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. 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. [Water, air, and soil pollution.; v70; 615; 1993.] [Journal of the Optical Society of America B; v10; 145; 1993.]