3. After water vapor, CO2 is the next most important atmospheric trace gas which has both
natural and anthropogenic sources.
a.) What are the dominant natural and anthropogenic sources of CO2?
b.) What is the current level of CO2 in the atmosphere (in ppmV and in % vol)?
c.) What is the average annual rate of the CO2 increase? Also, why does the atmospheric
CO2concentration show a seasonal variability?
Solution
Answer :
3.
(a) There are two primary sources of CO 2 :
(i) Natural CO 2 sources : These sources include animal and plant respiration, decomposition of
organic matter, forest fire and emissions from volcanic eruption.
(ii) Anthropogenic (man-made) CO 2 sources : These sources are those produced from power
generation, transportation, industrial sources, chemical production, petroleum production and
agricultural practices.
(b) Current level of CO 2 in atmosphere = 0.041% by volume of the atmosphere = 410 ppmV
(Source : National Oceanic and Atmospheric Administration)
(c) Annual rate of CO 2 = 3 ppm (Source : National Oceanic and Atmospheric Administration)
Seasonal variability in atmospheric CO 2 concentration : Levels of carbon dioxide in the
atmosphere rise and fall each year as plants, through photosynthesis and respiration, take up the
gas in spring and summer, and release it in fall and winter. The respiration of plants is not evenly
distributed through seasons since the northern and southern hemisphere have a different amount
of land and plants. The southern hemisphere has far less land. In the northern winter, the carbon
released increases and then by May the northern hemisphere has enough carbon uptake (due to

increased photosynthesis) to cause a dip in the CO 2 record. Then summer in the north ends and
autumn commences, and net CO 2 starts to rise again.