1.2 SystemsIB Environmental Systems and Societies HL: Revision notes

A system is a set of interacting or interdependent components. A systems approach is a holistic way of visualising a complex set of interactions, in ecological and societal contexts, that can help in decision-making. The concept can be applied at a range of scales, from a puddle to the whole Earth.

In system diagrams, storages are usually rectangular boxes and flows are arrows showing the direction of movement of energy and matter. Flows are processes that are either transfers (change of location) or transformations (change of form or state).

Open systems exchange both energy and matter with their surroundings. Closed systems exchange only energy. Ecosystems are open systems; Earth is effectively a closed system for matter and an open one for energy.

The Earth is a single integrated system made of the biosphere, hydrosphere, cryosphere, geosphere, atmosphere and anthroposphere (human systems and activities).

Negative feedback occurs when the output of a process inhibits or reverses the same process, reducing change. An ecosystem, as an open system, normally exists in a stable equilibrium (steady state) maintained by negative feedback.

Positive feedback occurs when a disturbance leads to its own amplification, destabilising the system. Positive feedback loops tend to drive a system towards a tipping point: a point where a small alteration in one component has a large effect on the whole system, resulting in a shift to a new state.

A model is a simplified representation of reality. It can show how a system works and predict how it will respond to change. Simplification involves approximation and therefore loss of accuracy. Always say that a model is useful but limited.

Interactions between components can generate emergent properties, which are properties of the whole that no single component has.

Resilience is the tendency of an ecological or social system to avoid tipping points and maintain stability. Diversity and the size of storages contribute to resilience and affect the speed of response to change. Humans can reduce resilience by reducing storages and diversity, e.g. by draining wetlands or clearing forests.