(Key for reading the diagrams: an arrow pointing up = increase; an arrow pointing down = decrease; a horizontal gray or curved blue arrow = causes)
Our burning of coal and oil releases CO2 which traps heat in the atmosphere. That extra heat puts more water into the atmosphere in two ways: the warming accelerates the evaporation of surface waters and, also, as the air warms, it holds more water – thus creating a positive feedback “loop” between water vapor and temperature, initiated by an increase in atmospheric CO2.
As the increase in atmospheric CO2 increases air temperature, it promotes the thawing of the permafrost (frozen ground in the tundra) which contains large quantities of CO2 from the bacterial decomposition of previously frozen vegetation and animal life. Briefly, any increase in atmospheric CO2 leads to an increase in temperature which leads to further increase in temperature due increase release of CO2 from the thawing permafrost – thus creating a positive feedback “loop” between increased atmospheric CO2 and temperature.
A related feedback loop from the warming atmosphere and the thawing of the permafrost is the release of previously frozen methane into the atmosphere. Methane traps about 30 times more heat than CO2, although it stays in the atmosphere for on the order of decades as opposed to centuries for CO2 -thus atmospheric warming initiates a feedback loop involving previously frozen methane.
Another feedback loop involves the release of methane from the deep sea beds. At sufficient depths, large amount of frozen methane are stored on the sea beds as methane clathrates – frozen clumps of methane. But as the atmosphere and, hence, the seas warm, they will eventually melt the clathrates which will escape into the atmosphere, further warming the atmosphere – thus atmospheric warming initiates a feedback loop involves the release of previously frozen methane clathrates.
A different type of positive feedback loop coming into play as the atmosphere and bodies of water warm involves the melting of the north polar ice (and land glaciers) that reflects 90% of radiant energy to expose water that absorbs 94% of the solar energy and thus increases warming which in turn reduces arctic ice and so on. The same sort of “decreasing reflectivity” loop is occurring where land ice glaciers are melting and exposing much more heat absorbent surfaces which in turn increase atmospheric warming and so on.
Another different kind of positive feedback loop coming into play as the earth warms is the decline of forests which absorb CO2 from the atmosphere , i.e. constitute CO2 “sinks”, reducing warming, because (i) of die offs once the temperature exceeds a species’ thermal maximum, (ii) increasing forests fires caused by increasing storms’ lightning – especially for dead forests, drought affected forests, and insect infestations that kill off forests or otherwise make them more vulnerable to burn more easily.
A unique case of a warming feedback loop promoting forest decline that can cause rapid, dramatic warming involves warming to a level that will result in the collapse/disappearance of the Amazonian forest and release of CO2 because of increased bacterial decomposition at the “floor” of the great forest. The Amazon rain forest is such that it fosters its own precipitation level to sustain the forest. As warming increases, it reduces the rainfall in the Amazon and forest will, effectively, begin to dry out and take less CO2 out of the atmosphere. When temperature has increased enough the Amazon rain forest (and great CO2” sink”) will collapse and the warmed soil and bacterial decomposition will yield an amount of carbon (CO2) greater than that in all living vegetation.