The current scientific and political interest in global change has had a number of important intellectual consequences, evident in the literature reviewed in this report. First, interest in the existence and mechanisms underlying low frequency behavior of the earth system has emerged from specialized communities within the climate, ocean, geological, and ecological sciences and has become a major activity within and among those disciplines. The ``paleo'' subdisciplines are now in the forefront of scientific discourse in the earth and ecological sciences. Second, a dominant paradigm during the 1960-1980s, for studies of processes in the above disciplines, often assumed that system components were in actual or aggregate equilibrium on timescales relevant to human concerns [e.g., Bormann and Likens, 1979]. Increasingly, process studies are being applied to understand the evolution of climate and coupled marine and terrestrial systems over time [e.g., Wang and Birchfield, 1992; Manabe and Stouffer, 1993; Archer et al., in press]. Finally, much of the low frequency behavior of the climate system arises from coupling of system components, such as the ocean and atmosphere or climate and the carbon cycle [ Wang and Birchfield, 1992; Delworth et al., 1993; Schimel et al., 1994]. The importance of atmosphere-ocean, atmosphere-biosphere, and physical-chemical-atmosphere coupling as drivers of low frequency variability and changes in the climate system has forced an ``interdisciplinary'' approach and in fact is resulting in a slow reorganization of the intellectual structure of the earth sciences, reducing the distinctions between atmospheric, oceanic, and hydrological sciences and including terrestrial and marine ecology as parts of the earth, and not just the life, sciences. These trends accelerated over the past four years and are likely to be dominant features of the earth sciences by the time of the next quadrennial report.
Acknowledgments. We thank Scott Doney and Jim McWilliams for explaining many issues related to modeling the thermohaline circulation. The authors were supported by the National Center for Atmospheric Research, NASA's Earth Observing System through an Interdisciplinary Science award to DS, and by the Climate System Modeling Program of UCAR, which is supported by the National Science Foundation and the Department of Energy. The National Center for Atmospheric Research is sponsored by the National Science Foundation.