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Introduction Rapidly evolving changes in the global environment have cap- tured the attention of scientists, policymakers, and citizens around the world: the increase of atmospheric greenhouse gases such as carbon dioxide, methane, and the chiorofluorocarbons; the expected consequent changes in global climate and sea level; global deple- tion of stratospheric ozone en cl the observed "antarctic ozone hole"; widespread desertification in many parts of the developing worI(l; massive tropical deforestation and reduction in the diversity of plant and animal species; extensive damage to mid-latitude forests; and acidification of lakes and soils in many regions. At the least, these changes have far-reaching and potentially disruptive implications for the worId's natural resources. In the worst case, the changes collec- tively threaten the life-support system of the earth. The problem of global environmental change is crucial and urgent. The scientific community is thus urgently challenged with pro- vicling to decision makers the best possible assessments of the future course of the global environment, assessments on which policies to mitigate and adapt to these changes can be based. Over the past decade, efforts to translate the agenda of environmental problems perceived by the public into a scientific agenda of clearly posed, tractable, and prioritized research problems have led to a unifying seminal insight: We cannot hope to understand fully or to predict meaningfully the course of any single Tong-term environmental change 5

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6 without understanding the earth system as an integrated whole, the changes in the system over the earth's history, and the ways in which anthropogenic activities interact with the system. Contemporary advances in technology, such as the ability to observe the earth from space and the rapidly accelerating capabili- ties for data handling, numerical modeling, and telecommunications, make such an ambitious venture possible at this time. Historically, revolutionary scientific advances follow the development of each new instrument that extends our vision of the real world. Invention of the telescope opened our understanding of the universe. The microscope led to revolutions in biology and medicine. Today, sateHite-borne sensors, worldwide communications systems, and supercomputers permit us to see our planet for the first time as an integrated whole. Disciplinary advances that have led to current understanding of the components of the earth system provide a launching point from which an integrated view of the system can processed. Thus, because of these advances in science and technology, understanding global en?'i- ronmental change is not only urgent; it is now possible. U.S. PROGRAM FOR THE STUDY OF GLOBAL CTIANGE Long-term changes in the earth have been addressed in a num- ber of national and international programs (e.g., the Global Atmo- spheric Research Program, its successor World Climate Research Program, and UNESCO's Man and the Biosphere Program) that provide a strong foundation for continued progress. Most recently, an extremely broad U.S. national effort in the study of global change has evolved based on the conceptual foundation of earth system science. This conceptual framework was developed in a multidisci- plinary study by the Earth Systems Science Committee of the Na- tional Aeronautics and Space Administration and has been used extensively by the National Science Foundation and the National Oceanic and Atmospheric Administration in planning their research programs on global change (ESSC, 1988~. The goal of earth system science is to obtain a scientific understanding of the entire earth sys- tem on a global scale by describing how its component parts and their interactions have evolved over the earth's history, how they function, and how they may be expected to continue to evolve. Because of the increasing evidence of potentially significant human influences on the earth system, the U.S. program focuses on the research necessary to

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7 predict those changes that wiB occur in the next decades to centuries, both naturally and through interactions with human activities. Currently, the U.S. program on global change centers on the study of the following seven elements identified by the Committee on Earth Sciences of the Federal Coordinating Council for Science, Engineering, and Technology (Committee on Earth Sciences, 1988~: ~ Biogeochemical dynamics to study the sources, sinks, fluxes, and interactions between mobile biogeochemical constituents within the earth system, with a particular focus on water, oxygen, carbon, nitrogen, sulfur, phosphorus, and the halogens. ~ Ecological systems and dynamics to study the responses of ecological systems, both marine and terrestrial, to changes in global environmental conditions and the influence of biological communities on the atmospheric, climatic, and oceanic systems. ~ Climatic and hydrologic systems to study the physical pro- cesses that govern the climate and hydrological system comprising the atmosphere, hydrosphere (oceans, surface ~.ncl ground water, and so on), cryosphere, land surface, and biosphere. Human interactions to study (1) the impact of human activi- ties on the global environment, including releases of nutrients, toxins, chemicals, and trace gases and changes in the use and cover of the land, such as desertification, and (2) the impact of changing global conditions on human activities. ~ Earth system history to uncover the natural record of environ- mental change contained in rocks, terrestrial and marine sediments, glaciers and ground ice, tree rings, geomorphic features, and other direct or proxy documentation of past environmental conditions. Solid-earth processes that affect the life-supporting charac- teristics of the global environment, especially those processes (e.g., volcanic eruptions) that take place at the interfaces between the earth's surface and the atmosphere, hydrosphere, cryosp here, and biosphere. The solar influence, including studies of the atmospheric re- sponse to changes in solar trends including variations in solar output and the earth's orbital elements. THE INTERNATIONAL GEOSPHER~BIOSPHERE PROGRAM Internationally, a new interdisciplinary program in which scien- tists from many nations and diverse disciplines can work together

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8 to understand the earth as an integrated whole is being planned to augment the ongoing efforts dealing with individual components of the earth system. The internationally defined objective of the Inter- national Geosphere-Biosphere Program (IGBP) A Study of Global Change, launched in 1986 by the International Council of Scientific Unions (ICSU, 1986), is to describe and understand the interactive physical, chemical, and biological processes that regulate the total earth system, the unique environment that it provides for life, the changes that are occurring in this system, and the manner in which they are influenced by human activities. Priority in the TGBP falls on those areas of each of the fields involved that deal with the key interactions and significant change on time scales of decades to centuries, that most affect the biosphere, that are most sus- ceptible to human perturbation, and that most likely lead to predictive capability. Implementation of the IGBP clearly calls for interdisciplinary, international research on an unprecedented scale. The success of the program will depend on the ability to document global change through long-term and sustained measurements of key variables in the earth system through an expanded space- and ground-based com- posite observing system. Modeling global change, a critical element of the program, calls for extended research by interdisciplinary teams employing advanced computational capabilities. Thus implementa- tion of the program requires a Tong-term political commitment to develop the scientific basis upon which policy decisions can be made. The operational framework for the IGBP must include investiga- tion and understanding of phenomena of time scales both shorter and much longer than the decades to centuries scale for which predictive capability is needed. Studies under the World Climate Research Pro- gram of the response to the short-term phenomena of E} Nino, for ex- ample, provide information about the modes and rates of response of the biota to changing environmental conditions. Long-term phenom- ena revealed in the record of the past provide essential background against which these more immediate changes can be evaluated. Sim- ilarly, although the focus of the program is on global scales, it must include those regional-scare studies that are needed both to under- stand the whole-earth system and to anticipate significant regional impacts of global change.

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9 The international scientific community is currently engaged in the preparatory phase of the IGBP under the guidance of the ICSU Special Committee for the IGBP. During this period, the program's goals and research components will evolve and-come into focus. Some operational elements of the TGBP have already been initiated, and others will be implemented as planning is completed and funding becomes available. The program is expected to be fully operational in 1992. The U.S. initial contributions to the IGBP, discussed in this report, together with U.S. contributions to related ongoing programs, will form part of this evolving international effort. OBJECTIVES AND ORGANIZATION OF THIS REPORT This report specifically proposes a limited number of early U.S. initiatives, based on the internationally defined goals for the IGBP, that wiD contribute significantly both to our national interests and to the IGBP. The proposed initiatives build on the several ongoing national and international programs addressing problems of global change relevant to the IGBP, notably the projects organized under the World Climate Research Program and the U.S. National Climate Program. The proposed initiatives are designed to supplement such existing efforts, not to supplant them. In formulating its recommendations, the committee had no in- tention of constraining either the IGBP or the broad U.S. program of research in the area of global change to only these specific early initiatives. These areas for initial focus are intended to provide a framework for early U.S. contributions to the IGBP rather than to include all research that will ultimately need to be carried out under the IGBP. The appropriate content and priorities of the broad U.S. effort on global change and the specific U.S. contributions to the IGBP wiD continue to be the subject of review and assessment by the committee. The specific purposes of this report are as follows: . to articulate a number of important key issues and inter- actions that characterize global change in the geosphere-biosphere system on time scales of decades to centuries; ~ to identify the knowledge that is the most urgently needled to improve un(lerstanding of those issues and interactions; an(1 · to formulate initial priorities for initial U.S. contributions to the [GBP, recognizing the contributions of other ongoing and proposed programs.

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10 Part ~ of the report constitutes the committee's findings, while Part I] presents a group of background papers developed by working groups under the coordination of members of the committee. These papers were prepared in workshops arid consultations organized by the committee, and they discuss research needs from five perspectives on the earth system: climatic and hydrologic systems, biogeochemical dynamics, ecological systems and dynamics, human dimensions of global change, and earth system history arid modeling. These papers provide a more complete indication of the range of issues considered by the committee in reaching its conclusions. Following this Introduction, Chapter 1 of Part ~ puts forward specific recommendations for the initial U.S. research contributions to the IGBP, based upon the background papers and the committee's analysis of scientific needs and gaps in existing efforts. Chapter 2 discusses supporting needs for program development, including Tong- term measurements, information systems, and management mecha- nisms. REFERENCES International Council of Scientific Unions. 1986. The International Geospher~ Biosphere Program: A Study of Global Change. Report No. 1. Final Report of the Ad Hoc Planning Group. ICSU 21st General Assembly, Bern, Switzerland, September 14-19, 1986. Earth System Science Committee. 1988. Earth System Science: A Closer View. National Aeronautics and Space Administration. Committee on Earth Sciences. 1988. Information for CES Meeting 4, June 23, 1988. Federal Coordinating Council for Science, Engineering, and Technology. Washington, D.C. \