Much of the current research on global environmental change adopts an earth system science perspective. This perspective involves the recognition that the earth's oceans, land, and atmosphere constitute an intricately coupled system with its terrestrial and marine biota, and employs an interdisciplinary and integrative approach to studying its components, their interactions and systemic change and variability over time. Definition, characterization, and understanding of GEC are contingent upon spatial and temporal scale, since earth system processes span a range of such scales.
For instance, plate tectonic movements occur over large spatial extents (tens of thousands of kilometers) and long time scales (millions of years). On the other hand, seasonal variations in primary productivity in a temperate deciduous forest biome occur over a spatial extent of hundreds of kilometers and relatively short time scales (months). The definition of a system's mean behavior depends upon the choice of spatial and temporal scale over which to average that behavior; thus affecting conclusions about system change or variability. A change in a system is generally perceived as unidirectional, sometimes irreversible, whereas variation implies some form of oscillation or fluctuation around a mean value. Systems differ with regard to their stability (ability to retain system characteristics such as structure and function in the face of an externally induced perturbation), or resilience (a measure of a system's ability to return to its initial state following a perturbation). In addition, systems may be characterized as approximating an equilibrium state (homeostasis), typically involving negative feedbacks, or a non-equilibrium state characterized by stochastic and/or nondeterministic processes of change.
The International Geosphere-Biosphere Program (IGBP) was founded in 1986 by the International Council of Scientific Unions (ICSU). The IGBP constitutes an international, interdisciplinary scientific approach to pose and answer questions about the nature of the earth system and its biogeochemical cycles, its structure, function, and response to human-induced alterations (forcing functions); whether we can or should return to the system state preceding current episodes of human-induced system forcing, such as greenhouse-gas emissions led climate change; and how human societies and economies can achieve such challenges. The IGBP helps coordinate and synthesize research that elaborates key aspects of the earth's hydrological and biochemical cycles, quantifies rates and patterns of change within them and identifies critical drivers and consequences of those changes.
The meaning of cities in a global and increasingly digitized age is one of the subjects we confront as we enter the new century (Friedmann 1986; Castells 1989; Short and Kim 1999; Valle and Torres 2000; Sassen  2001; Thrift and Amin 2002; Drainville 2004). Yet the understandings and the categories that still dominate mainstream discussions about the future of advanced economies imply that in a global digital age, the city has become obsolete for leading economic actors; this would also imply the obsoleteness of the city as a site for researching major nonurban dynamics. We need to subject these notions to critical examination. There are at least two sets of issues that need to be teased out ...