1309Bulletin of the American Meteorological Society1. IntroductionAs part of its strategic plan, the National Aeronau-tics and Space Administration (NASA) formulated thegoal of “utilizing the knowledge of the Sun, Earth andother planetary bodies to develop predictive environ-mental, climate, and natural resource models to helpensure sustainable development, and improve the qual-ity of life on Earth” (NASA 1998). We know now that,over geologic periods, the earth climate is governedby the interplay of two major cycles: the cycling ofcarbon through the earth atmosphere, terrestrial veg-etation, oceans, sediments, and lithosphere, and thecycling of water through the atmosphere, rivers, andoceans. The recognition of multiple linkages betweenthe earth’s physical environment and the biosphere isa discovery of the twentieth century, which led to thenew concept of earth system science. This new scien-tific paradigm is founded on the notion that the glo-bal earth environment can be understood only as aninteractive system embracing the atmosphere, oceans,and sea ice, glaciers, and ice-sheets, as well as marineand terrestrial ecosystems. The NASA Earth ScienceEnterprise (ESE) aims to obtain a scientific under-standing of the entire earth system, on a global scale,by describing how the system’s component partsevolve, how they function and interact, and how theymay be expected to change in the future.In its report Global Change Research Pathways forthe Next Decade (NRC 1999), the National ResearchCouncil (NRC) highlighted the complexity of earthsystem science and the multiplicity of interactionsbetween component processes. In drafting this scien-tific strategy for the U.S. Global Change ResearchProgram (USGCRP), the NRC identified a wide rangeof unsolved scientific questions, but also emphasizedthe need for a focused plan, concentrating researchefforts and resources on critical scientific problemsthat are most relevant to economy and national policyNASA Research Strategy for EarthSystem Science: Climate ComponentGhassem Asrar,* Jack A. Kaye,* and Pierre Morel+*Office of Earth Science, National Aeronautics and Space Ad-ministration, Washington, D.C.+Goddard Earth Sciences and Technology Center, University ofMaryland, Baltimore County, Baltimore, Maryland.Corresponding author address: Dr. Pierre Morel, GEST, Univer-sity of Maryland, Baltimore County, 1000 Hilltop Circle, Balti-more, MD 21250.E-mail: [email protected] final form 8 February 2001.©2001 American Meteorological SocietyABSTRACTThis paper describes the principles adopted by the NASA Earth Science Enterprise in formulating a comprehensive2002–2010 research strategy for earth system science, and outlines one component of this broad interdisciplinary pro-gram, focused on physical climate research. Before embarking upon topical discussions of each element of the program,the authors sketch NASA’s overall strategy for climate research and organize the main research thrusts according to alogical progression from documenting climate variability and trends in relevant climate forcing factors, to the investiga-tion of key climate responses and feedback mechanisms, consequences for weather and water resources, and climateprediction issues. The ultimate challenge for NASA’s earth system science program, a major contribution to the U.S.Global Change Research Program, is to consolidate scientific findings in the different disciplines into an integrated rep-resentation of the coupled atmosphere, ocean, ice, land, and biosphere system. The hallmark of NASA programs is in-deed the integration of observations, principally global observation from research and operational satellite andsurface-based observation networks, into consistent global datasets to support its scientific research programs and theverification of earth system model predictions against observed phenomena.1310Vol. 82, No. 7, July 2001issues. NASA’s earth science program is one of themajor components of the Global Change ResearchProgram (USGCRP 2000). NASA defined the objec-tives of its program by formulating a set of overarchingscientific questions (Table 1) that reflect the prioritieshighlighted by the NRC and also the nature of NASA’sspecific contributions to interdisciplinary earth systemscience research. NASA’s contribution includes aunique combination of research capabilities: space-based global observing systems and long-range air-borne observing facilities, integrated global dataanalysis and modeling programs, and the ability tofacilitate the development of applications to practicalproblems in food and fiber production, water and natu-ral resource management, natural hazard reduction,and other environment-dependent activities.The scientific questions formulated by NASA canbe envisioned as successive steps in a logical progres-sion from observation and scientific understanding toprediction:• How is the global earth system changing?• What are the primary forcings of the earth system?• How does the earth system respond to natural andhuman-induced changes?• What are the significant consequences of globalchange for human civilization?• What changes in the earth system will take placein the future?This conceptual approach applies in principle toany aspect of earth system science, but it is particu-larly relevant to the study of climate and climaticchange. The present paper focuses on two componentsof the ESE’s research strategy, the study of the globalwater and energy cycle, and the role of oceans and icein the climate system, addressing specifically the ques-tions italicized in Table 1. The other components ofthis interdisciplinary strategy—atmospheric chemis-try and its relation to climate, ecosystem and carboncycle research, solid earth science—will be addressedelsewhere.Information for global change research comes froma multiplicity of national and international sources,including research and operational satellite programs,as well as surface-based observations carried out byresearch institutions and government agencies. TheESE seeks the cooperation of these national and for-eign partners to maximize returns from its own scien-tific investments. In particular, the ESE activelycooperates with operational environmental agencies inthe United States and abroad to ensure the long-termcontinuity of key environmental measurements, andparticipates in related applied research programs suchas the U.S. Weather Research Program. Relevance tooperational