Natural Systems

• Positive Feedback = A cyclical sequence of events that amplifies or increases change.
• An example of positive feedback in the water cycle is that rising sea levels can destabilise ice shelves, increasing the calving rate and leading a further rise in sea levels.
• An example of positive feedback in the carbon cycle is that increased temperatures cause thawing of permafrost, this releases trapped greenhouse gases, enhancing the greenhouse effect and raising temperatures further
• Negative Feedback = A cyclical sequence of events that damps down or neutralises the effects of a system
• An example of negative feedback in the water cycle is that an increased surface temperature leads to an increase in ocean evaporation, this increases cloud cover which reflects solar radiation and results in cooler tmperatures
• An example of negative feedback in the water cycle is increased atmospheric CO2 leads to increased temperatures which promote plant growth and rates of photosynthesis, which in turn, removes CO2 from the air.
• In its entirety, the water cycle system is a closed system – water is not lost to or gained from space. However, at a local scale, such as a drainage basin, it is an open system.
• As this is the global carbon system, it is a closed system – there are no inputs to or outputs from the system as a whole. At a local scale, such as a forest, it is an open system with both inputs and outputs.
• Dynamic Equilibrium = A state of balance between inputs and outputs in a system
• Cascading system = When the outputs of one system become the inputs for a subsequent system