Everything viable on this planet is in a feedback cycle: plants give us oxygen, we give them CO2; animals eat grass, fertilize the field, predators and prey adapt to keep each other from outstripping their food supply, and so on.
As the snow and ice retreat, the Earth's surface gets darker and absorbs more heat, warming the whole planet in a dangerous feedback loop where warming causes melting and melting causes warming.
Pushing the planet too far may cause a feedback loop just like when a loud speaker situated too near to a microphone causes the volume to rise uncontrollably.
Since low-level clouds tend to bounce sunlight into space and cool the planet, that amounts to a positive feedback that would accentuate global warming.
We could already be seeing feedback loops where the planet responds to climate pollution by releasing its own greenhouse gases, which accelerate the cycle ever faster, to catastrophic levels.
It is clear from the research that Earth's feedback systems kept the planet from plunging permanently into a snowball state, says geologist Alan Jay Kaufman of the University of Maryland, College Park.
In principle, the feedback system might spare the planet from a runaway greenhouse effect if the oceans take up enough carbon from the atmosphere.
It walks readers through the basics of the energy cycle on the planet before embarking on a deeper consideration of feedbacks involving clouds and other parts of the "earth system," as scientists call it.
The planet has remained comfortable ever since thanks to a geological feedback process, by which weather, oceans and volcanoes act as a thermostat.
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