorganic carbon. In addition, carbon can be removed in massive quantities through grazing and peat harvesting.
  3. Total hydrologic control for the purpose of rice production. This leads to changes in the fluxes of methane, CO2, N, P, K, S, etc.
  4. Grazing without hydrologic control resulting in changes in vegetation and consequent changes in carbon and N balances. This area remains a wetland, but is functionally altered.

REFERENCES

Matthews, E., and I. Fung, Methane emission from natural wetlands: Global distribution, area, and environmental characteristics of sources, Glob. Biogeochem. Cycles, 1, 61-86, 1987.

Mitchell, G.J., Foreward to Wetland creation and restoration, in Wetland creation and restoration: The status of the science, edited by J. Kusler, and M. Kentula, pp. ix-x, Island Press, Washington D.C., 1990.

Mitsch, W., and J. Gosselink, Wetlands, 539 pp., Van Nostrand Reinhold, N.Y., 1986.

Sahagian, D.L., D.K. Jacobs, and F.W. Schwartz, Direct anthropogenic contributions to sea level rise in the twentieth century, Nature, 367, 54-56, 1994.


Participants in the IGBP Wetlands Workshop- May, 1996. Standing from left to right; Dork Sahagian, Brad Newton, Leal Mertes, Charon Birkett, Kevin Rogers, Tom Dunne, John Melack, Jeff Chanton, Laura Hess, Leslie Morrissey, Louise Fresco, Elaine Matthews, Ron Sass, Yoshifumi Yasuoka, Max Finlayson, Wolfgang Junk, Victor Klemas, Reyaldo Victoria, Misauki Tamura, Nigel Roulet, Suzanne Sippel, Mats Nilsson. Seated from right to left, Brij Gopal, the late Ted Hollis (with official wetland rubber boots). Not photographed, Ichtiaque Rasool, Jack Estes.


Ted Hollis, seated in the photo holding rubber boots, died this Fall. He is holding rubber boots in the photo to emphasize the point that however grand and sophisticated our remote sensing techniques become, we will still need people wearing rubber boots and slogging about through wetlands in order to provide the necessary ground truth calibration and validation data. We will miss Ted and his insights- his death is a great loss for the wetlands research community. He was a good colleague and good friend. Top




GAIM Science Conference

By Dork Sahagian and Berrien Moore III

The First GAIM Science Conference was held on Sept. 24-29, 1995 in Garmisch-Partenkirchen, Germany, and consisted of 5 days of oral and poster sessions. The goal of the Science Conference was to provide a venue for the dissemination of preliminary results for the purpose of steering subsequent research efforts toward reliable prognostic biogeochemical models. The Science Conference focused on papers in the areas of global data analysis and assessment, modelling of biogeochemical systems and their relationship to physical climate and hydrologic systems, and interpretation of current trends as indicated by global databases and model results for extrapolation with regard to future Global Change. Oral and poster session topics were grouped by time periods, including "Paleo" (A limited number of hard-copy abstract volumes are available from the GAIM Office. The conference was co-sponsored by the German National IGBP Secretariat in Berlin, and supported by NSF, ISF, German National IGBP, START, ENRICH, and the German Development Foundation, with GAIM support provided by the USEPA.

A brief synopsis appears in the following boxes. The next GAIM Science Conference is planned for 2000.
MON. - The "Paleo" Era
The concern with future Earth system responses to large perturbations in atmospheric composition and climate makes it important to exploit the recent geological record as studied by the IGBP project Past Global Changes (PAGES). The paleo record in fact provides the only means to test such models under conditions (in the past) that are as different from present as the conditions expected to apply in 50-200 yearsÕ time.
WEDS. P.M. - Integrating the Developing World in Global Change Modelling
A special session focused on the concerns of developing countries was held on Wednesday afternoon. GAIM recognizes the importance of linking regional research programs into the global research questions on which it focuses. Moreover, there is a growing realization of the importance of tropical and subtropical regions in the study of global environmental changes and data requirements to global change issues. The success of GAIM depends on gathering expertise as well as data from the entire planet.

Current modelling results were discussed as well as future global data needs to encourage collaboration and involvement with ongoing international modelling efforts. In addition, many issues emerged which served to better identify the resource and other needs of scientists from developing countries. It is clear that these needs must be fulfilled so that they can more effectively gather, assess, and integrate global change data from their regions. In many countries, leading sicentists do not have even the most basic computation or communication facilities which would make involvement in international global change research programs feasible. The session included an open discussion of links between issues of local scientific interest in developing countries and global scientific issues, and resource requirements and funding mechanisms for enhancement of global change research in developing countries. The discussion at this session led in part to the planning of the African-GAIM Modelling Workshop.

TUES. - The Historical Era
The historical era (2 concentration. At present, however, we are unable, by accounting for other sources and the redistribution of carbon within its global cycle, to relate observed increases to estimates of past fossil fuel emissions. This questions the veracity of estimates of future CO2 increase and drives a substantial effort to understand carbon cycle responses to human activities over the past several centuries. The causes since the industrial revolution of increases in other greenhouse gases such as CH4 and N2O are less certain, primarily because changes in the distributions and magnitudes of their sources are poorly known.
WEDS. A.M. - Global Systems Integration
This special session departed from the temporal sequence structure of the conference, and focused on the interactions and feedbacks between biogeochemical subsystems (e.g. atmosphere, ocean, terrestrial ecosystems, etc.) and integration into whole-Earth models.
FRI. - The Future
The purpose of the "Future" session of the science conference was to bring forth preliminary results and discussion of prognostic biogeochemical models. The capability of biogeochemical models to predict future changes in the Earth system is dependent on the understanding of past global changes. For instance, by comparing "contemporary" rates of change to those of older and longer time periods, prognostic models may more accurately predict magnitudes of change in Earth systems and subsystems. While prognostic biogeochemical models are presently in a very primitive stage of development, comparison of the models will lead to better identification of data needs, shortcomings in our understanding of rates and interactions between changing subsystem components, and sensitivities of models to uncertainties in each subsystem component as well as component interactions.
THURS. - The Contemporary Era
The Contemporary Era (the period from immediate past to immediate future) provides the greatest availability of data over the immediate past and the easiest task of validation over the immediate future. Further, now is a time of rapid change, representing the most rapid change available to study over the last millennium. The session highlighted papers directed at the global budgeting and modelling of the present-day state of the major biogeochemical cycles.

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Ocean Carbon-Cycle Models: Exploring the differences

By Jim Orr

How and why do predictions from 3-D ocean carbon-cycle models differ? This question is the seed from which has grown the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP). Initiated by IGBP/GAIM in 1995, its main goal is to help improve manÕs understanding of the ocean as the major long-term depository of CO2.

During the first year of comparison, OCMIPÕs focus has been to pinpoint differences between simulations of both natural and anthropogenic CO2 in four 3-D models: Max Planck Institut fur Meteorologie (MPIM, Germany), Princeton University/GFDL (USA), Hadley Centre (U.K. Met. Office), and IPSL/CFR-LMCE-LODyC (France). Additionally, OCMIP has compared measured vs. simulated C-14 (both the natural and bomb components, separately) as a means to validate the model circulation fields which drive each of the four carbon-cycle models.

In general, model predictions vary considerably. Although models agree to within +/- 20% for global uptake of anthropogenic CO2 during the 1980Õs, regional uptake can differ by much more (Figure 1). For example in the vast Southern Ocean, where surface waters communicate readily with the deep ocean and where all models absorb the majority of anthropogenic CO2, models disagree by more than 100% as to how much is absorbed. A related difference in the same region is the predicted position of maximum uptake, which varies by 20 degrees N-S between models. For natural CO2, simulations likewise differ most in the Southern Ocean. To address these differences, model validation with tracer data is vital.

Evaluation of deep-ocean circulation fields with the natural component of C-14 reveals that in the Pacific all four models produce distributions that are reasonably close to that observed; however, certain problems are apparent, e.g., all models under-predict the along-bottom, northward penetration of Antarctic Bottom Water (AABW). The Atlantic proves more difficult to get right. It remains a challenge to achieve the observed balance between filling of the deep North Atlantic with water from the north (NADW) and infiltration of AABW from the south. Validation of the near surface circulation with bomb C-14 also reveals model differences that appear most pronounced in the Southern Ocean. Unfortunately, few data are available there, a situation that will improve once the WOCE C-14 dataset becomes available. On the other hand, GEOSECS data is adequate in the northern subtropical gyres to diagnose that two of the models exhibit partial remedies to the classic inability to reproduce the observed west-to-east gradient in the bomb C-14 inventory (Figure 2). Ameliorations appear to derive from explicitly including formulations for mixing in the mixed layer and along surfaces of constant density. Better parameterizations for the role of sub-grid scale eddies would probably also help.

Future OCMIP simulations will remain focused on natural and anthropogenic CO2, but for added insight we will employ additional tracers as well. Comparison with present-day measurements demands that modelers simulate both natural and anthropogenic CO2. Moreover, a proper understanding of the preindustrial carbon cycle is prerequisite to understanding changes that have and will take place. OCMIP will also begin to explore details of the relationships between CO2 and two biogenic tracers: O2 and C-13. Both are now being used to help diagnose oceanic uptake of anthropogenic CO2. Their relationships with CO2 vary, however, between the different OCMIP models. Another facet of upcoming OCMIP efforts will take a more in-depth look at modeled ocean circulation fields, through the eyes of additional circulation tracers. Differences in model-predicted circulation fields are largely responsible for discrepancies between OCMIP simulations of the carbon cycle. OCMIP will validate simulated circulation fields by making runs for CFCÕs (inert transient tracers for which many oceanic measurements are now becoming available). Also, numerical tracer simulations will be made as a means to better understand the role of the Southern Ocean in the global ocean carbon cycle.

The long range objective of OCMIP is to improve manÕs understanding of the oceanÕs carbon cycle and the crucial role of its major controlÑocean circulation. Such critical information will help policymakers make informed decisions concerning future increases in atmospheric CO2 and climate change.
View figure: Air-sea CO2 flux
View figure: Bomb CO2 Inventory

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GLOBAL NET PRIMARY PRODUCTIVITY: A MODEL INTERCOMPARISON

By Wolfgang Cramer, Berrien Moore III, and Dork Sahagian

Global primary production of ecosystems on land and in the oceans is a crucial component of biogeochemical model development within IGBP. As key components in the terrestrial carbon cycle, geographically referenced net primary productivity (NPP) and gross primary productivity (GPP) and their corresponding seasonal variation are needed to enhance understanding of both the function of living ecosystems and also their effects on the environment. Productivity is also a key variable for the sustainability of human use of the biosphere by, for example, agriculture and forestry. Recently, it has become possible to investigate the magnitude and geographical distribution of these processes on a global scale by a combination of ecosystem process modelling and monitoring by remote sensing. Since agricultural and forestry production provide the principal food and fuel resources for the world, monitoring and modelling of biospheric primary production are important to support global economic and political policy making.

For estimates of the global carbon balance, a large amount of uncertainty centers on the role of terrestrial ecosystems. Geographically referenced gross primary productivity (GPP), net primary productivity (NPP), and heterotrophic respiration (Rh) and their corresponding seasonal variation are key components in the terrestrial carbon cycle. At least two factors govern the level of terrestrial carbon storage. First and most obvious is the anthropogenic alteration of the EarthÕs surface, such as through the conversion of forest to agriculture, which can result in a net release of CO2 to the atmosphere. Second, and more subtle, are the possible changes in net ecosystem production (and hence carbon storage) resulting from changes in atmospheric CO2, other global biogeochemical cycles, and/or the physical climate system. The significant influence of the terrestrial biosphere on the global carbon balance and hence on the problem of climate change has become more widely recognized during the past two decades, and now the role of terrestrial ecosystems is recognized to be central to the residence time of carbon dioxide in the atmosphere.

To understand the present and to predict the future role of ecosystems in this global context, observations, while necessary, are hardly sufficient, and a range of global terrestrial ecosystem models which capture the critical processes in the biosphere are needed. Several such models now exist, others are in various stages of development, and it has become possible to investigate the magnitude and geographical distribution of primary productivity on a global scale by a combination of ecosystem process modelling and monitoring by remote sensing. Biospheric flux models all somehow (explicitly or implicitly) relate geographically specific and comprehensive estimates of temperature, water availability and photosynthetically active radiation (PAR), as well as their seasonal changes, to the some or all of the basic processes of photosynthesis, growth and maintenance respiration, water and nitrogen fluxes, allocation of photosynthates in the plant and the production and decomposition of litter.

One of the early results that emerged from the first of a series of NPP model intercomparison workshops, Potsdam Õ94, was that a major reason for differences between outputs of the same variable between different models was that the input data for the same variable were from different sources and carried different uncertainties (this was true for both ground-based observations such as climatic data and for remote sensing data such as AVHRR-derived NDVI). Consequently, many of these data were standardized for the second workshop, "Potsdam '95." The scientific sponsorship of this workshop was jointly by GAIM, DIS, and GCTE, and it was hosted by the Potsdam Institute of Climate Impact Research (PIK), with financial support from NASA, the European Commission, and the U.S. Environmental Protection Agency. The purpose of Potsdam '95, like Potsdam Õ94 was to support a series of model intercomparisons by the various modelling teams around the globe that are currently modelling the terrestrial biosphere at large scales. There are significant differences in the calculation of NPP within current global terrestrial models, and Potsdam '95 was held in order to compare model parameters and outputs. Another NPP workshop is being planned for 1997, but with a more focussed scope. Now that some of the causes of model ouput differences have come to light, it is possible to address some specific issues such as the transient response of model outputs to perturbations introduced by land use changes and other system alterations.

A fundamental problem of such comparisons is that the target variable, net biospheric carbon flux, cannot be measured at the appropriate spatial scale for any significant part of the globe. Direct validation of any of the models therefore is therefore impossible, although several indirect validation methods exist. A third limitation concerns the quality of the existing observation data sets. For climate, a range of efforts have been made to improve available data sets for the application of biospheric models (including a May, 1996 GCTE/GAIM workshop on that topic). However, climate is only one significant variable; another one (for potential vegetation) is soils, regarding which several activities are currently underway. The two most crucial gaps exist in the area of historical changes in global land use, which is clearly a significant element in the worldÕs carbon balance, and in the compilation of point-based observations of biospheric fluxes.

A comprehensive data strategy for the models at the heart of the terrestrial component of the IGBP, the atmosphere-biosphere interaction models, is still lacking. The NPP model intercomparison has made it clear that existing data must be chosen and used in a standardized way if like models are to be compared, and ultimately, if complementary models are to coupled. It has also clarified data gaps which can now be filled before models can reliably simulate the role of terrestrial ecosystems in the global carbon cycle. However, it is not necessary for model development to wait until all gaps in the global observing systems are closed. Rather, IGBP can take the lead in coordinating existing and future data sources in a way that will optimize their utility throughout the global change research community.

At Potsdam '95, models were compared on the basis of two primary salient criteria:

Some key issues arose on the basis of the model intercomparisons:

In addition to comparing model results, the workshop participants assembled and compared an extensive number of input datasets during and after Potsdam Õ94. The standard data sets included climate, soil texture, solar radiation, and a weather generator. This intercomparison of input data set the stage for a set of "Standard Experiments" which were a new contribution of Potsdam '95. In this exercise, there was a standard data base for temperature, precipitation, solar irradiance and soil texture, a weather generator, AVHRR, and NDVI. Differences still existed in vegetation cover, LAI, and the parameterization of the models for processes such as decomposition, nutrient cycling, and evapotranspiration.

During and after Potsdam '95, NPP was investigated at the global, regional and biome level. These results formed the basis for a poster presented at the GAIM Science Conference. At the global level, a map of global NPP mean of all models was generated. In addition, the standard deviation for all models was mapped, and a table of the global NPP value predicted by each model was created.

At the Regional level, a monthly series of maps for each model was generated. The regional analysis highlights the seasonal sensitivity of NPP and the related differences between NPP models.

At the Biome level, a series of plots was generated of average model NPP vs. climate drivers (temperature and precipitation). It was found that different models are based on different definitions of biomes and steps are being taken to construct a standard set of biomes independent of model appliction.

Models used in the Potsdam '95 comparison included:
Biome-BGC, Biome2, CARAIB, CASA, CENTURY, DOLY, FBM, GLO-PEM, HRBM, HYBRID, PLAI, SDBM, SIB, SDBM, SILVAN, TEM, AND TURC.

Participants in Potsdam '95 included:
G. Churkina, G. Colinet, J. Collatz, W. Cramer, W. Emanuel, G. Esser, C. Field, A. Fischer, A. Friend, A. Haxeltine, M. Heimann, J.Hoffstadt, C. Justice, J. Kaduk, L. Kergoat, D. Kicklighter, W. Knorr, G. Kohlmaier, B. Lurin, P. Maisongrande, P. Martin, R. McKeown, B. Meeson, B. Moore, R. Olson, R. Otto, W. Parton, M. Pleochl, S. Prince, J. Randerson, B. Rizzo, A. Ruimy, S. Running, D. Sahagian, B. Saugier, A. Schloss, J. Scurlock, W. Steffen, P. Warnant, U. Wittenberg

The next NPP workshop is being planned as a tightly focussed comparison of results aimed at assessing modelled NPP transient response to perturbations, both natural and anthropogenic. Date and venue are not yet finalized.

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Regional Interaction of Climate and Ecosystems

by Catherine Ciret and Ann Henderson-Sellers

The activities of the RICE project have been mainly in three areas: (i) ascertaining the effects of climate and soils on climate simulated by global models, (ii) establishing the sensitivity of terrestrial vegetation models to the climates simulated by global climate models (GCMs) and (iii) facilitating the integration of new vegetation schemes into coupled global models.

A recent focus of the RICE project was to assess the uncertainties in the prediction of vegetation using climate model output (cf. ii). Although GCMs and vegetation models have been widely used in the assessment of climatic impacts on ecological systems, it is commonly admitted that there remain large uncertainties in the GCM predictions. Specifically, climate predictions are often inaccurate at the regional level. Hence, the use of climate models in the estimation of the impact of climatic change on global and regional ecosystems remains highly problematic.

In order to evaluate the reliability of climate models with respect to ecosystem modelling, two global equilibrium vegetation models, BIOME1 [Prentice et al., 1992] and a version of the Holdridge scheme [Holdridge, 1967] were used in conjunction with several climate model experiments from the Model Evaluation Consortium for Climate Evaluation (MECCA) project [Henderson-Sellers et al., 1995]. The aim was to identify which regions and simulated ecosystems were sensitive to the biases of the climate simulations.

In the research reported here [Ciret and Henderson-Sellers, 1996] the GCMs and global vegetation models are linked in a one way mode (i.e. no feedback from the vegetation model to the GCM is allowed). The approach consists of comparing the vegetation distributions predicted by the two vegetation models using simulated climates against the vegetation distributions predicted using observed climate. The spatial resolutions of the different maps of vegetation had to be identical to enable this comparison, and it was decided to aggregate spatially the observed climatology to the resolution of the GCMs.

The results indicate that the overall performance of coarse resolution climate models with respect to vegetation prediction is rather poor (see Figure 1). The discrepancies between vegetation distributions computed from observed and simulated climatologies represent more than 50% of land area. The comparison of vegetation distributions shows that there are some common tendencies amongst the GCMs used in this study to induce the overprediction or underprediction of certain biomes. For example: the biomes belonging to dry climate regions are underpredicted, and the woodlands (i.e. xerophytic woods/shrub) and temperate/cold forests are overpredicted.

The climatic variables responsible for the discrepancies between vegetation predictions are identified for each individual vegetation type. The differences in vegetation predictions are overall due to the overestimation of the soil moisture index and precipitation, to the overestimation of growing degree days and to the underestimation of the annual minimum temperatures. Certain biomes appear to be particularly sensitive to the biases in the simulated climates (e.g. grassland, xerophytic woods). Overall, the discrepancies in vegetation predictions are predominantly due to biases in the simulation of the hydrology (i.e. soil moisture index and total annual precipitation) and these results indicate that the uncertainties in the simulation of the soil moisture availability should be carefully evaluated before a high degree of confidence can be vested in the prediction of vegetation, and moreover in the prediction of vegetation change.

Most of the GCMs used in this study have a coarse resolution (i.e. 4.5û lat by 7.5û lon). However several studies have shown that some features of the climate simulations can be improved by increasing the horizontal resolution of the climate model [Boville, 1991; Gleckler and Taylor, 1993; Kiehl and Williamson, 1991], hence leading to a more realistic prediction of vegetation distribution [Claussen and Esch, 1994]. Therefore the sensitivity of the vegetation models to changes in the spatial horizontal resolution of the GCM CCM2 was also investigated [Ciret, 1996]. The climate integrations come from a set of experiments undertaken by Williamson et al. [Williamson et al., 1995] in which the GCM CCM2 was run with increasing spatial resolutions (from 4.5û lat by 7.5û lon to 1.9û lat by 1.9û lon). The observed climate was aggregated to match the various resolutions of CCM2.

The global scale vegetation prediction was found to be improved when using higher resolution climate simulations. However the best results are not necessarily obtained with the highest resolution (cf. findings) [Williamson et al., 1995]: for instance a more "realistic" vegetation distribution was obtained with the BIOME model using the T42 climate integration instead of the T63 climate integration (i.e. 2.8 lat by 2.8 lon versus 1.9 lat by 1.9 lon). The improvement in the biome prediction was found to be very uneven. The biomes for which the distribution have been largely improved with increasing resolution are the hot desert, tundra and certain forests types.

In summary, this research has shown that the prediction of biomes using simulated climatologies is not yet fully satisfactory. It is nevertheless possible to increase our level of confidence in the prediction of vegetation by carefully evaluating the performance of the vegetation models driven by simulated climatologies and by identifying the causes of the biases.

Another recent focus of the RICE project has been to investigate the possibility of introducing some aspects of the ecosystem dynamics into the modelled climate system (cf. i). The interactions between vegetation and atmosphere are a key issue in climate system modelling, however the vegetation characteristics represented currently in the soil-vegetation-atmosphere transfer schemes (SVAT) are often prescribed and are not yet allowed to fully respond to the climate forcing. The work undertaken in collaboration with Professor Katia Laval, Dr Jan Polcher from the "Laboratoire de Meteorologie Dynamique" (LMD) and Dr Xavier Le Roux from the "Institut National de Recherches Agronomiques" (INRA), aimed at assessing whether some aspects of the dynamics of vegetation can be simulated in the land-surface scheme SECHIBA [Ducoudre et al., 1993]. One important vegetation parameter is the Leaf Area Index (LAI) since it is usually involved in the calculation of both the canopy transpiration and the evaporation of foliage water. It was decided to try to simulate the seasonal variation of LAI in one of the GCM LMD6 grid cell. The approach consists of using a plant primary productivity and phenology model [Roux, 1996 in press] developed and calibrated according to the conditions found in the Lamto Scientific Site, Western Africa, where the dominant ecosystem is humid savanna.

The model was modified and simplified, and forced with a 10 years climate simulation from the GCM LMD6. The seasonal variations of the simulated LAI appear to be relatively realistic, despite the fact that the LAI is overall underestimated, and the start of the growth phase is delayed due to insufficient simulated soil water content. Further work needs to be done to evaluate whether the various functions of the model and the values of the parameters could be generalised to other types of savannas (e.g. Australian savannas). If the method employed to simulate the plant phenology in this region was found to be applicable to other savanna types, this approach would enable the LAI to be simulated daily as a function of GCM climate variables in the grid cells where the dominant vegetation is savanna.

Figure 1: Biome distributions simulated by the BIOME1 model using the control climates from the GCMs (a) CCM1Oz, (b) CCM1, (c) CCM0, (d) CCM1W, (e) CCM2 at R15 resolution, (f) BMRC and (g) the observed climate from Legates and Willmott (1990) and ISCCP (1992).

REFERENCES

Boville, B., Sensitivity of simulated climate to model resolution, J. Climate, 4, 469-485, 1991.

Ciret, C., Impacts of increasing the spatial resolution of the climate model CCM2 on the simulation of natural ecosystems, Submitted Clim. Dyn., 1996. Ciret, C., and A. Henderson-Sellers, Sensitivities of global vegetation models to present-day climates simulated by global climate models, Glob. Biogeochem. Cycles, submitted, 1996.

Claussen, M., and M. Esch, Biomes computed from simulated climatologies, Clim. Dyn., 9, 235-243, 1994.

Ducoudre, N., K. Laval, and A. Perrier, Sechiba, a new set of parameterizations of the hydrologic exchanges at the land-atmosphere interface within the LMD Atmospheric General Circulation Model, J. Climate, 6, 248-273, 1993.

Gleckler, P., and K. Taylor, The effect of horizontal resolution on ocean surface heat fluxes in the ECMWF model, Clim. Dyn., 9, 17-32, 1993. Henderson-Sellers, A., W. Howe, and K. Mcguffie, The MECCA Analysis Project, Glob. and Planet. Change, 10, 3-21, 1995.

Holdridge, L., Life Zone Ecology, Tropical Science Center, San Jose, 1967. Kiehl, J., and D. Williamson, Dependence of cloud amount on horizontal resolution in the National Center for Atmospheric Research Community Climate Model, JGR, 96, 10955-10980, 1991.

Prentice, I.C., W. Cramer, S. Harrison, R. Leemans, and others, A global biome model based on plant physiology and dominance, soil properties and climate, J. Biogeogr., 19, 117-134, 1992.

Roux, X.L., Modelling the savanna radiation balance, water balance and primary production, in Lamto, a savanna ecosystem., in Thirty years of ecological studies in West Africa, edited by J.-C. Menaut, L. Abbadie, and M. Lepage, Springer Verlag, Ecological Studies, 1996 in press.

Williamson, D., J. Kiehl, and J. Hack, Climate sensitivity of the NCAR Community Climate Model (CCM2) to horizontal resolution, Clim. Dyn., 11, 377-397, 1995.

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PALEOTRACE GAS CHALLENGE:

Unraveling natural variability and linkages of trace-gases and climate over the last 150 ky

By Colin Prentice and Berrien Moore

A new joint GAIM-PAGES-IGAC effort plans to focus research on defining the causes of the observed atmospheric composition changes over the last 150 ky, and in particular the roles of the terrestrial biosphere and oceans in generating these changes. This effort will involve close interaction between the modelling communities of GAIM (e.g. modelling of trace gas sources and sinks in the biosphere), PAGES (e.g. information from ice cores and other records of past atmospheric conditions), and IGAC (e.g. trace gas transport and chemical interactions in the atmosphere). The Paleo trace gas "challenge" is based on unraveling the natural variability and linkages of trace-gases and climate over the last 150 ky. Natural atmospheric trace-gas concentrations and climatic change are clearly linked, but the full extent of these linkages have yet to be fully understood. In seeking to measure improvements in our understanding, we can test our models against the historic record, recognizing that there are differences between past and future change. Emphasis will be placed on the use of time-dependent, coupled climate system models, and in producing models that are capable of simulating all aspects of the observed record of change. GAIM will work with PAGES and IGAC to develop the observational framework needed on the basis of "paleo" data, including records of oceanographic (e.g., physical, biological, and chemical), terrestrial (e.g., vegetation and soils), cryospheric (e.g., ice sheet and sea ice), and atmospheric (e.g., trace-gas) changes. A specific result of the proposed project will be an improved ability to anticipate future natural and anthropogenic trace-gas and climatic changes.

An important test, for example, is to explain the co-evolution of climate and atmospheric carbon change over the last 150 kyrs. Data from ice-cores demonstrate that atmospheric CO2 and CH4 concentrations changed dramatically, and at times abruptly, over this period of interglacial-glacial-interglacial climatic change. These changes included millennial-scale changes, as well as significant decade- to century-scale change in atmospheric carbon and climate. However, the exact climate system mechanisms behind these observed changes have not been elucidated. In particular, an understanding of the mechanisms of the slow decrease followed by rapid increase in CO2 concentrations in the last 150 kyrs may shed light on important biogeochemical systems and their coupling with the physical climate system. A preliminary discussion of this problem began at the recent GAIM Science Conference, where it was suggested that it was important to understand the events during the transitions from the last glacial to the present interglacial and from the last interglacial to the last glacial, because of the strong variations of the entire Earth system, as reflected in the biogeochemical parameters.

Paleo-parameters are generally not identical with the parameters measured in monitoring networks and used in model experiments. Consequently, it is critical to understand the relationships between available observational data/measurements and the quantities of interest in global biogeochemical models. Transformation of proxy information into model parameters is normally accomplished through transfer functions. The importance of proxy-information for Global Change science is often underestimated because of the difficulty in converting them into the standard physical and chemical parameters. On the other hand, the proxy information reflects the actual regional and local impact of extreme weather events and of climate change in the past and thus gives indications regarding potential future impacts, in which we are ultimately interested.

The outline of a strategy to address the major issues in the "challenge" emerged at the IGBP Congress in April, 1996. The strategy is based on two complementary approaches commonly used in Quaternary science "time slice" and "time series". These approaches are currently pursued separately, both by data specialists and by modellers.

The time slice approach is typified by BIOME 6000: data are gathered for a particular period (which must be fairly "thick" e.g. often ± 500 yr) because of dating control problems, the emphasis being on spatial resolution, and on establishing generalized spatial patterns in variables that are very extensively measured. These patterns can then be compared with "snapshot" simula- tions using full three-dimensional models, with slowly varying boundary conditions (e.g. orbital conditions, ice-sheet extents and heights) specified. The time slice approach was adopted by CLIMAP for sea-surface conditions, extended to the terrestrial realm by COHMAP, and is currently being pursued further by TEMPO and PMIP/PMAP. The approach has led to major advances in our understanding of the processes determining the broad outlines of regional to continental scale changes in climate on glacial-interglacial time scales.

The time series approach instead focuses on high-resolution temporal studies, often including more esoteric signals, either of global quantities (such as atmospheric CO2 concentration) or of more local signals. Such studies are epitomized by ice-core, tree ring, and coral research, but similar tactics are increasingly being adopted in marine and terrestrial sedimentary investigations. The modelling counterpart is the development of "2 1/2- dimensional" models which include highly simplified representations of the oceanic and atmospheric circulations, in order to introduce the possibility of interactively modelling the dynamics of sluggish parts of the system such as ice sheets and crustal deformation. The time series approach has yielded major advances in the last five years with regard to Dansgaard-Oeschger events, Bond cycles and Heinrich events as well as the recognition of considerable fine structure in the climate of the present interglacial. Time-dependent models also have contributed to our understanding of the factors that may be involved in pacing the glacial-interglacial cycles, and most recently also the nature of the oscillations in the thermohaline circulation under different freshwater flux regimes (glacial vs. interglacial).

"The more you know, the more you know you don't know"

Some key areas in the time slice approach are as follows:

Key areas in the time series approach include:

We plan to initiate the project with a workshop focused on defining the state-of-the-art, and on planning the GAIM-PAGES-IGAC collaboration in the project. The initial plans for the workshop were formulated together with PAGES and IGAC at the IGBP Congress in Germany in April, 1996. Several specific questions were defined in preparation for the proposed workshop. These include, but are not limilted to:

Discussion of the above issues will set the stage for understanding the causes and consequences trace gas evolution, both in terms of magnitudes, rates, and signs of concentration changes.

References

Cao, M., S. Marshall, and K. Gregson, Global carbon exchange and methane emissions from natural wetlands: application of a process-based model, J. Geophys. Res., 101, 14399-14414, 1996.

Chapellaz, J.A., I.Y. Fung, and A.M. Thompson, The atmospheric CH4 increase since the last glacial maximum: 1. Source estimates, Tellus, 45B, 228-241, 1993.

Frolking, S., and P. Crill, Climate controls on temporal variability of methane flux from a poor fen in southeastern New Hampshire: measurement and modelling, Glob. Biogeochem. Cycles, 8, 385-397, 1994.

"Often in the end, when all is said and done, there was more said than done"

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African-GAIM Modelling Workshop

By Dork Sahagian and Berrien Moore III

GAIM in close collaboration with BAHC, GCTE, LUCC, and START is planning to hold a workshop for the purpose of integrating the African Global Change modelling community into the GAIM effort. The workshop will be held in Kenya on March 3-12, 1997. The workshop is aimed at incorporating the knowledge of regional African experts in ecosystems, hydrology, and land use into global models. Modelling capacity within the African scientific community will also be strengthened and thus further support ongoing research efforts such as the Miombo network and Kalahari transect.

The global environmental issues that the IGBP is seeking to understand confront all regions: they hold a particular challenge for developing regions where growing populations may intersect increasing rates of environmental change. In many tropical regions there are today both the cause of environmental change (e.g. biomass burning) and the effects (e.g. changes in atmospheric trace gases), and these cause-effect systems offer not only an environmental challenge but also a scientific opportunity to understand better the human effect on the biosphere. In addition, these regions hold important records of past environmental change that are important if we are to test models and ideas about future environmental change. Finally, in many developing regions there is not yet a sufficient scientific or policy community to participate fully in the global environment policy process (e.g. the Intergovernmental Panel on Climate Change). These considerations offer a challenge to IGBP, to the IGBP Core Projects, to the IGBP GAIM Task Force, and to the IGBP-DIS effort.

The African-GAIM Modelling Workshop will concentrate upon:

The Workshop will use models applicable to Africa in the global context, including terrestrial ecosystem and hydrologic models. Consideration will also be given to the IPCC global carbon inventory procedure. The models will be presented, run by participants in hands-on "laboratory"sessions, and interpreted in terms of African and global applications. Participants will conduct modelling projects during the workshop, to be subsequently developed at their home institutions as part of planned follow-up activities. These projects will be centered on a common theme of the effects of land use changes on African ecosystems and will be tailored to the needs of the participants and the ongoing IGBP research efforts in Africa. During the course of the workshop, the participants will each make short presentations of their own recent environmental/global change research.

The workshop participants will represent a teaching force which will maximize the positive impact of the workshop on building modelling capacity among the African global change research community. At the same time, the participants will bring to the workshop the necessary regional expertise to most effectively parameterize the models for application to Africa as well as for better constraining the contribution of African ecosystems to the global carbon and water balance. The modelling projects which emerge from the workshop will be applied directly to ongoing IGBP African research efforts.

Finally, in light of African population growth rates, the large extent of semi-arid ecosystems, and the dynamic interplay of land-use change and food production, Africa potentially will be severely tested by global environmental change. Consequently, it is important now to begin to develop in Africa the capability to consider the impacts and mitigation in the light of potential global change. These considerations need to be at continental, regional and local scales. Their context however must be considered within the global situation. The GAIM workshop hopes to contribute to this cause.

The African-GAIM Modelling Workshop will be one in a series of IGBP workshops in Africa in 1997. Others are indicated in the box below. The various workshops and their links with each other as well as with ongoing research efforts were discussed at a consultation between individual event conveners in Wageningen, The Netherlands (Oct. 15, 1996) where land use in Africa emerged as the common thread throughout the series of workshops. It is hoped that the coordinated series will produce a more useful result than a group of isolated workshops would have.

WORKSHOP WORKSHOP DATE, 1997
INQUA Paleomonsoon Workshop January 11-22
GAIM-African Modelling workshop March 3-12
GCTE Pest & Disease Vectors April-May
DIS Training Workshop for Francophone Countries May
WCRP/STAR/SCOWAR Climate & Food Security July
Hyrology in Sahel (BAHC-GCTE) September
LUCC in Northern Africa
October-November

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On the relation between biogeochemical systems, agriculture, climate and society

By Dork Sahagian

Numerous fora in the last several years have addressed Global Change and the role of an evolving society in the Earth system. Some have focused on present trends in identified biogeochemical cycles based on presently observed, reconstructed, and projected shifts in fluxes of critical components through various subsystems of the Earth system. Preliminary results of the analysis of observational data and simple models of some subsystems suggest that anthropogenic effects on the physical climate system may be significant and caused by the biogeochemical effects of atmospheric emissions from industry, agriculture, biomass burning, and land use change, among others. In the recent IPCC report ("Climate Change 1995, The Science of Climate Change") it was indicated that "the balance of evidence suggests a discernible human influence on global climate." One of the greatest challenges to current and future Global Change research programs is the accurate quantification of the interactions between chemical fluxes (CO2, CH4, N, P, etc.), energy utilization, land use changes for the purpose of agriculture, and societal food and resource needs.

Understanding of Global Change and future fluxes within the various components of the Earth system is primarily based on the development of reliable prognostic models of the physical climate, biogeochemical, and societal subsystems. These three subsystems are being addressed by international research programs WCRP, IGBP, and IHDP, respectively. While there have been some important advances in the understanding of the internal driving mechanisms in each of the three subsystems, the interactions and feedbacks between them is not well understood. Consequently, it is presently impossible to accurately predict the future boundary fluxes in any of the subsystems. Much improvement in modelling capabilities will be necessary before accurate projections can be made regarding the relationships between biogeochemical subsystems, climate, resource utilization, and human population growth and distribution. Advances will be necessary at the conceptual level in the form of better Earth subsystem models and model linkages, and at the information level with better and more comprehensive data regarding past and present land cover, biogeochemical fluxes and subsystem stocks and changes in soils, permafrost, ice, surface water and other supporting media. Also critical will be insights into the sensitivity of social systems to changes in biogeochemical systems, climate (e.g. precipitation patterns), agricultural productivity, and population growth. Clearly, each subsystem is sensitive to changes in the others. For example, climate is sensitive to biomass burning, deforestation, CO2 emissions from fossil fuels, and methane emissions from rice paddies. In turn, each of these is sensitive to societyÕs needs for food, resources, and energy. In this example, a critical link between the three subsystems is the emissions, agriculture, and food needs of a global society composed of a very disparate and rapidly changing distribution of industrial development and land use. As our understanding improves of the driving forces imposed on the Earth System by evolving human society and population dynamics, it will be possible to better integrate social research results of IHDP with biogeochemical results of IGBP and physical climate results of WCRP. Figure 1 is an adjusted "Bretherton Diagram" to better include Human Activities.

Figure 1:

Brethern Diagram

Figure 2 shows the details of the "Human Activities" part of the diagram, showing the mechanisms through which society influences global systems at three levels, from the most general outer "ring" to the most specific in the center.

The dynamics of population growth and redistribution are complex and only beginning to be understood. It is clear, however, that population growth is accelerating, and that the maximum growth rate is in the developing world. The U.N. "medium variant" population projections suggest that between 1990 and 2020 population will increase by 49% from 5.3 to 7.9 billion with large regional variations such as in Sub-Saharan Africa where a 124% increase is projected (T. Dyson, "Population and Food", Routledge: London, 1996). It is hoped that a better understanding of global biogeochemical systems and the links between these, the physical climate system, and agriculture will enable future societies to greatly increase food production, thereby increasing the standard of living in a world limited by food supply. However, a recent projection by the GCTE synthesis activity indicates that a necessary 2.3% per year increase in crop yields will be increasingly vulnerable to weeds, pests and diseases which can quickly track environmental changes. Human society is unique in the global ecosystem in that it possesses the ability to increase its food supply by altering land use from forest and shrubland, for instance, to cropland. Sustainable population growth is thus linked to available area and productivity of land being converted permanently to productive agriculture. This process bears directly on alterations in biogeochemical fluxes (e.g. CO2, methane, N, P) and thus on changing atmospheric composition and climate change. The position of human society in relation to "natural" systems can be integrated into the "Bretherton diagram" when interactions such as these are understood.

Atmospheric emissions have been identified and generally acknowledged as an undesirable mechanism of climate change. There have been calls for maintenance of CO2 emissions after 2000 at 1990 levels. This will keep the per capita emissions constant if population remains constant. While energy utilization efficiency may improve in developed countries, the possible reduction in emissions would not be sufficient to offset significant increases in the per capita emissions of the much more populous developing countries. A constant emissions scenario thus calls for curbing industrial and economic development of the developing world. It is thus not likely that this constant emissions scenario will be achieved, even if population were to remain constant at the 1990 level.

Consequently, in models which include land-use change, agriculture, and society, it is critical to include the relationship between population and agricultural productivity as well as industrial development. It is also critical to include the associated changes in land use and atmospheric emissions in biogeochemical models which in turn include important fluxes necessary for physical climate models and their feedbacks to terrestrial ecosystems and agriculture. When each of the subsystem models are internally complete and fully linked to each other, models of the Earth system will emerge with a level of reliability which will enable accurate prediction of Global Change in terms of temperature and precipitation patterns, storms, sea level, biome and agricultural shifts, glacial variations, and each of the many other components of the Earth system which act in concert to produce an environment for human society.

Schematic representation


Acknowledgments- Thanks go to Joao Morais of the IGBP Secretariat for stimulating discussions about social systems and global change, comments on the text, and for providing the figures. Top


GAIM Integration Program

By Berrien Moore III and Dork Sahagian

As GAIM develops and matures, we will embark down an additional path, armed with the model development and intercomparison experience obtained to date. This path leads toward global system integration, and was discussed in some detail at the first IGBP Congress in April of this year. As Earth subsystem models develop to a more robust level, GAIM is preparing to enter an integrative phase. This will involve the establishment of techniques for coupling and integration of biogeochemical subsystem models in preparation for the construction of an integrated prognostic biogeochemical model. Such integration will involve coordination with each of the IGBP Core Projects. The integration program will be structured in three segments, each contributing to the overall objective of developing the modelling capacity which will ensure the achievement of GAIMÕs goals. The first will be at the subsystem level, where GAIM activities will be designed to bring developing subsystem models into boundary compatibility. This will be done through modelling workshops involving intercomparisons of like subsystem models, and intercomparisons involving coupling between adjacent subsystem models (which must match boundary conditions and fluxes). The second segment will be at the system level, where simple Earth system models are compared to highlight differences in coupling techniques, inter-element fluxes, and sensitivity studies to reveal the differences between models of the relative importance of individual system parameters. The third segment will be at the IGBP Core Project level, where GAIM will work with Core Project modelling teams to help facilitate inter-subsystem coordination.

Subsystem models
The subsystem integration plan involves four key linkages: Land-atmosphere, ocean-atmosphere, atmospheric physics with atmospheric chemistry, and Land-ocean. These subsystems have different space and time scales (which themselves depend upon what is being tracked) and are often quite stiff as linked systems and therefore difficult in perturbation experiments. There are also greatly differing degrees of parameterization with little understanding as to effects.

Important linkage experiments, however, can NOW be done: a) the ocean carbon model inter-comparison project has linked atmosphere GCMÕs (mainly as drivers) with ocean GCMÕs containing carbon chemistry and crude biology; b) similarly, the terrestrial carbon models (NPP efforts) are being driven (partially) by GCM results; and c) we are taking the preliminary steps with the GCM Atmosphere transport codes studies for tackling the chemistry connection.

Subsystem models are being developed at present with a variety of structures and emphases. While each model is taken to represent the processes within a biogeochemical subsystem, the analytical and numerical formulations are widely disparate, and often lead to significant differences in model results. A fundamental issue is the development of subsystem models in such a way that the boundary conditions and fluxes for each will be compatible with each of the others. This compatibility is defined in terms of the ability of each model to provide the necessary input to define the boundary conditions needed to most efficiently run the others. For example, the boundary between the terrestrial and marine biogeochemical systems involves physical and chemical conditions and fluxes which are so complex that no single subsystem model presently accounts for all. Thus, matching boundary fluxes at the boundary would is impossible unless carefully coordinated during the model development phase.

As each of the subsystems becomes better understood and models converge on realistic values of output parameters, it will be timely to convene workshops to couple compatible models to form a more complete Earth system model. While it is not necessary to assume (and not possible to mandate) that all models of a particular subsystem will have identical input/output parameterizations, it is essential the each model be coupled only to other subsystem models with compatible parameterizations. Thus we envision the emergence of a suite of coupled models, each with consistent coupling and interactions between model components, but each based on a different style of formulation. The parallel development of coupled Earth system models has several advantages. The first is that because no single model (even an integrated Earth system model based on compatibly coupled subsystem models) accounts for all processes and interactions in the Earth system, each model will necessarily result in slight differences in inter-component fluxes and sensitivities. This will set the stage for Earth system model intercomparison which will highlight the relative importance of the various processes, interactions, and feedbacks between subsystems modelled by each of the integrated models. This should ultimately lead to modified integrated models which correctly account for the interactions to which the Earth system is most sensitive, while becoming unburdened from those to which it is demonstrably insensitive.

System level
It is the ultimate mission of the GAIM Task Force to promote the development of integrated models of the EarthÕs biogeochemical system for eventual linking to the physical climate system studied through WCRP as well as the social systems studied through IHDP. Simple models of the Earth system already exist, but they are not sufficiently robust to incorporate the detailed subsystem models being developed throughout the IGBP. It will nevertheless be instructive to examine such simple holistic models because some features which emerge may help identify and thus forestall potential problems in developing more comprehensive models on the basis of subsystem model coupling. Important insights can be gained from existing simple models of the Earth system, so we will build on these simple models in two ways:

1.)an organized simple but total Earth System Model approach that raises difficult system dynamics issues (chaos, feedbacks, parameterization sensitivities, etc.), and

2.)an effort to collect and document existing models of key features of the Earth System (e.g. Carbon Cycle) that could run on a 386/486 class machine (or run over the www). The purpose of the former is to highlight key scientific issues that may be lost in the large model efforts; whereas, the purpose of the latter is more out-reach and educational.

In order to assess the validity of Earth system models, it is critical to understand the sensitivity of the system to each of the input data. Heuristic and mathematical models are becoming developed to a point where it is appropriate to consider model sensitivity. Consequently, it will be necessary to conduct model sensitivity analyses of dynamic vegetation models, ocean carbon cycle models, GCMs, and hydrologic models as well as for simple Earth system models with respect to the various input climate and ecological data. We will initiate this effort with a workshop in 1998 with the goal of evaluating the sensitivity of various subsystem models as well as simple Earth system models to specific input data sets and boundary conditions and to facilitate coupling of subsystem models. This will set the stage for the Second GAIM Science Conference, to be held in 2000.

IGBP Core Project Integration
Each of the IGBP Core Projects is developing models of the appropriate biogeochemical subsystems. The challenge to GAIM will be to couple the various subsystem models and develop an integrated Earth system model. Model coupling will require advance planning so that it will be possible to most effectively match boundary conditions and fluxes. Thus, input and output data sets will need to be assessed and standardized, model temporal and spatial resolutions will have to be matched or scaled where necessary, and common numerical protocols will need to be defined so that the necessary parameters will flow through one subsystem model to the next. GAIM will work closely with the Core Project modelling activities to assist in developing models which will capable of effective coupling in the future.

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