The trace gases known as greenhouse gases include water vapor. Water vapor is the most abundant of these gases. Water vapor also is perhaps the most dominant of all the trace gases because of its composition. Water vapor is essentially just H20--water--in a gaseous state.
Water has the ability to occur as a solid, liquid, and gas. As a solid, ice, as a liquid, oceans, and as a gas, clouds or water vapor. This ability enables water vapor to function as a very efficient feedback loop. Ice melts turning to water, water evaporates turning to clouds at high altitudes, clouds turn into rain, rain forms as ice at the poles and the cycle repeats as the environment warms. Water vapor creation is a natural cycle as opposed to some CO2 which is man made. Both water vapor and CO2 are greenhouse gases in that they retard the return of the radiation from the sun by forming a high altitude “blanket”.
Unlike CO2 which can be added to the atmosphere by way of natural phenomenon such as volcanoes, water vapor is is dependant on temperature to become a greenhouse gas by means of evaporation. The evaporation rate is tied to the ocean and near surface air temperatures. If extra water is added to the atmosphere by means of evaporation it condenses and falls back to the surface as rain or snow. On the other hand if all the moisture was pulled out of the atmosphere there would be no rain (drought).
The problem with water vapor and CO2 is one of balance. Increases in either or both warms while a decrease results in cooling. Since water vapor is primarily driven by evaporation, the ocean surface area is the primary driver. Jeff Goodell, in his excellent book “The Water Will Come”, addresses the problem of rising sea levels and realistically concludes that in eighty years the oceans will rise a minimum of six (6) feet. An increase of that nature will increase the surface area available for evaporation to an enormous amount. The increase in water vapor this would create will increase global temperatures to a level that many of today's creatures could not survive.
Things get worse when one considers that the atmospheric water vapor can retard the disbursement of CO2 by keeping it at lower elevations thereby increasing its capacity to increase surface temperatures while more CO2 is still being introduced into the atmosphere. The raw power of water vapor is perhaps better understood in a more familiar circumstance other than the atmosphere. Since @1750 and the start of the “Industrial Revolution” until the middle to late twentieth century nearly all machinery was powered by steam (water vapor). This water vapor heated homes, generated electricity, drove locomotives, and even some automobiles.
Today this water vapor albeit in a modified form is still a force to be respected and hopefully its influence on the atmosphere better understood. As alluded to earlier this greenhouse gas is the most abundant of all the trace gases. The climatic influence of water vapor demands more attention both on a scientific and secular level. Everyone is not a “Bill Nye the Science Guy” but all should become more attuned to our surroundings.