Definition - What does Water Vapour mean?
Water vapour is the state of water when it is in the hydrosphere. It can be achieved by water evaporation or boiling of water or by sublimation of ice. Water vapour is the most dominant of greenhouse gases. In fact, 95% of greenhouse gases are water vapour. Increased levels of carbon dioxide increase water vapour, which leads to warmer temperatures.
Safeopedia explains Water Vapour
Water vapour creates what is known as a positive feedback loop, making temperature changes larger than they would be otherwise. The amount of water vapour in the atmosphere exists in direct relation to the temperature. When temperatures increase, more water evaporates to become water vapour. As water vapour is a greenhouse gas, the increased amount of water vapour causes the temperature to increase.