Why are we not taking into account CO2 emissions through respiratory processes?

Globally, livestock is the most important anthropogenic source of methane emissions (USEPA, 2006a). Methane is a powerful GHG with ~20 times the global warming potential of CO2. In this statistics emission from respiration of human beings is not included. So we are not counting 6.9 billion populations who are continuously emitting CO2. Nature has the answer to this.

Due to human activities, the amount of CO2 released into the atmosphere has been rising extensively during the last 150 years. As a result, it has exceeded the amount sequestered in biomass, the oceans, and other sinks.

There has been a climb in carbon dioxide concentrations in the atmosphere of about 280 ppm in 1850 to 364 ppm in 1998, mainly due to human activities during and after the industrial revolution, which began in 1850.

Humans have been increasing the amount of carbon dioxide in air by burning of fossil fuels, by producing cement and by carrying out land clearing and forest combustion. About 22% of the current atmospheric CO2 concentrations exist due to these human activities, considered that there is no change in natural amounts of carbon dioxide.

Ratio of human beings emitting in atmosphere through respiration is in proportion to plants and trees who convert this CO2 into O2 in the process called photosynthesis.

With the destruction and burning of the rain forests more and more CO2 is being released into the atmosphere. Trees play an important role in producing oxygen from carbon dioxide. "A 115 year old Beech tree exposes about 200,000 leaves with a total surface to 1200 square meters. During the course of one sunny day such a tree inhales 9,400 liters of carbon dioxide to produce 12 kilograms of carbohydrate, thus liberating 9,400 liters of oxygen. Through this mechanism about 45,000 liters of air are regenerated which is sufficient for the respiration of 2 to 3 people". (Breuer 1) This process is called photosynthesis which all plants go though but some yield more and some less oxygen. As long as no more wood is burnt than is reproduced by the forests, no change in atmospheric CO2 concentration will result. Therefore Animals and trees are complimentary to each other.
Carbon dioxide, Lenntex, 2008 http://www.lenntech.com/carbon-dioxide.htm 

This brings us to one conclusion that human population must always be in proportion to environmental resources.