The Earth's environment on a human time scale is changing due to both natural and human-induced factors. Environmental changes that are apparent to anyone who reads the newspaper include: global warming, ozone depletion, deforestation/desertification, decreased biodiversity/extinctions/ pollution, and reduction of natural resources.

This course provides a primer for trying to understand and assess environmental change. We want to understand why environmental variability occurs in natural systems, estimate what past environmental conditions existed and why they occurred, and ask what is in store for the future. An important added question is what portion of historic environmental variability is natural versus human-induced and what methods are available for remediaiton.

The Earth is an integrated dynamical sytem composed of four primary interlocking components: atmosphere, lithosphere, hydrosphere, and biosphere. At any location within this overall earth system we can define a local environment which describes the combination of physical, chemical, and biological factors that make up the local living space.

All of the components are dynamic in character; that means that they are always changing or evolving, never static or fixed. It also suggests that the components are interactive; as part of the overall dynamic character, each component influences and responds to changes in other surrounding components. This has resulted in a spectacular variety of Earth environments over the course of Earth history and it is a warning that the dynamical system we see today is not the least bit fixed or static.



The overall Earth environmental system is composed of interacting components. The state of the system identifies the current conditions of its components. An equilibrium state is one that is able to maintain itself for some time in the presence of interactions between the systems components. Couplings represent individual interactions between pairs of components..

The observed interactions can take several forms: control, simple dependency, or mutual feedback. The interactions also have several complications in the form of lags and buffers. Below we consider the roles of the various elements in the overall scheme of internal interactions.

Control/Dependence - Some Earth processes critically depend on other processes in a simple and direct manner. In reality, this is a very unusual condition, but, nevertheless, it is the simplest way to imagine Earth system interactions.

Feedback - Feedback in the Earth System implies that change in system A will cause change in system B which will, in turn, cause change in system A. If the feedback is positive, increases in system A will cause changes in system B which cause system A to increase further. This can cause a 'cascade' effect which leads to very fast, almost 'step' changes in the overall Earth system. If the feedback is negative, increases in system A will cause changes in system B which cause system A to decrease. Negative feedback helps to damp out variations in the Earth system.

Lags/Buffers - In many system interactions, variability in system A may be quite large without affecting system B. This could be due to buffering or sensitivity. Likewise, in some interactions variations in system A can occur quickly, but the response of system B may be much slower. This produces an observable lag.



Daisyworld is a simple model of a world environmental system which can be analysed and used to test interactions, feedbacks, and issues of stability.