The growth is the Earth System Science (ESS) approach has accelerated in the last 20 years. A diagram indicates how different disciplines and specialists are involved in its activities. This diagram also lists the fields of science and technology that play roles in ESS. The various natural phenomena characterizing the Earth system tend to occur over different lengths of time (time-scale effect). These may be cyclic, as illustrated by the water cycle.

### Earth System Science

The evidence continues to pile up regarding Man's impact on the natural world and its environment. Recently, an international group of scientists prepared and published a global map which they titled "The Human Footprint" that plots biome disturbance at the present time. They based this map (GIS-like in construction) on four prime variables: 1) population density; 2) land transformation; 3) human access; 4) power infrastructure. Satellite data were included in these assessments.

As you might expect, Europe, India, eastern China, eastern United States and the coastal areas of South America show the largest biome modifications (in the 40 to 60 range). The minimal damage (greens; low values) in the Australian continent reflects the continuing tendency for its population to reside close to the coasts. Nevertheless, the fact that much of the world's land surfaces have already been damaged (whether this is reversible is still an unsettled question) places the focus on what we must consistently monitor if we conclude that it is necessary to control future human activities to moderate or even restore the natural biomes that are beneficial to mankind.

Clearly, we need some answers, if we are to understand our planet's physical and biological phenomena and how they interact, and to determine human contributions to global change phenomena. We need this information so we can make decisions to reduce any detrimental changes we cause, or to adapt to circumstances we cannot change. We must collect data that allows us to understand the basic forces and rhythms of our planetary system, and to distinguish global changes due to natural effects from those due to human activities. This global analysis, in turn, requires us to acquire data about virtually every aspect of the Earth system over a long enough period that we can see contributions from long-term phenomena (e.g., an 11-year Solar cycle) and trends. Then, we must use the data to generate information that helps planners and policy-makers to ensure a sustainable environment for all of us.

The evolution of the new field of Earth System Science (ESS) over the last twenty years is largely the logical consequence of these factors:

(1) The growing interest in and concern for the environment

(2) The increasing awareness that biological and physicochemical Earth processes and activities often are mutually interlocked or influential, so that each controls the other to some extent

(3) The recognition that many key processes act on a regional, and often global, scale and we must examine and interpret them at those levels

(4) The realization that many scientists work in fields and subfields in the Earth sciences that are interrelated and share similar study topics and methods, and hence they would benefit by working together in teams

(5) Technology advancing to allow global monitoring (from space).

Its hallmark, then, is that it is an interdisciplinary (multidisciplinary) scientific endeavor made by specialists in aspects of Earth science - geologists, oceanographers, meteorologists, ecologists - working together with biologists-botanists-agronomists, chemists, and physicists to investigate a wide range of physical and biogeochemical activities that affect the environment (including resources). They do this by treating Earth as a complex but integral system of entities. They concentrate on its functions from a total, or full-Earth, vantage point, i.e., primarily from the global perspective. As now developed, Earth System Science works with the knowledge associated with three major, natural, dynamic, operations: the hydrologic cycle, the physical climate system, and biogeochemical cycles. To the above list, comprised of scientists and technologists, can, in fact, be added such contributing professions as sociologists, economists, and legal specialists.

A prime goal for integrating the contributions by the various disciplines in the above diagram is to determine how the earth system interacts when viewed from differing perspectives. Put another way, Earth System Science studies relevant components, interactions and exchanges, and ecological ramifications among the following arbitrary "spheres," each defined by its own sets of characteristics and internally-related activities and subsystems: Geosphere; Ocean (sphere); Hydrosphere; Atmosphere; Cryosphere; and Biosphere.

16-9: Many universities still don't offer courses called "Earth System Science". What two courses taught for decades in the past come closest to ESS in content? ANSWER

In keeping with the Huttonian Doctrine ("The present is the key to the past" - and almost certainly the future as well [writer's addition]), many of the processes have operated continuously at time scales ranging from minutes to vast millenia. Most of these processes also perform at different spatial scales, ranging from local to subcontinental or over vast oceans. For the atmospheric system, the range is at a global horizon. We synopsize this idea in this generalized space-time diagram:

This diagram suggests that we must study some processes over relatively small regions and short time frames, whereas others require worldwide monitoring over extended periods (often beyond a human life span). Nevertheless, even for the latter, we can glean useful information from determining the magnitude and frequencies of changes within the processes, as they proceed through time and shift in space. Changes affecting large segments of, or even the entire planet will likely have profound effects within the global system.

16-10: What parts of the above time-size plot are not especially favorable to satellite observations? ANSWER

Primary Contact: Nicholas M. Short, Sr. email: nmshort@ptd.net

Dr. Mitchell K. Hobish, Consultant (mkh@sciential.com)