Positive feedback

Positive feedback is a process in a cybernetic system where a change in one property of the system triggers changes in one or more other properties which, in turn, cause the first property to continue changing in the same direction, usually at an accelerating rate. Positive feedback can often lead to a system "getting out of control" and is thus often referred to as a "vicious cycle" or "death spiral." However, as Paul Krafel and others have shown, positive feedback can also operate as an Upward Spiral, in the direction of increasing ecosystem health and the number and diversity of organisms in a region.

An example of a positive feedback that is harmful to life can be found at Earth's north pole, where increasing atmosphere and ocean temperature due to the global climate crisis is causing a reduction in the extent of the sea ice cover. This allows more sunlight to be absorbed in the arctic region, because dark seawater absorbs heat far more readily than white ice, which reflects most sunlight back to space. The warmer seawater heats both the air above it and the sea ice, melting even more of it, and so on. This "downward spiral" explains why scientists originally drastically underestimated the speed at which the northern ice cap would disappear, and is also a major factor in why the Arctic is warming much faster than other parts of the world. An example of a positive feedback that is beneficial to life is the process of ecological succession in an alpine ecosystem, as described in Krafel's movie The Upward Spiral. First, lichens grow on bare rock, capturing a small amount of the snowmelt that flows rapidly over the surface and reducing its speed a little. As more lichens grow, and some of them decompose to form soil, streams slow down further and the soil absorbs more moisture, enabling it to support more advanced forms of plant life. This process of slowing the water down continues as plants develop deep root systems, which hold soil in place and slow down the flow of groundwater, and drop leaves or needles into streams, often accumulating at narrow places in the watercourse to form dams and pools where the water moves very slowly indeed. The basic principle is that slower-moving water can more easily soak into the soil, nourishing more plants, which slow the water more. The plants then serve as the basis of an ever-growing food web.