A lot of climate-change deniers will use that same old tired argument: “Listen, the climate has been changing ever since there was a climate to change. It’s bogus to think that humans have something to do with this.” Unfortunately, we either know of or have a pretty good idea of the forces at work during each period of historically great climate change. And we know of the force at work during this one–it’s us, and it’s not a topic for debate around the world. Only here in the United States is it a political card to play.
Positive feedback loops happen when a small force in a closed system eventually increases the magnitude of that same force. A popular example of this uses a group of cattle. When one cow starts running, a few more will. After a short period of time, the entire group of cattle will become panicked and start to run. That’s a positive feedback loop.
There are a number of these involved in climate change.
- Precipitation. We’ll start with a “negative” feedback loop, one that might actually reduce the warming trend. The warmer it gets, the more moisture gets sucked into the atmosphere. The more moisture there is in the atmosphere, the more rain we get. The more rain we get, the more plants grow. The more plants grow, the more carbon dioxide they release into the atmosphere. The more carbon dioxide is released into the atmosphere, the more the climate cools.
- Ice. This one’s a positive feedback loop. The warmer it gets, the smaller the surface area of the sea ice as it melts away. The smaller the surface area of the ice, the more light is absorbed by the ocean instead of reflected back into the atmosphere. The more light is absorbed by the ocean, the more sea ice melts. This positive feedback loop is why the arctic ice is disappearing so dangerously fast. It ends where it begins, only worse than where it started. Melting ice also releases methane into the atmosphere, making the problem even worse. The problem is that ice albedo is an example of a particularly powerful positive feedback loop. Not all are created equal.
- Deforestation. If we stopped deforestation, we might be able to create a negative feedback loop. The warmer it gets, the more precipitation there is, and the greener the forests become. That means more oxygen. But we keep devastating the rainforests, reducing overall oxygen production while increasing carbon dioxide production. Each of those trees stores carbon dioxide. We burn them, and it gets released. Boom.