- The Earth is very complex, so we try to simplify aspects to make links and components more understandable. The simplifications are called models, the Demographic Transition Model for population, and one type of model is a system:
- A system is a set of interrelated components working together towards a process.
- An input is the addition of matter/energy into a system.
- An output is the removal of material from the system.
- A store/component is a stationary part of the system where energy/mass is stored or transformed.
- A flow/transfer is a form of linkage between a store and another which involves the movement of energy or mass.
- Systems are made up of stores/components which have flows/transfers between them of the matter/energy.
- Most systems share common characteristics:
- Structure that lies within a boundary.
- Generalisations of reality.
- Function by having inputs and outputs of material which is processed within the components and is caused to change.
- Involve flow of the material between components.
- There are various types of system:
- Isolated system – no interaction with anything outside the system boundary.
- Closed system – transfers of energy both into and beyond the system boundary, but not a transfer of matter.
- Open system – matter and energy can be transferred across the system boundary into the surrounding environment.
- Cascading system – a chain made up of lots of open systems.
- A balance between inputs and outputs is referred to as dynamic equilibrium. At this point, the stores remain the same. If part of the system changes, like an increase in inputs without a change to outputs, the equilibrium is upset, and this is feedback.
- Positive feedback is when the effects of an action are amplified/multiplied by subsequent knock on effects such as a rise in global temperature warms the oceans, warmer oceans cannot dissolve gases as well, dissolved CO2 is released back into the atmosphere, so there is more in the atmosphere and it acts as a greenhouse gas, increasing global temperatures to a further extent.
- Negative feedback is when the effects of an action are nullified/eradicated by subsequent knock-on effects such as more use of fossil fuels releases more CO2 into the atmosphere which increases the global temperature.
- This leads to more plant growth, and the plants then use more CO2 which reduces the atmospheric levels of it, so temperatures cool.
- The Earth is a cascading system, with four main sub-systems; atmosphere, lithosphere, hydrosphere and biosphere.