ANSWER: A positive feedback mechanism is a process which is reinforced by other processes. A negative feedback mechanism is a process which is weakened by interactions among other variables. The water vapor-temperature increase process is a positive feedback mechanism. Assuming that the Earth-atmosphere system has been disturbed to the point that Earth has entered a slow warming trend, over the years the temperature slowly rises, and water from the oceans rapidly evaporates into the warmer air. The increased quantity of water vapor absorbs more of Earth’s infrared energy, thus strengthening the atmospheric greenhouse effect. This strengthening of the greenhouse effect raises the air temperature even more, which, in turn, allows more water vapor to evaporate into the atmosphere. The greenhouse effect becomes even stronger, and the air temperature rises even more.