Life Sciences: Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988)

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GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 59 3 Global Biology / Biospheric Science BACKGROUND Over the last two decades we have become aware that the traditional division of the sciences related to the study of the Earth—biology, oceanography, geology, meteorology—represents only an historic artifact inherited from eighteenth-and nineteenth-century scientific thinking. We are learning that the processes that characterize the Earth's environment transcend these boundaries, and that the traditional ''spheres''—biosphere, atmosphere, hydrosphere, geosphere—are parts of one complex system. As a consequence, we are witnessing the development of a new science, the science of Earth as a system—a discipline that as yet has no proper name. It is this new, unified science that the task group will address in this chapter with the (inadequate) terms "global biology" and "biogeochemistry." The perspective from space, which made it possible for the first time to capture in one glance the entire planet—with its continents, oceans, atmosphere, and biosphere, has contributed significantly to this growing conceptual synthesis. Because of this inherently global perspective, the task group feels that space science should develop and maintain a leading role in global biogeochemistry. The current divisions along the lines of traditional 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 60 sciences reflect themselves in the fact that, during this study, global biogeochemistry was addressed both by the Task Group on Earth Sciences and the Task Group on Life Sciences. To resolve this problem to some extent, the two groups have coordinated their approach. The Task Group on Life Sciences strongly endorses the concept of the "Mission to Planet Earth" discussed in a companion volume by the Task Group on Earth Sciences. In the current report, the Task Group on Life Sciences will limit itself to the discussion of the fundamental concepts that it feels will make up the basis for the space science effort in global biology and biogeochemistry in the period 1995 to 2015. For details of research planning and implementation it will refer in most cases to the Task Group on Earth Sciences report. Much of the conceptual background that forms the basis of the discussion in this report has been covered in two recent NRC reports: A Strategy for Earth Science from Space in the 1980s and 1990s (National Academy Press, 1985) and Remote Sensing of the Biosphere (National Academy Press, 1986). The document describing the Earth Observing System (EOS) (NASA T.M. 86129, August 1984) also provides much of the scientific background for the topics discussed here, as well as a description of the types of sensors the task group expects to be in orbit by 1995. The task group has considered the existence of an EOS-type system as the starting point for its projections. Before addressing the directions for space science in some specific areas— biosphere-atmosphere interactions, biogeochemical cycles, global ecology, evolution of the biosphere—some points that are fundamental for space science planning beyond 1995 must be discussed: sensor traceability, information nesting, and data handling. The detection of long-term trends (time scales of decades to centuries) is essential for our understanding of the response of the earth system both to the large-scale perturbations brought about by human activities and to the effects of geophysical changes. To detect such trends, the calibration of instruments and sensors has to be maintained over long time periods. When sensors are being replaced by new ones, the characteristics of old and new sensors need to be compared carefully. For example, the importance of long-term calibration traceability has become evident in the history of atmospheric carbon dioxide measurements, where the careful maintenance of calibration procedures has allowed the 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 61 unequivocal detection of historical trends. As a contrasting example, the lack of such traceability still obscures the existence of clear trends in acid deposition. The concept of information nesting requires that information obtained using space-based sensors be embedded in ground-and aircraft-derived data so that a continuity of the scales of observation can be obtained. Space observations have to be linked to ecologically and geochemically relevant variables through careful calibration with ground-based observations—so-called ground truth. This program must be integrated from the start in space research activities; it should not be assumed that the necessary ground-arid aircraft-based activities will be funded and undertaken by agencies other than NASA unless this has been coordinated in advance. Finally, the volume and character of the data stream that is expected to result from the deployment of a variety of sophisticated space platforms and sensors, and from the associated ground and aircraft activities, will require the development of new data handling capabilities. This development should precede the deployment of the data sources, such as satellites. Too many data exist already that are practically inaccessible due to neglect of data handling needs. The development of complex analytical and numerical models will be necessary; these models will have to be equipped to receive and process the multitude of ecological, meteorological, chemical, and geological data that will be available from the instruments suggested in this and the Task Group on Earth Sciences report. The requirements for data handling or modeling are described in more detail in a subsequent section. BIOSPHERE-ATMOSPHERE INTERACTIONS The biosphere and the atmosphere are intimately connected: the composition of the atmosphere is largely a result of the activities of the biosphere; on the other hand, the chemical and climatic characteristics of the atmosphere are essential for the support of life on Earth. Due to its relatively small mass compared to that of other components of the earth system, the atmosphere responds rapidly to changes in the input and output of both material and energy. This makes it valuable as a "fast-response sensor," but also makes it very susceptible to environmental impact from human activities. In the following sections, the task group will discuss the 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 62 needs for space research related to the interactions between the biosphere and global climate and atmospheric chemistry. Biosphere-Climate Interactions In this century, mankind began to conduct two very large, albeit inadvertent, experiments on the interactions between the biosphere and climate: the addition of carbon dioxide, and some other "greenhouse" gases to the atmosphere, which is expected to raise global temperatures, and the large-scale deforestation of the tropical rain forest regions. These "experiments" will reach such an advanced stage in the timeframe considered in this report that we can expect a clear climatic and biospheric response. Most of the trace gases that contribute to the greenhouse effect (carbon dioxide, methane, nitrous oxide, etc.) have biospheric sources and sinks as well as anthropogenic ones. It is essential that we understand the processes leading to their emission and removal, as well as their fluxes to and from key environments. This will require a combination of ground-based aircraft and space platform studies, which can be developed on the basis of the experience gained in experiments like the NASA GTE/ABLE and EOS projects. In conjunction with the activities in atmospheric chemistry discussed below, this research should lead to a model of atmospheric trace gas chemistry that would have predictive capabilities and that could be linked to climatic models in order to investigate the climate response to the expected combination of greenhouse gases. Currently, carbon dioxide is considered almost exclusively by atmospheric modelers, although the effect of other gases could be as important. Atmospheric aerosols have climatic effects that depend for their direction and magnitude on the chemical and physical characteristics of the aerosol. We need an improved understanding of the role of the biosphere in the production of aerosols and aerosol precursor gases, such as reduced sulfur gases. It is likely that biogenic aerosols have a significant influence on the albedo of oceanic clouds; we need to study this relationship using aircraft and satellite techniques. The effect of marine cloud albedo on the Earth's radiation balance is significant and requires further study. The large-scale change in surface characteristics due to tropical deforestation, desertification, and changing agricultural practices must be expected to influence substantially the transfer of 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 63 both heat and water vapor at the Earth's surface. The mechanisms and rates of energy and water exchange as a function of ecological and soil characteristics must be further investigated using a combination of active and passive remote sensing (microwave, infrared, visible) with ecological ground studies. A very important role could be played here by sensors that are deployed at ground level and which transmit their information to satellites, which in turn relay this information to data analysis centers. Remote sensing must be employed to keep track of the changes in extent and distribution of biogeographic zones. All these data will have to be integrated into climatic models to predict the response of the atmosphere. Conversely, as the effects of climatic change become apparent in meteorological observations, we will have to look for responses of the biosphere to these changes. These responses may not be readily detectable at ground level due to the large local variability of ecological parameters, but may be evident from the much larger data set accessible through remote sensing. A prerequisite for such studies will be a much enhanced ability to determine ecological variables by remote sensing and to process such data to a large extent by automated techniques. The Task Group on Earth Sciences report contains a detailed discussion on the relationship between the global hydrological budget and the biosphere. Largely as a result of satellite data, our understanding of ocean-climate interactions is steadily improving. The sensitivity of high-latitude climate to perturbations by the "greenhouse" effect and the importance of high-latitude regions in oceanic productivity make space-based studies of the interactions between oceanic productivity and climatic change—especially at high latitudes— an essential topic for future investigation. Most of the transport of surface water to the deep ocean—and consequently the removal of carbon dioxide to the deep waters—also occurs at high latitudes. Due to the difficulty of observation from ships, with regard to both spatial and temporal coverage, space studies will play an essential role here. We will require space sensors to determine pigment concentrations and to deduce oceanic primary productivity and (as far as possible) phytoplankton types. We will have to look for changes in marine biogeography and ecology in response to climatic change. From these studies we hope to gain not only fundamental information on global marine ecology, but also essential input to the management of marine resources. 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 64 Biosphere-Atmospheric Chemistry Interactions The role of the biosphere as a source and sink for most atmospheric constituents has already been mentioned. Biospheric processes are essential for the atmospheric content of carbon compounds (CH4, CO2, CO, alkanes, etc.), nitrogen species (NH3, NOx, etc.), sulfur compounds (H2S, (CH3)2S, H2SO4, COS, etc.), organohalogen compounds (e.g., CH3Cl), and many other molecules. For a number of these compounds, spaceborne sensors exist or are under development, for example, in the UARS (Upper Atmospheric Research Satellite) project. However, the use of these sensors is largely limited to the upper atmosphere. It will be essential to develop techniques for remote sensing of tropospheric constituents. These instruments will include active sensors, and will be operated from satellites and, to a large extent, from research aircraft. Again, integration of ground-based activities to determine biospheric exchange will be of vital importance. From the ground-based work we will obtain the relationships between ecological and meteorological variables and the biosphere-atmosphere exchange fluxes of trace compounds. This knowledge may enable us to predict these fluxes on the basis of variables accessible by remote sensing. This will be a prerequisite for making estimates of global fluxes between biosphere and atmosphere. A key role will be played here by the development of automated instrument systems that incorporate technology derived from planetary missions. These systems will include automated gas chromatographs to measure concentrations and fluxes of important biogenic gases (e.g., NO, CH4, and various sulfur gases), as well as sensors that determine quantitative chemical and biological information, such as soil microbial biomass, community structure, nutritional status, and metabolic activities. Other sensors will determine soil and sediment temperatures, pH, oxygen tension, soil moisture, and other parameters likely to affect microbial activity. The information collected by these automated systems will be relayed by satellite to data gathering and analysis centers. The incorporation of the biogeochemical processes deduced from in situ and remote-sensing measurements into appropriate models will enable us to forecast changes in atmospheric composition in response to biogeographic and climatic change. Chemical cycling of elements within the atmosphere involves 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 65 photochemical reactions, processes involving exchange with aerosols and cloud droplets, reactions in these condensed phases, and a variety of scavenging or deposition processes. Again, the development of remote sensing techniques to measure the concentrations of key species in the troposphere, and their deployment on a variety of platforms are essential for testing our concepts of atmospheric cycling. Differential adsorption lidar (DIAL) is one such technique. Biomass burning, especially in the tropical regions, has a very important influence on the chemical and physical characteristics of the atmosphere in the affected regions. Current efforts are under way to determine the characteristics of the emitted material and the relationship between the amount of biomass burnt and the amount of material emitted to the atmosphere. To estimate the regional and global emission rates as well as the biogeographical impact of burning agriculture, we will need remote sensing techniques to determine the size of the burnt areas and the amount of biomass that has been combusted. This could probably be done by existing or planned sensors, and is largely a problem of data processing and algorithm development. The application of space science to the study of stratospheric chemistry, especially with regard to the stability of the ozone layer, which is essential for the protection of the biosphere from solar ultraviolet radiation, is treated in detail in the report of the Task Group on Earth Sciences. GLOBAL ECOLOGY In considerations of global biology, much discussion has centered (appropriately) on the biota as a system or series of interlinked systems whose collective metabolic activities influence the atmosphere, hydrosphere, and climate. The task group endorses the recommendations articulated in the Space Science Board Committee on Planetary Biology's (1986) report Remote Sensing of the Biosphere and the report of the Task Group on Earth Sciences calling for measurements of biome distribution and productivity, with special consideration of such critical problems as tropical deforestation, desertification, and the systems ecology of actual or potential agricultural regions. As has been pointed out in detail above, accurate data collection will necessarily involve coordinated 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 66 measurements from observation platforms in space, high-and low-altitude aircraft, and from the ground. Advanced instrumentation systems will allow the integration of ground observations over appropriate areas and the gathering by satellites of data telemetered from remotely controlled, automated instrument packages. This will permit critical ecological data to be gathered from relatively inaccessible areas and make possible data acquisition on temporal and spatial scales that are unthinkable without space technology. The task group further stresses that the recommended global biology research initiative presents significant opportunities for research in organismic ecology. Several types of information central to ecological thinking are poorly known from traditional ecological observation. One important question concerns the equilibrium of ecosystems. Are ecosystems in a steady state with regard to nutrient and energy flux, biomass, or taxonomic composition? If so, on what temporal and spatial scales does a dynamic equilibrium obtain? What are the effects of perturbations of varying frequency and intensity (such as storms, drought, flooding, fire, disease), and how does the ecosystem respond to such perturbations? Does it return to some approximation of the predisturbance state, and if so, on what time scale does recovery occur? What conditions of perturbation will "permanently" alter the ecosystem? Models of community ecology (and related aspects of evolutionary biology) require information on the distribution of species populations within communities, as well as the spatial and seasonal distribution of phenological characters (flowering, fruit maturation, leaf fall, etc.). Such information can be difficult to obtain, particularly for tropical forests, where much of the Earth's diversity resides. Present satellite and aircraft remote sensors do not offer sufficiently fine-scale or discriminating data to resolve patterns of, for example, tree species distribution within a tropical forest. The task group recommends that technology be developed so that during the period 1995 to 2015 such resolution will become possible from aircraft. On a larger spatial scale, the task group recommends that technology be developed that will allow recognition of different successional stages within tropical forests. Such information, which is not available at present, is of theoretical importance and would be tremendously valuable to foresters charged with the management of forest resources. Organismic ecological issues are of significant theoretical and practical value in themselves, but they are also relevant to the 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 67 systems ecological measurements stressed in other reports. One simple question illustrates the point. Does the species composition of a community significantly influence its biomass and productivity, or will communities that have developed in physically comparable environments have comparable biomass and productivity regardless of taxonomic composition? The answer to this question will certainly influence our ability to integrate data and develop models for the evolution of the biosphere in geological time. Much of the organismic ecological research community is only dimly aware of the potential that NASA's global biology program holds for ecological research. If that potential is to be realized during the time period in question, some program of mutual education should be established between NASA and this community prior to 1995. The task group recommends that a series of workshops be initiated in cooperation with the Ecological Society of America. Global Ecology Models and Data Handling Since our goal is to understand the mutual interactions of the biota with the geosphere, the hydrosphere, and the atmosphere, we need to integrate vast amounts of complex observational and experimental data. We need to formulate new generalizations, new theories. To achieve this goal, we will have to model, in both the short term and the long term, the dynamics of the surface of the Earth, since these biogeochemical processes simultaneously affect and affected by the biota. The task group emphasizes that modeling is uniquely important to global biology due to the very large number of parameters and the quantity of data relative to other physical and biological sciences. Observational satellites, such as Landsat, or ground-based devices, such as those recording gas evolution, can measure numerous variables many times per day or even per minute. Experiments designed to measure seasonal fluctuations with high statistical validity may, in fact, contain evidence for circadian rhythms or other short-term phenomena. Such correlates would be lost by averaging in the course of data reduction, and would no longer be available when information is sought later that was not part of the original data reduction design. On the one hand, we cannot archive every bit of data for decades; on the other, we should not preclude serendipity by condensing data immediately to the logical needs of the proposed experiment. Each set of observations 

GLOBAL BIOLOGY / BIOSPHERIC SCIENCE 68 must be evaluated to strike a compromise. We need to develop an easy and rapid interactive system wherein the algorithms for data reduction can be altered as new phenomena are defined and the theories refined. We will have to begin by modeling various components of the earth system. The many component submodels resulting from this effort serve two functions essential to science: they provide a framework for summarizing and evaluating the data, and they provide tests of our generalizations. However, the development of a comprehensive model that relates the diverse investigations will be one of the fundamental goals of global biogeochemistry in the twenty- first century. In this endeavor, NASA must provide leadership. No other organization has the physical resources, the intellectual talent (in-house and by consultation), and the global perspective to weld together this new scientific discipline. Of course, much of this leadership will take the form of designing special instruments and making new measurements. But NASA's most important role in global biogeochemistry will be to unite heretofore disparate disciplines around a common theme.