ENDY 6013 - ENVIRONMENTAL DYNAMICS

HOMEWORK ASSIGNMENT #5 - IS IT GETTING HARD TO BREATHE IN HERE?

DUE FRIDAY, 27 October 2006

Awareness of the possible environmental effects of massive combustion of fossil fuels increased dramatically during the 1960’s. In 1968, Dr. Paul Erlich declared in his book "The Population Bomb" that wholesale combustion of fossil fuels by human societies would ultimately deplete atmospheric oxygen. Not surprisingly, this hypothesis generated good deal of hand wringing concerning the possible impacts of fossil fuel combustion on the quantity of oxygen in the atmosphere. The arguments surrounding this conjecture followed this line a reasoning:

The oxygen produced in our atmosphere is released by photosynthesis. In the process, organic matter is also produced. Production of oxygen and organic matter is balanced primarily by biological respiration, which consumes oxygen and breaks down organic matter. That is:

Photosynthesis CO2 + H2O CH2O + O2

Respiration CH2O + O2 CO2 + H2O

Thus, the global cycle of oxygen is linked to the global cycle of carbon through photosynthesis and respiration. Combustion of fossil fuel may be viewed as a form of respiration since oxygen is being used to break down organic matter that escaped decay millions of years ago. Therefore, burning fossil fuels on a massive scale may upset the steady state of the present oxygen cycle by creating an imbalance between O2 production and consumption.

In response, renowned geochemist, Dr. Wallace S. Broecker, published an article in the journal Science entitled "Man's Oxygen Reserves" (Broecker, W.S., 1970, Man's oxygen reserves: Science, v.168, p.1537-1538). Obtain a copy of this paper from the library and use it to complete this week's assignment.

Consider the following facts about the global oxygen budget to determine whether or not concern over this matter is warranted:

Data you will need:

Area of the Earth (in m2)

Amount of oxygen per m2

Annual oxygen production by land plants (in moles/m2/y)

Annual oxygen production by ocean plants (in moles/m2/y)

Annual rate of organic carbon preservation (in moles/m2/y)

Total amount of fossil fuel burned by 1970 (in moles)

Know that for every mole of carbon respired, 1 mole of O2 is consumed.

Calculate the following:

  1. The total quantity of oxygen in the atmosphere (in moles).
  2. The total quantity of oxygen produced by all plants each year (in moles).
  3. The total quantity of organic carbon preserved each year (in moles).
  4. The total quantity of oxygen left over from carbon burial each year (in moles).
  5. The total quantity of oxygen consumed by biological respiration each year (in moles).
  6. The total quantity of oxygen used to combust all fossil fuel up to 1970 (4% of recoverable reserves)
  7. Percent of atmospheric oxygen represented by "f" above.
  8. Percent change in atmospheric oxygen if all fossil fuel reserves were depleted.
  9. Assume that all photosynthesis and respiration cease and that fossil fuel reserves are unlimited. If fossil fuels were burned at a rate of 1 x 1014 moles/y, how long would it take to deplete all atmospheric oxygen?
  10. Does there appear to be an impending "oxygen crisis" on Earth as a result of fossil fuel burning?