concept

Positive feedback

A loop in which a change amplifies itself, driving the system further and further from its starting state rather than back toward it. Melt polar ice and you expose dark ocean that absorbs more heat and melts more ice; thaw permafrost and it releases greenhouse gases that thaw more permafrost. Positive feedback lies dormant until a threshold is crossed, then takes over and runs the system away toward a new state. It is the mechanism behind planetary tipping points - what turns a small warming into an irreversible flip. It is the opposite of negative feedback, which stabilises.