I have read a great deal about the Mauna Loa measurements of atmospheric CO2 concentration, as well as those made at other sites. My query relates to how the CO2 is assumed to be distributed globally when calculating either total accretion in the atmosphere or its effects on climate and temperature.
My personal observation of the effect of water vapor (humidity) is based on having grown up in the exceptionally dry Sonoran Desert of the Great Basin, while spending my adult life in the Texas Gulf Coast climate. I would have to assume that CO2 is at least as variable in concentration around the globe as is water vapor, and that it is therefore equally likely to be exceptionally regional in its effects. I would be very interested in any citations you may have to journal articles on this subject.
Submitted by: John Black, Houston, TX
Answer:
Actually, your assumption about atmospheric CO2 concentration being at least as variable as water vapor (humidity) is incorrect. Although the air's CO2 content does vary through the year with the seasonal growth and decay of terrestrial vegetation [see Carbon Dioxide (Seasonal Atmospheric Cycle) in our Subject Index], and although it also varies diurnally with the daily cycle of vegetative photosynthesis and respiration, as well as spatially across transitions between rural and urban areas [see Carbon Dioxide (Urban CO2 Dome) in our Subject Index], it does not vary nearly as much as water vapor varies from time to time and from place to place.
In the Sonoran Desert environment of Phoenix, Arizona, for example, the water vapor pressure of the air can rise three-fold almost overnight with the advent of the summer monsoon (Hales, 1974; Idso, 1982); and Idso (1981) has measured vapor pressures there that range from 3 to 30 mb, spanning a full order of magnitude in variability. Nowhere on earth will you find such variability in atmospheric CO2 concentration, except in the vacinity of natural CO2 vents and "soda springs," such as are described in our Book Review Plant Responses to Elevated CO2: Evidence from Natural Springs. Compared to water vapor, CO2 is a well-mixed component of the atmosphere.
References
Hales, J.E., Jr. 1974. Southwestern United States summer monsoon source -- Gulf of Mexico or Pacific Ocean? Journal of Applied Meteorology 13: 331-342.
Idso, S.B. 1981. A set of equations for full spectrum and 8- to 14-µm thermal radiation from cloudless skies. Water Resources Research 17: 295-304.
Idso, S.B. 1982. A surface air temperature response function for earth's atmosphere. Boundary Layer Meteorology 22: 227-232.