As air temperatures increase, evaporation increases. Warmer temperatures also increase the capacity to absorb water vapor. More water vapor in the atmosphere accelerates the greenhouse effect. As temperatures increase further, more water vapor can enter the atmosphere, causing temperatures to increase even more. This is an example of a (n)

positive feedback loop

Explanation:

Positive feedback loop is a occurrence wherein output of the system amplifies that particular system. The effects of particular change on the system include the increase in magnitude of that change.

Thus, in the mentioned case in which the rate of evaporation of water increases on increasing temperature which further increases the rate as warmer temperature causes the greenhouse effect and which facilitates more evaporation.