Question 9. What Are the Greenhouse Gases? [Quorvita]

A What is a Greenhouse Gas?

Most dictionaries define a greenhouse gas as one that contributes to the “greenhouse effect” by absorbing infrared radiation, such as carbon dioxide from fossil fuels.  However, this type of definition uses bootstrap conditions to define itself.  Greenhouse gases are characterized by their chemical makeup.  One CO2 molecule is the same as another CO2 molecule.  Attempting to measure, detect or analyze which molecules come from which source is physically impossible.  A greenhouse gas is a convenient and useful analogy in describing a gas that absorbs and emits longwave infrared radiation.  It has nothing to do with greenhouses.

B What are the Greenhouse Gases?

There are many gases that absorb and emit infrared radiation.  The most dominant one is water vapor (H2O), at an average concentration of 30,000 ppmv.  The next gas is CO2, at a distant 407 ppmv, and then further down the line is methane, at 1.7 ppmv.  A size comparison would be the Statute of Liberty (H2O), next to a four foot two inch man (CO2), next to a baby mouse (CH4 -methane).  Water vapor makes up 98.3% of all greenhouse gases in the atmosphere.   

C. What Does the Greenhouse Gas Absorption Profiles Mean?

The Greenhouse Gas only absorbs infrared (heat) in accordance with its spectral absorption profile.  Water vapor has the largest profile being able to absorb the most.  Water vapor is the only greenhouse gas possessing some absorption profile within the infrared window.  The two conditions that control the amount of absorption are concentration and absorption profile.  Water vapor dominates both conditions.

D. What is Residence Time?

Residence time has nothing to do with buildings.  It is used to calculate how long a pollutant will last under steady state conditions in a large reservoir.  The argument that a gas with a short residence time means you can ignore it in making projections is without corroborating support.   A pollutant that is constantly replacing itself is still a pollutant.


Water vapor overwhelmingly dominates all other greenhouse gases in the atmosphere by such a large percent that carbon dioxide, methane, and all other gases have a trivial effect.