The snowball effect

Technically, it's a positive feedback loop. Say A acts on B and likewise, B acts on A. So, if A goes up, B does, which in loops back, increasing A. The cycle keeps continuing until either A or B max out or an external force quells both.

This is the opposite of the negative feedback loop, where A goes up if B goes down and vice versa. Whereas negative loops are self-correcting and are stable, positive loops go out of control. This is important because small changes in this type of system has massive impacts as even small fluctuations are magnified.

This has many implications:

Snowball Earth:
If a natural disaster such as a volcanic eruption or a meteor impact released a large cloud of obscuring ash, it would block sunlight and lower the temperature of the Earth. Fluctuations in the Sun's energy output or changes in methane and carbon dioxide levels would also have had the same effect.

This is believed to have actually happened, roughly 750 million years ago.

Ice, normally contained at the poles, then advanced towards the equator. As more area froze over, it was changed from dark earth and water to white ice. Since white ice reflects heat better than dark earth and water, the more the ice advanced, the less heat the earth would get. This would make even more ice form, and the cycle continued. This eventually spiraled out of control until the entire earth was frozen in a snowball.

Explained by this BBC video, the second of the series Horizon:




Butterfly Effect: Commonly known as the chaos theory, whose most commonly-known example is how a butterfly flapping its wings above the Atlantic could, after a series of magnifying events, trigger a

Cascading Failure: This was the cause of the Great Lakes-Northeast American Blackout of 2003. Because of a power flow monitoring failure and a human operator problem, a generating plant was shut down. This increased the load put on other transforming stations, transmission lines, and plants. As more and more failed, even the best-maintained plants could not handle the load, resulting in the failure of the entire system and the blackout.

Public Panics: The Salem Witch trials, for example, were started by a small group of accusing girls. The accused, in order to save their own hides, accuse others. This spreads until nobody feels safe and is in a constant state of panic.

Disparity in Wealth: Once someone reaches a certain wealth threshold where all basic needs are fulfilled, he can begin investing. Once he begins investing and trading stocks, he can make even more money, depending on the profits. With this, he will invest even more and earn even more to continue the cycle. Now, roughly the top 10% of the world controls 85% of the world's wealth.

Traffic: A traffic jam sometimes begins not with a physical obstruction like a crash, but just because of normal driving behavior. If there is a moderate stream of cars on the road, then the act of one person suddenly swerving can trigger a shockwave that ripples backwards to the other drivers. The car immediately behind the swerver slows down to avoid hitting the swerver. In turn, the next car does the same, and so on.



Economic Fluctuation: Mass sellings such as the Black Tuesday one that was the precursor to the Great Depression are often triggered by chain-reaction selling. As prices drop, people see that they're losing money and sell to cut losses. This drops the price further, which causes others to sell. Paradoxically, this is a positive feedback loop although it works in a negative manner.