by Jeffrey Graf

Created on: March 01, 2010

The term footprint has come to mean the balance of carbon dioxide (CO2) taken out of the atmosphere and carbon dioxide put into the atmosphere.  CO2 is removed from the atmosphere primarily by photosynthesis and enters the atmosphere again either through respiration or combustion. It is believed that CO2 plays a direct role in the thermal balance in the atmosphere, but we should not overlook the effect of water vapor on the atmosphere, as it is also a product of respiration, and transpiration which usually occurs in conjunction with photosynthesis in terrestrial biomes.

  The data that is most references, and has been a standard touchstone in oceanographic and atmospheric textbooks comes from a National Oceanographic and Atmospheric Administration (NOAA)  run field station in Mauna Loa, Hawaii. Hawaii has been chosen as a field station for observation of global trends in the atmosphere because it is so far away from large scale local perturbations to the atmosphere by human activity. In other words, it is presumed that the atmosphere has been well mixed by the time it reaches an observation point in Hawaii, and so only global trends are observed. NOAA keeps recent data online here, and you should look at it to follow the rest of the discussion. The site is also listed in reference [1] .

There are two things that we immediately recognize from the month by month plot of CO2 at Mauna Loa, here after called the Mauna Loa plot. First is that the amount of CO2 in the atmosphere is continually increasing, as emphasized by the slope of the plot of average values. The second thing that we notice is that there is a yearly cycle to be observed in the data.  It is from the yearly cycle observed in the data that we can make inferences about the impact of different hemispheres on photosynthesis, and as a result, the CO2 balance in the atmosphere.

The time axis is broken down into quarters, and what we notice is that CO2 concentration reaches a maximum at the end of the first quarter, which corresponds to the end of winter in the northern hemisphere, and as such, the beginning of the spring bloom, or return of primary production, as the spring turns into summer, we see the negative slope of the CO2 concentration reaches a maximum at about the end of the second quarter, or the early summer peak in photo synthesis in the northern hemisphere.

 Obviously then the reverse process begins, in the fall as the northern hemisphere cools and photosyntesis

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