Evaporation from large bodies of water, such as tropical seas and lakes is one of the sources of water vapor in the air. Other sources include the natural biological processes of plants and animals, such as respiration and transpiration.
Atmospheric water vapor can also result from human activities, such as farming, the watering of lawns and landscaping. Additional sources of water vapor include man-made geographical alterations, such as the evaporated water from canals, artificial lakes and reservoirs behind dams.
Water vapor is also a by-product of combustion; the burning of natural gas, petroleum and other fossil fuels also contributes to the amount of water vapor in the atmosphere. Extraction of water from underground sources such as aquifers for drinking and irrigation is another anthropogenic source of water vapor.
Water vapor is the Earth’s most abundant greenhouse gas, accounting for over 95% of the greenhouse effect, according to NOAA. Although this gas is so critical to the future of the Earth’s climate, very little can be done to alter the Earth’s natural water cycle and significantly change the amount of water vapor in the air. All human contributions to atmospheric water vapor account for a mere 0.001% of the total amount in the atmosphere.