Thinking in systems: loops, feedback and surprises

A system is a group of parts that work together to do something. A bike, a beehive, a school and a river are all systems. Systems thinkers don't just look at the parts. They look at the connections between them.

In, through, out

Feedback loops

A feedback loop happens when an output comes back and changes the input. A heater thermostat is a simple one: when the room gets warm, it switches the heater off; when it cools, it switches back on. That kind of loop keeps things steady.

Some loops make things run away instead. In a fish tank, too much food makes waste, waste feeds algae, algae uses up oxygen at night, fish get stressed and eat less, so even more food rots. Spotting runaway loops early is a big part of looking after any system.

A story from a real garden

A small aquaponics system at a community garden had been healthy for 14 months. A volunteer read that plants like slightly sour water, so they added a little vinegar every day. Over a week the water became too acidic, the bacteria that clean the water stopped working, poisonous ammonia built up and the fish began to suffer. The helper meant well. The system couldn't cope with a small change repeated every day.

Fast and slow systems

In a garden, a mistake in autumn might not show until spring. In aquaponics, a mistake on Monday shows by Friday. That's why it's a great teacher: you can see cause and effect while you still remember what you did.

Closing loops

In nature, one living thing's waste is another's food. Designers who copy this idea try to close loops: fish waste feeds plants, food scraps feed worms, roof water feeds the garden. Less waste goes out and fewer resources have to come in.