Positive Feedback: The 1974 Dr. Who serial, Planet of the Spiders, revolves around “positive feedback.” Dr. Who (Jon Pertwee) warns the evil Spider Queen not to complete a lattice of crystals on her web. She believes doing so will increase her power. The Doctor tells her this is positive feedback, but, of course, she doesn’t listen, and kablooey! The Doctor, mortally wounded, escapes, and regenerates as Tom Baker.
We recognize positive feedback as the electronic shriek when a microphone picks up small noises, feeds them through the speaker, and re-amplifies it again and again. The phrase “positive feedback” is often misused for the psychological phenomenon of “positive reinforcement.” Systems thinkers use the electronic phenomenon as a metaphor for scenarios in which an intensified effect results in further intensity.
Climate theory uses examples of positive feedback. Global warming results in less high-albedo polar ice, causing more solar radiation to be absorbed and more warming. Warming melts permafrost, releasing methane, and a potent greenhouse gas is released.
In economics, concentrated wealth grants greater ability to gain wealth via access to investment opportunities, higher returns, and the ability to shape the financial and political systems. Exponential growth is a special case of positive feedback. Typical examples are compound interest and population growth.
Thomas Malthus, an English economist at the turn of the 19th century, predicted that exponential growth would eventually doom humanity. He claimed that agricultural production could only increase linearly, acre by acre, while human population would increase exponentially, outstripping our ability to feed ourselves.
World population is more than seven-and-a-half times Malthus’ one billion. Hunger remains a problem, but we produce enough food for everyone, and some of us eat very well. Shortly after Malthus published his prediction, Justus von Liebig invented artificial fertilizer.
A century later, somebody figured out how to get fertilizer from natural gas, and hybridization increased yields again. Europe dumped surplus population around the world and used North America as its garden.
Extinction: Scientists estimate a background rate of one to five extinctions worldwide per year. According to the Center for Biological Diversity, species are disappearing at 1,000 to 10,000 times that. (The vague estimate is due to the fact that scientists don’t know how many species there are, and many tropical species are extremely local, so they can only guess at the losses.) There have been five mass extinctions— six, if you count the rapid species loss Earth is currently experiencing.
In the June 13 Atlantic magazine, paleontologist Doug Erwin disagrees with the idea that we are experiencing a mass extinction. He says those events were collapses in the network of life.
In fact, the majority of life—75 to 96 percent of species on Earth—disappeared. “I think that if we keep things up long enough, we’ll get to a mass extinction, but we’re not in a mass extinction yet, and I think that’s an optimistic discovery because that means we actually have time to avoid Armageddon.”
Ecology: Death implies life. Plants use sunlight to turn carbon dioxide into food, and their bodies become fodder for both prey animals—which become food themselves—and decomposers that turn plants into soil.
The idea that ecology is the food chain is too simple; organisms are more than idiot shmoos, turning into supper for their predators. Services like habitat, fertilization, and oxygenation are just the beginning of a list.
University of Washington researchers removed the top predator, a sea star, from an intertidal community of 15 invertebrates in Mukkaw Bay. Only eight species remained, possibly because the sea star had been responsible for clearing space for the lost species to live.
Carrying Capacity: In a finite world, there’s a limit to how many members of a species an area can feed and shelter. Isle Royale is a 210-square-mile island near Thunder Bay. Moose colonized it in 1908. There were no large predators, so the moose population grew rapidly until it overgrazed the island’s vegetation. The moose population crashed in 1930, and again in the 1940s. In 1948, wolves reached the island over ice, and stabilized the population.