Earth System Science is a relatively new field of study that focuses on the operation of the whole Earth, including the atmosphere, hydrosphere, biosphere, and geosphere. These four spheres can be thought of as four machines or systems that are connected together to make one larger machine -- the whole Earth system. Earth System Science is especially concerned with the interactions between these different spheres and how these interactions control the global climate. This field of study incorporates and integrates material from traditional geology, meteorology, oceanography, ecology, atmospheric chemistry, and other fields.

Why has this new field of study has emerged recently? There are perhaps two related causes: 1) a growing sense of urgency to understand the dynamics of the global climate system; and 2) the rapid advances in computing and satellite technology that enabled us to observe and model the planet on a global scale. Why the sense of urgency to understand the workings of the climate system? Observations of the change in atmospheric composition (ozone depletion and CO2 increase) and rising global temperatures indicate that we are altering the global climate system, possibly with serious consequences. If we can understand the climate system, we can make good predictions about how it will change in the future, which will help us to decide how we need to change our behavior and what we need to prepare for in the future.

Because of the integrative, cross-disciplinary nature, Earth System Science demands a broad, holistic view of our planet and requires collaboration and communication between disciplines that were traditionally somewhat isolated. Isolated, reductionist thinking, in which you focus in on some small detail, is clearly important to the development of our knowledge, but by its very nature, this mode of thinking cannot illuminate the interconnections that are so important to the operation of the whole Earth system. The holistic view in no way dismisses the very careful, detailed studies that have taken place within all of the sub-disciplines encompassed in Earth System Science; instead, it builds on this accumulated knowledge and attempts to understand how it all fits together.

Earth System Science also involves some exciting challenges -- we need to cultivate a broad and deep understanding of all of the sciences. We also need to develop a grasp of how to analyze the behavior of systems that involve important interconnections -- this leads us to computer modeling which can range from the fairly simple versions explored in this book, to models that push the computing capabilities of the most powerful supercomputers.

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