Water Vapor, CO2, and Global Warming

Thomas Schueneman

Water vapor vs. CO2 and the greenhouse effect

In my discussions with people regarding climate change and global warming, I've found some confusion regarding the role that CO2 plays versus water vapor in the "greenhouse" effect.

In order to address this issue, I've done some further research on this particular aspect of greenhouse gasses, particularly citing the work and teaching of Dr. Richard Wolfson in the following comments.

As most people are aware, Earth's climate would be considerably colder without the naturally occurring greenhouse effect - about 0 degrees Fahrenheit on average instead of the 58 to 60 degree average. The term greenhouse effect is a bit of a misnomer in that a greenhouse blocks heated air whereas the "greenhouse" gasses we discuss here are opaque to infrared radiation from the sun as it attempts to travel back into space off the Earth's surface. Not quite the same thing as what actually happens in a greenhouse.

Nonetheless, the term has stuck, so we have greenhouse gasses creating the greenhouse effect. Water vapor is indeed the dominate atmospheric greenhouse gas for Earth's natural greenhouse effect. Incidentally, this isn't a secret that scientists are trying to keep from the public in order to promote their scare tactics and get grant money. As ludicrous as that statement sounds, I have heard such assertions in "debates" put forth in other forums as an argument denying climate change or CO2 buildup as a real concern.

In any case, even though water vapor is the predominate gas for the naturally occurring greenhouse effect, carbon dioxide plays a more important role in varying the strength of global warming.

The reason for this is due to the almost instantaneous adjustments of water vapor to changing conditions, cycling through the climate system normally in as little as a week. Carbon dioxide, on the other hand, sticks around in the atmosphere for decades. Thus, an increased input of CO2 into the atmosphere does not adjust to current conditions - it doesn't rain liquid CO2. It builds up and thus drives the degree of global warming much more than water vapor.

To sum up, water vapor is indeed the dominate greenhouse gas involved in the naturally occurring greenhouse gas. Due to its quick adjustment to environmental changes in the atmosphere, it helps keep the energy balance of the climate system relatively stable. Carbon dioxide, while much less prevalent than water vapor, lingers in the atmosphere much, much longer (decades) and thus will steadily increase in atmospheric volume, altering the naturally occurring energy balance of the climate system. This is why CO2 has a greater role in determining the strength of the greenhouse effect


climate changeglobal warmingco2carbon dioxidegreenhouse gasgreenhouse effect


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