A feedback loop is any initial process that triggers a change that in turn influences the initial process. The feedback loop is considered "positive" if it increases or enhances the initial process, "negative" if it lessens or negates the initial process.
In the case of climate change, there's nothing "positive" about positive feedback loops. For those folks out there who weren't paying attention in 7th grade science, the earth is a very delicately balanced system of systems. Any disruption in one system (in this case, the carbon cycle) inevitably inpacts other systems - sometimes in ways that are easy to predict, other times in ways that are freakishly complex. This is the main reason scientists can't tell us how quickly climate change is going to happen: while they have a pretty good handle on how much carbon dioxide we humans will be producing in the future, they really have no idea of the extent to which feedback loops - some already identified, some only just now being studied, some yet to be discovered - are going to exacerbate and hasten global warming. What they can, and are, telling us, however, is that the more they learn about feedback loops, the more frightening the climate change prognosis becomes.
Without further ado, following are some of the more significant positive feedback loops scientists have thus far identified, a list that I'll continue to add to as new research becomes available.
- Warmer temperatures will cause people to use more air conditioning, the emissions from which will hasten climate change.
- Melting icecaps will result in less reflective surface on earth (an effect called ice-albedo), causing the earth to absorb increasing amounts of heat, which will hasten climate change.
- Melting ice forms rivers of water that erode through the glacier over/through/under which they flow, further hastening the melting rate of glaciers. Fewer glaciers = less light-colored surface to reflect light = faster climate change (per #2)
- Droughts will cause more forest fires, the smoke from which will hasten climate change. Oh - and ash from the fires will cause the earth to darken, which will cause the earth to absorb more heat (see #2), which will also hasten climate change
- Everyone knows that trees photosynthesize during the day (absorbing carbon dioxide & releasing oxygen - GOOD!) then during the night hours use the energy they've created to grow and do other tree business (absorbing oxygen & releasing carbon dioxide - BAD!). Recent research suggests, however, that when trees become too stressed - because of excess heat, for example - they reduce the amount of time they spend photosynthesizing and increase the amount of time they spend using energy ... which returns carbon dioxide into the atmosphere, which will hasten climate change
- Cold water does a better job of retaining dissolved gasses than warm water. At ocean and freshwater temperatures increase, they will release stores of dissolved methane and carbon dioxide, which will hasten climate change. The converse of this is also true, by the way - as ocean waters warm, they will be able to absorb smaller amounts of carbon dioxide than in past ... further hastening climate change.
- Enormous amounts of carbon dioxide and methane are stored in tundra permafrost. As permafrost ice melts, quantities of methane and carbon dioxide will be released into the atmosphere, hastening climate change. Oh, and warming temperatures are causing a "baby boom" of microbes that are degrading the permafrost even more swiftly, further hastening climate change.
- Most people are aware that, when it comes to slowing climate change, more trees is a good thing because they absorb carbon dioxide during the process of photosynthesis (#5). What many people don't remember is that during the process of photosynthesis trees also release excess water vapor in a process known as transpiration - evaporation of moisture from trees. Interestingly, most of the rain that falls in rainforests such as the Amazon isn't actually produced by evaporation of groundwater but by transpiration. Therefore, as droughts kill trees in the rainforest, even more severe droughts are triggered due to reduced transpiration, which will kill more trees ... hastening climate change
- Warm temperatures hasten the decomposition of vegetable matter (ex: peat), which will increase the amount of carbon dioxide entering the atmosphere, thus hastening climate change
- Warmer temperatures cause more evaporation, which causes more water vapor to enter the atmosphere. Alas, water vapor is a greenhouse gas, so this will hasten climate change.