8

Observations

INTRODUCTION

The U.S. Global Change Research Program (USGCRP) has responsibilities to observe, document, and understand global change and to predict it to the extent possible. The USGCRP does this by concentrating on five science areas: seasonal-to-interannual variability, decadal-to-centennial variability, atmospheric chemistry and ultraviolet-B radiation, ecosystems, and human dimensions—areas described in the previous chapters. By far the largest share of USGCRP funding goes to making observations to accomplish both the aims of the science areas and those of observing and documenting global change.

This chapter constitutes the link between the scientific foundation established in Chapter 2, Chapter 3, Chapter 4, Chapter 5, Chapter 6 through Chapter 7 and the course of action now required. The scientific foundation for each of the six primary science areas—biology and biogeochemistry of ecosystems, seasonal-to-interannual climate change, decadal-to-century climate change, atmospheric chemistry, paleoclimate, and the human dimension of global change—consists of a statement of the following: scientific character of the problem, selected case studies, key unanswered scientific questions, lessons learned in the course of scientific research over the past decades, and research imperatives.

The research imperatives are central. They connect theory and observation, defining the specific observations that are required. They connect priorities and resources and science with public policy. They separate, as direct experience has shown, success and failure. Together with consideration of the lessons learned, they establish the foundation for an effective scientific analysis of the Earth system.

Several basic scientific approaches, which set observational demands, can be distinguished: testing specific hypotheses—hypotheses that seek to define mecha-



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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade 8 Observations INTRODUCTION The U.S. Global Change Research Program (USGCRP) has responsibilities to observe, document, and understand global change and to predict it to the extent possible. The USGCRP does this by concentrating on five science areas: seasonal-to-interannual variability, decadal-to-centennial variability, atmospheric chemistry and ultraviolet-B radiation, ecosystems, and human dimensions—areas described in the previous chapters. By far the largest share of USGCRP funding goes to making observations to accomplish both the aims of the science areas and those of observing and documenting global change. This chapter constitutes the link between the scientific foundation established in Chapter 2, Chapter 3, Chapter 4, Chapter 5, Chapter 6 through Chapter 7 and the course of action now required. The scientific foundation for each of the six primary science areas—biology and biogeochemistry of ecosystems, seasonal-to-interannual climate change, decadal-to-century climate change, atmospheric chemistry, paleoclimate, and the human dimension of global change—consists of a statement of the following: scientific character of the problem, selected case studies, key unanswered scientific questions, lessons learned in the course of scientific research over the past decades, and research imperatives. The research imperatives are central. They connect theory and observation, defining the specific observations that are required. They connect priorities and resources and science with public policy. They separate, as direct experience has shown, success and failure. Together with consideration of the lessons learned, they establish the foundation for an effective scientific analysis of the Earth system. Several basic scientific approaches, which set observational demands, can be distinguished: testing specific hypotheses—hypotheses that seek to define mecha-

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade nisms, whether chemical, biological, or physical, that control the Earth system and its climate; defining the degree to which the Earth system has changed and is changing over periods of years, decades, centuries, and millennia; and (c) exploring largely uncharted regions, which may be defined geographically, mechanistically, or in other scientific terms. In the course of establishing an observational approach it is essential not to lose sight of this distinction. There are also important distinctions in the required datasets for the different disciplines. These distinctions are the basis of fundamental “cultural” differences in the architectures selected for specific observational approaches. For example, observations are obtained in different ways to address questions about different phenomena, such as the following: Ice cover changes as a function of time on seasonal-to-decadal scales. Free radicals at the parts-per-trillion level in the troposphere and the stratosphere. Vegetation pattern changes in terrestrial systems and oceanic systems. Secular trends in atmospheric temperature with an accuracy of 0.1 K, as a function of altitude, latitude, longitude, and season. Mesoscale meteorological events tied to global-scale variations such as the El Niño-Southern Oscillation (ENSO). Observations required for each of these phenomena are not obtainable through a single solution, such as a single global network of ground-based observations or an ensemble of space-based remote sensors. While considerable intrinsic programmatic pressure exists for a “unified ” solution to Earth observations, the scientific context speaks strongly for a flexible and adaptive aggregate of techniques that attack specifics, whether of long-term trends or of mechanisms that control the Earth system. A series of examples in Chapter 2, Chapter 3, Chapter 4, Chapter 5, Chapter 6 through Chapter 7 also represented a broad spectrum between observational constraint and theoretical speculation. The scientific method is pursued in an effective and vital manner when the fundamental design of the observational approach is matched to the calculated observables such that specific mechanisms, fundamental to the system, are tested directly. Models are very powerful when used in this context (see Chapter 10). They are central partners with observations in the course of proving or disproving fundamental assumptions. This report approaches the problem of observations as a synthesis, working from scientific research needs to observational implementation. It has always been assumed that building a global observing system would serve the needs of most of the science components of the USGCRP. Indeed, a parallel activity is taking place (Global Climate Observing System, GCOS) to design a global observing system for climate to satisfy both scientific and monitoring needs.1 Parallel efforts are under way for the ocean (Global Ocean Observing System) and

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade the land surface (Global Terrestrial Observing System); the climate modules of these systems are identical to the ocean and land modules of GCOS. However, it is our impression that there is no guarantee that such an observing system, even if it could be built at this time, would (or could) satisfy research needs. By designing a multiuse observing system for research purposes and then adapting it to meet global observing and monitoring system needs, there is some assurance that both research and monitoring needs will be met in an orderly manner. The model used here depends first on satisfying the needs of the science areas of the USGCRP, transitioning those parts of the system that can be made operational and then seeing how close to a global observing system we have come. OBSERVATIONS REQUIRED FOR THE SCIENCE ELEMENTS OF THE USGCRP As stated, the issue of observations is approached here in a synthetic manner. Scientific research needs were examined in Chapter 2, Chapter 3, Chapter 4, Chapter 5, Chapter 6 through Chapter 7. For each element described in those chapters the observational implications of those research needs are examined. These implications are examined in this section at the level of detail representing the state of the science in each of the subject areas. Given the disciplinary breadth of the USGCRP, the requirements are quite heterogeneous in both content and method of presentation. For example, observational requirements for the Global Ocean-Atmosphere-Land Surface (GOALS) program are detailed in another National Research Council report that is in press and are only summarized here. For other elements, such as the biology and biogeochemistry of ecosystems area, arguments leading to the observational requirements are repeated here for clarity. This chapter is also limited to discussion of observational needs and not the technology to supply those needs. Of particular interest is the degree of commonality among the observational requirements of the science elements, despite the disciplinary differences. For example, the need to observe radiatively active gases in the atmosphere is common to atmospheric chemistry, ecosystems, and decadal to centennial climate change research areas. Observations of streamflow, atmospheric and sea surface temperatures, and precipitation are emphasized across science elements. These common needs are not necessarily surprising, but they do emphasize the importance of such basic long-term measurements for the disciplines of global change. Biology and Biogeochemistry of Ecosystems The Research Imperatives for ecosystems research, as defined in Chapter 2, are: Land surface and climate. Understand the relationships between land surface processes and weather prediction and between changing land cover and climate change.

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade Biogeochemistry. Understand the changing global biogeochemical cycles of carbon and nitrogen. Multiple stresses. Understand the responses of ecosystems to multiple stresses. Biodiversity. Understand the relationship between changing biological diversity and ecosystem function. Research on global ecosystem processes motivates four broad classes of observations and experimental studies, shown below. As noted in Chapter 2, large-scale measurements in ecology tend to support all of the research imperatives above in a crosscutting fashion, with any one measurement set helping to test a variety of hypotheses. Ties of these measurement areas to the research imperatives are shown in Table 2.2. The four key measurement areas are time series observations of ecosystem state; land use and land cover change; site-based networks; and measurements of diversity, functional diversity, and ecosystem function. Time Series Observations of Ecosystem State Global time series of vegetation and phytoplankton state, derived from the National Oceanic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVHRR) and Coastal Zone Color Scanner sensors, for land and ocean, respectively, have proven their value in understanding the seasonal and spatial characteristics, interannual variability, and trends of large-scale biogeochemistry and biophysical processes.2 Space-based measurements of ecosystem state are fundamental in determining the link of terrestrial ecosystems to climate, the biogeochemistry of the land and oceans, and the impacts of climate and other disturbances. While measurements of “greenness” and ocean color are not direct ecological properties, they have proven to be highly correlated with spatiotemporal dynamics of ecosystems. Recent work3 highlights both the utility of these records and the dependence of the science on long and consistent records. Stable calibration and removal of the atmospheric signals of ozone, water vapor, and aerosols are critical to detecting ecological signals. While there is ample room for innovation in land surface remote sensing, stable calibration and correction impose stringent requirements on the sensor or sensors deployed. New instruments, while adding new capabilities, must also be “backwards compatible” to preserve time series. Atmospheric correction requires that coincident observations to quantify water, ozone, and aerosols be available for use in land surface retrieval algorithms. Spatial and temporal resolution for time series instruments are typically a compromise between sufficiently high spatial resolution to resolve ecosystem structure (0.25 to 1 km2) and swath width and data rate limitations associated with near-daily coverage. High temporal coverage is needed to ensure adequate sampling of seasonality, especially in cloudy environ-

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade ments. These requirements apply generally for both terrestrial and marine ecosystems; marine ecosystems add additional instrument requirements to avoid saturation by sun glint or high reflection. Data for land cover change require higher spatial but lower temporal resolution. Land Use and Land Cover Change Changing land use and land cover are fundamental drivers of global change and direct reflections of human activity and impacts. Land use changes have profound effects on the biogeochemistry of carbon, infrared active gases, photochemically active gases, and aerosol production (via dust and biomass burning). Land use changes also affect hydrology and erosion and, by changing surface albedo and energy exchange, can have direct effects on climate. People often create highly heterogeneous landscapes, mosaics that can encompass activities with highly divergent effects on ecological processes. The spatial arrangement of landscapes can affect exchanges of water and associated solutes and particulates in freshwater and coastal margin areas, with land cover at the land-water margins having substantial effects on water chemistry. The arrangement of landscapes also affects biological diversity, invasibility, and extinctions. Data on land cover and its change over time must thus capture the spatial scales of natural and human patterns. Space-borne sensors with resolutions from a few square meters to tens of square meters have proven to meet these needs.4 Sensors with two to seven spectral bands are adequate for land cover mapping, although new technology employing spectrometers,5 radar, or lidar has great potential. As in measuring ecosystem state, “backwards compatibility” must be preserved to continue existing time series when new technology and capability are introduced. Site-Based Networks In situ measurements of ecological processes tend to be highly multivariate. In terrestrial systems, understanding a measurement of CO2 flux and determining net primary productivity (NPP) require sampling multiple plant parts (leaves, wood, roots), often of several life forms (e.g., co-occurring grasses, shrubs, and trees). The plant parts are then analyzed for carbon and nitrogen. Understanding spatial variations in gradients of atmospheric CO2, 13CO2, CO18O, or O2 requires a network of measurement sites over large areas. To understand this process, leaf physiology, soil microbial processes, water fluxes, and other variables must be determined. Parallel issues arise in marine ecosystems regarding trophic dynamics and transport. At many sites, measurements are made as part of an experimental design including controls and various manipulations (e.g., of nutrients, species composition, disturbance frequency). These measurements are the essence of ecological data: the satellite and other geographic data serve to knit together disparate process studies in space and time. While there is much

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade interest in a common set of quantities in ecological site studies (quantities such as CO2, trace gas and water fluxes, NPP, nutrient availability, and species composition and diversity), achieving consensus on a core set of measurements, standard methods, and data formats is just beginning. No global-scale experimental design implementing such sites is in place to sample marine and terrestrial ecosystems, although such a design is proposed by the International Geosphere-Biosphere Programme (IGBP), using long baseline transects across ecological gradients. A high priority of global ecosystem science is to develop a network of appropriately sited atmospheric concentration and isotope, flux, and ecological process sites. Both the overall experimental design and the suite of measurements and methods must be decided. Minimally intrusive measurements (e.g., flux measurements) and manipulations (e.g., of CO2 concentration) must be components of such a network design. Recent advances in hyperspectral measurements made directly and remotely have established that remote sensing of foliar chemistry will be an important element in producing large-scale spatially explicit estimates of forest ecosystem function. During the past decade, a number of studies were conducted to determine if data from the National Aeronautic and Space Administration's 10-nm spectral resolution Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) could be used to make canopy nitrogen and lignin measurements. AVIRIS channels in the visible and infrared regions were correlated to field-measured foliar nitrogen and lignin.6 Estimates of canopy foliar nitrogen were used as input to the primary production model7 to determine ecosystem productivity at the Harvard Forest, in Massachusetts. At Blackhawk Island, AVIRIS-derived foliar lignin was used to determine nitrogen mineralization rates using a relationship observed by Wessman et al. (1998). These and other results suggest that direct measurement of forest canopy chemistry characteristics, based either on field measurements or via remote sensing, may provide simple, direct scalars of current forest productivity potential. In the coming decade, a space-based system will replace AVRIS, and the application of these techniques can be made at research sites globally. Measurements of Diversity, Functional Diversity, and Ecosystem Function The issue of diversity and species composition changes has emerged as a critical topic for global change in recent years. It is clear that the functional diversity of the Earth's biota is a first-order control over global ecosystem function, but how changes to the biota will affect global ecosystem function still is a young research topic. 8 Designing a global observing system and network of experimental studies, analogous to those described above for biogeochemical fluxes, is premature; the necessary monitoring and manipulations at global scales are currently far from obvious. But a major exploratory effort involving manipulations, studies of ecosystem function in the face of ongoing invasions, extinctions, species range shifts, and global monitoring of species diversity, invasion,

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade and extinction rates are all needed. These exploratory studies will lay the groundwork for a more systematic attack. The foundation for systematic study and monitoring of changing diversity and functional diversity must be laid quickly and a global research program put in place. Key Measurements for Ecosystem Studies Based on these considerations, the tables below present time- and space scales of critical in situ (Table 8.1) and remotely sensed (Table 8.2) measurements for terrestrial and marine ecosystem studies. These tables present examples of issues, measurements, and timescales, but they are not exhaustive. Seasonal to Interannual Climate Chapter 3 sets forth three broad Research Imperatives: ENSO prediction research, global monsoon research, and land surface exchanges, downscaling, and terrestrial hydrology research. These imperatives, as in other chapters, frame the observational requirements. ENSO Prediction Research Imperative The ENSO prediction process—predicting aspects of sea surface temperature (SST) and corollary variables—requires data to initialize the coupled models and data to evaluate the skill of the predictions. Because SST is the crucial variable to predict, weekly fields of SST at the 1° × 1° level are absolutely essential. These observations are currently provided by AVHRR, combined with in situ drifters to pin down the absolute values and gradients of SST. The key variables for initializing the model are the state of the atmosphere and the density state of the upper ocean. The state of the atmosphere does not seem to be as critical for initialization, since the model atmospheric state rapidly adjusts to the initial SST. In any case, the state of the atmosphere is provided by the twice-daily analyses from the operational weather prediction models. The internal state of the upper ocean can be assessed in two separate ways: directly by temperature-measuring instruments, on a line connecting a surface mooring to a bottom anchor, or indirectly by applying observed heat and momentum fluxes over the ocean component of the coupled model for a long period of time (usually exceeding 20 years). In practice, salinity is very difficult to measure and does not make a major contribution to the initial thermal state, so the direct method measures only temperature. The indirect method depends primarily on measuring the momentum fluxes with the heat fluxes parameterized, so that only the surface winds are used in the calculation. Currently, ocean models are initialized by combining the two methods above, assimilating both the long-term history of the wind fields and the currently ob-

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade TABLE 8.1 Time and Space of key IN Situ Measurements for terrestrial and Marine Ecosystem Studies Issue Measurement Measured or Inferred Quantities Temporal Resolution, Duration of Interest Sampling Strategy Technology Changes in climate forcing to ecosystems. Temperature, precipitation, radiation, wind speed, humidity. Surface climate. Daily to weekly, seasonal to interannual. Major biomes, elevation zones, climate regions, oceans. Automated or manned stations, data assimilation. Land surface effects on physical climate. Water, CO2, heat, momentum fluxes, net radiation. Evapotranspiration, sensible heat, albedo. Daily to weekly, seasonal to interannual. Major biomes with replication along climate gradients within biomes. Eddy covariance, micrometeorology. Land surface effects on global hydrological cycle and the climate system. Streamflow. Runoff, water balance, freshwater inputs to oceans. Daily to weekly, seasonal to interannual. Major biomes with replication along climate gradients within biomes. Gauged watersheds, major rivers. Spatial-temporal effects of climate and ocean circulation and mixing on carbon fixation. Water (on land), nutrients (land and sea), CO2, heat and momentum fluxes, net radiation. Net ecosystem exchange, carbon balance, CO2 flux-climate relationships. Daily to weekly, seasonal to interannual. Major biomes with replication along climate gradients within biomes; ocean regions. Eddy covariance, micrometeorology on land, short-term assays in marine and aquatic systems.

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade Spatialt-temporal changes to the nitrogen cycle. Nitrogen gas emissions and deposition. Nitrogen inputs and losses, emission of chemically active species. Daily to weekly, seasonal to interannual. Major biomes with replication along climate gradients within biomes; ocean regions. Eddy covariance, eddy accumulation, chamber measurements, concentration profiles. Spatial-temporal changes to nutrients in aquatic systems. Streamwater nutrient and organic matter concentrations and estuarine fluxes. Nitrogen losses from terrestrial systems, terrestrial inputs to the oceans. Daily to weekly, seasonal to interannual. Major watersheds. Gauged watersheds, concentration measurements of solutes. Changes in pollution inputs to ecosystems. Nitrogen, sulfur, ozone deposition. Nitrogen, sulfur, acidity, ozone stress. Daily to weekly, seasonal to interannual. Major biomes and airsheds, ocean regions. Eddy covariance, eddy accumulation. Increasing CO2 effects on ecosystem processes. CO2 enrichment experiments. Response of ecosystem function and carbon storage to increasing CO. Daily to weekly, seasonal to interannual. Major biomes with replication along climate gradients in biomes. Open-topped chambers, free air CO2 enrichment.

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade TABLE 8.2 Time- and Space Scales for Key Remotely Sensed Observations for Ecosystems Studies Research Area Measured or Inferred Quantities Temporal Resolution, Duration of Interest Spatial Resolution and Coverage Technology Vegetation feedbacks to climate, Leaf area, light intercepted by foliage and, by inference, evapotranspiration. Daily to weekly, seasonal to interannual. 0.25 to 1 km2, globally. Optical remote sensing, radiometry. Climate variability trends and vegetation response. Leaf area, light intercepted for photosynthesis and, by inference, primary productivity. Daily to weekly, interannual to decadal. 0.25 to 1 km2, globally. Optical remote sensing, radiometry. Land cover change. Ecosystem type (forests, grasslands, agriculture) over time and, by inference, rates of land use change needed for calculating changes to ecosystem-atmosphere fluxes (CO2, H2O, N2O). Seasonal, decadal. 1 to 100 m2, regional to global. Optical radiometry or spectroscopy, possibly radar or lidar in the future. Ocean color. Phytoplankton abundance and, by inference, marine primary productivity. Daily to weekly, seasonal to decadal. 1 km2, global oceans. Optical radiometer.

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade tained thermal state of the upper ocean, to arrive at an optimal estimate of the ocean's current thermal state. The subsurface ocean data are provided by a network of 70 moored TAO (tropical atmosphere-ocean) arrays in the tropical Pacific Ocean (providing approximately 2° of meridional resolution and 15° of longitudinal resolution) and by the ongoing XBT network. These same moorings measure winds, but, since the full TAO array has been in existence for only two years or so, historical winds must be obtained from the Comprehensive Ocean-Atmosphere Data Set, gathered from individual ship reports from volunteer observing ships. Because the ENSO observing system described in Chapter 3 measures the quantities needed to initialize the ocean component of the predictions, it is vital that this array be continued. The ENSO observing system was designed on the basis of the scales of variability of the winds. It may turn out that either fewer or more moorings are required to optimize prediction skill. Other quantities also prove useful for initialization: Sea surface height, as measured by satellite altimetry and tide gauge stations scattered around the islands and coasts of the tropical Pacific. Currents measured on the equator where geostrophy is more problematic. Cloud cover and solar irradiance reaching the surface. Precipitation in those areas in and surrounding the tropical Pacific (and remotely in the areas that ENSO affects) to evaluate the skill of precipitation predictions. Upper-level water vapor to evaluate the effect of seasonal to interannual variability, as opposed to greenhouse feedback, of this quantity. The overall recommendation, therefore, is to maintain global SST measurements and maintain the ENSO observing system, especially the TAO array. Global Monsoon Research Imperative The GOALS program has devoted much effort to defining the observational requirements for global seasonal to interannual predictions. These requirements are summarized in Table 8.3. Note that variables are listed in priority order. Not surprisingly, there is virtually complete overlap between these variables and those identified as important in pursuing the other seasonal to interannual research imperatives identified in the following section. Only the variable of land surface energy fluxes is not identified both below and in the following section. Land Surface Exchanges, Downscaling, and Terrestrial Hydrology Research Imperatives The primarily hydrological observational datasets needed to support research imperatives in the areas of land surface exchanges, downscaling, and terrestrial hydrology can be described as follows.

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade such as clear, scattered, broken, and overcast—these categories were much broader than those typically reported by human observers. Moreover, the combination of automated lidar reports and geostationary satellite estimates indicated fewer overcast and more clear conditions compared with human observers. This result may have been overcome with appropriate transfer functions, but the cloud algorithm from the geostationary methods depended on an NWS “first guess” field of their operational model. A major change in this model produced still another bias in the record. At this time, there is no suitable replacement for human observations of cloud amount at the several hundred sites across North America that had been reporting cloud amount and height for many decades. In response, the NWS has made an effort to continue both manual and automated cloud measurements at a selected number of stations for an indefinite period. Unfortunately, these cloud reports appear in a supplementary coded field message and are often missing. Conclusions from Case Studies As the above case studies demonstrate, there are a number of instances in which observing systems have faltered in delivering a consistent and calibrated record of global change. There are also some indications that many of the same problems may continue to appear in both ground-based and satellite observations relied on by virtually all of the science elements. For example, support for NOAA's Cooperative Observing Network, which is the basis for many of the longest surface temperature and precipitation records, continues to be a matter of concern. It also appears increasingly likely, based on current plans, that there will be a substantial gap between the end of the EOS PM-1 mission and the launch of the NPOESS. Such a gap would lead to data omissions and offsets in many of the data streams important for global change. TOWARD A PERMANENT OBSERVING SYSTEM Clearly, the USGCRP has the responsibility to observe, document, understand, and predict, to the extent possible, future changes in the global environment. The demonstration of, for example, secular trends in the Earth's climate requires analysis at the forefront of science and statistical analysis. Model predictions have been available for decades, but a clear demonstration of the validity of such predictions—a demonstration that would convince a reasonable critic on cross-examination—is not yet available. This lack is not in itself either a statement of failure or a significant surprise. It is, however, a measure of the intellectual depth of the problem and the need for carefully orchestrated long-term observations. The requirements for accuracy, continuity, calibration, in-flight standards, documentation, and technological innovation of long-term trend analysis are elsewhere described31 and are endorsed by this report. See Box 8.3 for a summary of

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade BOX 8.3 Many of the observational issues raised in this chapter follow recommendations made over a number of years by other NRC reports. Below are some examples: TOGA: A Review of Progress and Future Opportunities, National Academy Press, 1990, 66 pp. “It is ironic and unfortunate that the new TOGA initiatives for long-term observations of the global atmosphere are being implemented in the face of an overall deterioration in some of the key elements of the World Weather Watch, whose long-term stability was taken for granted in the TOGA strategy document. . . . Some of the weather services are being forced to cut back on their contributions to the conventional observing system.” (p. 55) Opportunities in the Hydrological Sciences, National Academy Press, 1991, 348 pp. “Improvements in the use of operational data require that special attention be given to the maintenance of continuous long-term data sets of established quality and reliability. Experience has shown that exciting scientific and social issues often lead to an erosion in the data collection programs that provide a basis for much of our understanding of hydrological systems and the document changes in regional and global environments.” (p. 11) A Decade of International Climate Research: The First Ten Years of the World Climate Research Program, National Academy Press, 1992, 55 pp. “The WCRP has not been successful in convincing [others]. . . to halt the decay of conventional observing systems in the tropics.” (p. 49) “Despite their importance, present capabilities for monitoring the climate system are deteriorating. . . Substantial effort by the WCRP. . . is required to. . . ensure baseline institutional and governmental commitment to the system.” (p. 54) Ocean-Atmosphere Observations Supporting Short-Term Climate Predictions. National Academy Press, 1994, 51 pp. “When a set of observations begun under research funding is suggested for ‘transition' to an operational agency, both the research and operational sponsors must be clear that the receiving agency has a commitment to sustain the observations, the technical capability to do so successfully, and avenues for the ongoing involvement of scientists.” (p. 2)

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade “Most satellite estimates will always require coincident direct-surface and upper-air measurements to perform the ongoing task of calibration, and surface platforms will be needed to make measurements not possible by remote sensing. The best determinations of the geophysical fields of interest will be obtained by combining satellite sensors with the direct observations of greater accuracy or more direct connections to the geophysical parameters of concern. Therefore, a well-chosen network of direct observations will become more, not less, important as satellite techniques advance.” (p. 3) Preserving Scientific Data on Our Physical Universe: A New Strategy for Archiving the Nation's Scientific Information Resources, National Academy Press, 1995, 67 pp. “Observed data provide a baseline for determining rates of change and for computing the frequency of occurrence of unusual events. They specify the observed envelope of variability. The longer the record, the greater our confidence in the conclusions we draw from it.” (p. 1) Learning to Predict Climate Variations Associated with El Niño and the Southern Oscillation, National Academy Press, 1996, 171 pp. “For future progress in the study of climate variations, it is essential to maintain what we already have, including the upper-air observing network, satellite altimetry, and the upper-ocean and surface-meteorological measurements made routinely in and over the ocean.” (p. 137) observational issues raised over a number of years in other NRC reports. While a complete discussion of observing selected variables is given in a collection of papers,32 we extract 10 principles that have emerged to provide the guiding considerations that underlie the USGCRP's responsibility for observing, documenting, and understanding global climate change. Principles of Long-Term Climate Monitoring The effects on the climate record of changes in instruments, observing practices, observation locations, sampling rates, and so forth must be known prior to implementing the changes. This information can be ascertained through a period of overlapping measurements between old and new observing systems or sometimes by comparing the old and new observing systems with a reference standard. Site stability for in situ measurements, in terms of both physical location and changes in the nearby environment, should also be a key criterion in site selection. Thus, many synoptic network stations, primarily used in weather forecasting

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade but that provide valuable climate data, together with all dedicated climatological stations intended to be operational for extended periods, must be subject to such a policy. The processing algorithms and changes in these algorithms must be well documented. Documentation of these changes should be carried along with the data throughout the data-archiving process. Knowledge of instrument, station, and/or platform history is essential for data interpretation and use. Changes in instrument sampling time, local environmental conditions for in situ measurements, and any other factors pertinent to the interpretation of observations and measurements should be recorded as a mandatory part of the observing routine and archived with the original data. In situ and other observations with a long uninterrupted record should be maintained. Every effort should be applied to protect the datasets that have provided long-term homogeneous observations. “Long term” with regard to space-based measurements is measured in decades, but for more conventional measurements long term may be a century or more. Each element of the observation system should develop a list of prioritized sites or observations based on their contribution to long-term monitoring. Calibration, validation, and maintenance facilities are a critical requirement for long-term climatic datasets. Climate record homogeneity must be routinely assessed, and corrective action must become part of the archived record. Wherever feasible, some level of “low technology” backup to “high-technology” observing systems should be developed to safeguard against unexpected operational failures. Data-poor regions, those variables and regions that are sensitive to change, and key measurements with inadequate spatial and temporal resolution should be given the highest priority in the design and implementation of new climate observing systems. Network designers and instrument engineers must be provided with long-term climate requirements at the outset of network design. This step is particularly important because most observing systems have been designed for purposes other than long-term climate monitoring. Instruments must have adequate accuracy, with biases small enough to document climate variations and changes. Much of the development of new observational capabilities, as well as much of the evidence supporting the value of those observations, stems from research-oriented needs or programs. The lack of stable long-term commitment to these observations and the lack of a clear transition plan from research to operations are two frequent limitations in the development of adequate long-term monitoring capabilities. The difficulties of

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade securing a long-term commitment must be overcome if the climate observing system is to be improved in a timely manner with minimum interruption. Data management systems that facilitate access, use, and interpretation are essential. Mechanisms that facilitate user access (directories, catalogs, browse capabilities, availability of metadata on station histories, algorithm accessibility and documentation, etc.) and quality control should guide data management. International cooperation is critical for successful management of data used to monitor long-term climate change and variability. The remainder of this section concentrates on the transition from a research-focused observing system to a permanent operational component within the observing system of the USGCRP for global environmental monitoring. This transition is an essential objective for the next decade of the USGCRP.a Some of the considerations below are relevant to all observing systems, whether space based or in situ, and are independent of platform. However, there is a particular challenge—the transition from the NASA polar platform series to the NOAA NPOESS series—that raises certain unique challenges that must be recognized. The Essential Transition: From Research to Long-Term Monitoring A monitoring system is needed to detect secular change in the global environment. Even for research purposes alone, the system must be in place long enough to see a few cycles of the changes. For the dec-cen and biogeochemical components of the USGCRP, this implies an observational system with a very long lifetime. Moreover, from an operational point of view of tracking changes in the environmental state of our planet, a system is needed essentially for the duration of the perturbations and responses. Obviously, such a multipurpose monitoring system would fulfill important research needs; however, its cost is likely to be significant, particularly when integral costs are considered and not just annual costs. Therefore, it must satisfy operational purposes if it is to be sustained. An essential shift is needed within the federal government: the federal government must recognize that monitoring the changes in the global environment on significantly longer timescales than demanded by operational meteorology is in the forefront of the national interest. For an observing system to be permanent, then, it must have some operational requirement. While in theory it is conceivable that some agency will adopt the rigors of accepting climate monitoring as an operational requirement, in a The ENSO observing system, an oceanographic array for initializing predictions of aspects of ENSO, is undergoing this transition from research to operations now. The process is described in detail in NRC (1994b).

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade practice the monitoring of climate variability is not currently an operational requirement of the USGCRP nor is there an agency of the U.S. government that accepts climate monitoring as an operational requirement and is committed to it as a goal. The current designs for a global observing system by the GCOS and the Global Ocean Observing System33 seem unattainable in practice because of the lack of such an operational mandate for any existing agency or the USGCRP. The prospects for a permanent observing system therefore seem to rest on three possibilities: The USGCRP accepts environmental global change-focused monitoring as an operational necessity and makes the institutional changes needed to enforce the discipline that operational requirements demand. A new coordinating mechanism is created that has operational climate monitoring as a founding requirement. The permanent observing system is built using a quite different paradigm —that of coherence and evolution. This paradigm sees individual components of the observing system growing out of research but being shifted into operations, each for its own purpose. As the system evolves, different parts of it may be operationalized for entirely different reasons. Thus, some parts of the ocean may be monitored for seasonal to interannual prediction, some for fish management, some for fish detection, some for pollution detection, and so on. The evolution process may take many years and only at some time in the future will it be appropriate to see what capabilities it has and what incremental measurements are needed to go from a congeries of individual measurements to an ocean observing system. One of the difficulties in implementing the new paradigm is the necessity of converting research funding to operational funding. A research program can maintain a permanent observing system only when the system is relatively cheap and does not inhibit other research objectives. When there is an operational need for a system, funding must not come from research sources, else the building of a permanent observing system could gradually impoverish the research enterprise. The paradigm still requires an institutional commitment to coordinate the various elements into the ultimate observing system, but it postpones the need for coordinated funding and thus allows (but does not guarantee) the coordination to evolve over the many years that would undoubtedly be required for this to occur. If we evolve the needed observational system as recommended, a system design study still will be needed.b There is a danger that without careful planning the system might contain a collection of instruments that do not together yield an adequate observing system to the scientific challenges, particularly those on the b See again the section on a multipurpose, multiuse observing system.

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade longer-term issues like ecosystems and climate from decades to centuries. A system design will give at least one measure of what is needed and, importantly, what is not. A key issue that initializes both the system design and beginning the evolution process is the current and forthcoming satellite research missions: the EOS AM-1 and EOS PM-1 NASA polar platforms, the Advanced Earth Observing Satellite platforms from Japan, and the current ERS-1, ERS-2, and the future ENVISAT polar platforms from Europe as well as several more specialized research missions (e.g., TOPEX-Poseidon [Ocean Topography Experiment], TRMM, and the future Earth System Science Pathfinders). Another force on the process is the convergence discussions in which NOAA and the U.S. Department of Defense (DoD) (the Air Force) are converging the current Television and Infrared Observation Satellite (TIROS) and Defense Meteorological Satellite Program (DMSP) systems, respectively, in which they will go from a four platform system in sun-synchronous orbits (equatorial crossings at early morning, midmorning, and two in the afternoon) to a two-platform system (an early morning and an afternoon equatorial crossing). This is the planned NPOESS. Taking over the important midmorning slot will be the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) with its meteorological operational (METOP) polar platform. There are several difficulties in going from the research missions to the operational missions. The current phasing of the EOS AM-1 and EOS PM-1 and the NPOESS schedule produces a potentially significant observational gap. This gap is currently increasing because of the longevity and reliability of the current assets (e.g., the TIROS and DMSP systems on orbit and in construction). What is to be done to appropriately fill the gap is not clear. The linkage between EOS AM-1 and the METOP midmorning platform of EUMETSAT is even murkier than that between NASA and the U.S. operational satellite agencies (NOAA and DOD). It is crucial for global change research and monitoring that future operational satellites should, to the extent practical, have the qualities necessary for global change science identified in this report. To resolve these difficulties and move onto a course that is sustainable and meets the long-term observational challenge posed by global change will require political courage and strong and continued leadership by all parties. It will not be easy; it is, however, essential.

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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade NOTES 1. Karl et al. (1995a). 2. Sellers et al. (1997), Fung et al. (1987), Myneni et al. (1997), Potter et al. (1993), Randerson et al. (1997), Braswell et al. (1997). 3. Braswell et al. (1997), Myneni et al. (1997). 4. Skole and Tucker (1993). 5. Wessman et al. (1998). 6. Martin and Aber (1997). 7. Aber and Federer (1991). 8. Vitousek et al. (1997), Braswell et al. (1997). 9. Wahl et al. (1995). 10. Kanciruk (1997). 11. Vörösmarty et al. (1996). 12. Rasmussen and Carpenter (1982). 13. E.g., Holton et al. (1995). 14. See Intergovernmental Panel on Climate Change (1995). 15. See Logan (1994). 16. See Wennberg et al. (1998). 17. National Research Council (1996). 18. Ibid. 19. Ibid., Russell et al. (1994). 20. National Research Council (1998b). 21. Wood and Skole (1998). 22. Entwistle et al. (1998). 23. Marland and Boden (1997). 24. Cleland and Scott (1987). 25. National Research Council (1997). 26. National Research Council (1994a). 27. Ibid. 28. Karl and Steurer (1990). 29. Ibid. 30. Quinlan (1985). 31. Karl et al. (1995a). 32. Karl et al. (1995b). 33. Ibid. REFERENCES AND BIBLIOGRAPHY Aber, J.D., and C.A. Federer. 1991. A generalized, lumped-parameter model of photosynthesis, evapotranspiration and net primary production in temperate and boreal forest ecosystems . Oecologia 92:463-474. Braswell, B.H., D.S. Schimel, E. Linder, and B. Moore III. 1997. The response of global terrestrial ecosystems to interannual temperature variability. Science 278:870-872. Cleland, J., and C. Scott. 1987. The World Fertility Survey: An Assessment.Oxford University Press, Oxford, U.K. Entwistle, B., S.J. Walsh, R.R. Rindfuss, and A. Chamratrithirong. 1998. Land-use/land-cover and population dynamics, Nang Rong, Thailand. In People and Pixels: Linking Remote Sensing and Social Science, D. Liverman et al., eds. National Academy Press, Washington, D.C.

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