The increase of the input into a system, which produces a negative or a positive output in a system of interlocking components; the return of a part or the effects of the output to the input. A proposed positive feedback cycle involves the outgassing of carbon dioxide from the planet's oceans: Since CO₂ solubility in water decreases with temperature and since CO₂ is a greenhouse gas, a positive (and possibly runaway) feedback cycle might involve the following: increased greenhouse warming of the atmosphere by IR absorbing CO₂ in the gas phase--and the subsequent heating of the oceans--could increase the amount of carbon dioxide released into the atmosphere from the oceans. This might thereby increase greenhouse warming, which would, in turn, again heat the atmosphere and the ocean, etc. This is an amplification of the input: positive feedback: leads to more warming. Though the process is no doubt more complicated than this, a runaway greenhouse effect is usually given as the reason for Venus' high surface temperatures so a planet-wide process of this type is not unknown.

Conversely, a negative feedback cycle might consist of the increase in release of dimethyl sulfide (DMS) by ocean surface microorganisms whose population is increased by ocean warming. DMS oxidation in the troposphere leads to sulfate aerosol formation which act as cloud condensation nuclei in the marine troposphere. Increased CCN would increase cloud albedo which increases reflect incoming solar radiation, thereby cooling the oceans. This is an dampening of the input: negative feedback: leads to termination of the original warming.