Water Vapour Definition

by Laurent Cousineau
(Montreal)

Water vapour, also spelled water vapor, is the gaseous form of water.

In an environmental context, this term is used to refer to the water vapour present in the Earth's atmosphere.

Water vapour plays a key role in the natural greenhouse effect.

In fact, it is the most abundant greenhouse gas.

Notably, this natural greenhouse gas affects temperatures in the troposphere by means of cloud formation.

In effect, excess water vapour in the troposphere will condense to form clouds.

In turn, this condensed water vapour will fall as precipitation.

Water Vapour and Climate Change

Mankind does not significantly emit water vapour.

However, water vapour enhances the greenhouse effect via a positive feedback loop.

In other words, global warming will cause more water to evaporate into the atmosphere and since water vapour is a greenhouse gas, this will cause even more warming.

Therefore, if carbon dioxide increases the temperature by 1°C, this feedback mechanism will cause temperatures to rise by another 1°C.

In fact, when other feedback loops are also considered, temperatures may actually rise by 3°C for every 1°C change caused directly by CO₂.

Greenhouse Gases

• Carbon Dioxide
• Chlorofluorocarbons
• Hydrochlorofluorocarbons
• Hydrofluorocarbons
• Methane
• Nitrous Oxide
• Ozone
• Perfluorocarbons
• Sulfur Hexafluoride
• Water Vapour