Māris kļaviņŠ, azamat azizov, JĀnis zaļoksnis environment, pollution, development: the case of uzbekistan

Figure 4.19. 
Changes 
in greenhouse gas 
concentrations and the 
effect of these changes 
on the intensity of 
incoming solar radiation 
for the period of the last 
10 000 years

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66 
ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
form of dissolved carbon dioxide and methane. The atmo sphere 
contains  approximately  760  billion  tons  of  carbon  in  the  form  of 
such compounds as carbon (II) oxide (CO), carbon (IV) oxide (CO
2
) 
and methane (CH
4
).  Carbon  compounds  have  different  cycling 
periods at each stage of the cycle: in the atmo sphere it is quite 
short – 3 years, in the soil – 25 years, in the oceans – 350 years, 
while the cycling period of carbonate rocks is more than hundreds 
of millions of years. 
The living, photosynthetic organisms of the biosphere that conti-
nu ously absorb CO
2
 from the atmo sphere, forming organic com-
pounds, have vital functions in the carbon cycle. CO
2
 goes through 
a complete cycle in the atmo sphere in a relatively short period of 
time – approximately four and a half years.
Not  all  dead  organisms  and  plants  decompose  immediately.  A 
small fraction of them reach the deep parts of inland waterbodies, 
seas and oceans and form sediments there. The organic material that 
decomposes slowly becomes part of the sedimentary rock formation 
process and can return into the atmo sphere in a natural way (for 
example, in the process of erosion).
Carbon dioxide from the atmo sphere can enter waterbodies and 
dissolve there. In water, algae absorb carbon dioxide in much the 
same way as terrestrial plants do. In addition, some aquatic life forms 
extract calcium and carbon dioxide from water to build calcium 
carbonate  shells.  When  these  organisms  die  off,  their  shells  are 
deposited on the bottom of waterbodies, forming limestone. In this 
way, part of carbon becomes involved in the sedimentary rock cycle, 
which will possibly bring it as limestone up to the Earth’s surface 
again in the future. After that, the erosion process and weathering 
will decompose this limestone, and dissolved it will return into the 
ocean, and then, from the ocean, carbon will be released back into 
the  atmo sphere. 
The increase in carbon dioxide and methane emissions can 
become  a  factor  that  will  adversely  affect  the  environ mental 
processes and carbon cycle. Estimates show that the amount of 
anthropogenic emissions of CO
2
 have been increasing on average for 
2.5% per year within the last hundred years (Figure 4.19). Shrinking 
of forest areas also affects the concentration of CO
2
 in the air. The 
current amount of CO
2
 anthropogenic emissions is 9.0 × 0.5 GtC per 
year; however, depending on the World’s population growth scenario, 
it is estimated that these emissions can increase up to 35.8 GtC per 
year by 2100.
Human economic activity changes the carbon cycle and 
enhances the release of the carbon compounds accumulated in 
the litho sphere into the atmo sphere. Fossil fuel combustion and 
deforestation make CO
2
 pass from the litho sphere and biosphere 

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4. HUMANS AND THE ENVIRONMENT
 67
into the atmo sphere much faster than it would occur in a natural 
way. At the same time, the return of CO
2
 from the atmo sphere in a 
natural way takes place much slower than when it is aided by human 
economic activity. In effect, the amount of CO
2
 in the atmo sphere 
irreversibly increases.
Methane plays a substantial role in the carbon cycle. Methane 
absorbs infrared radiation more effectively than CO
2
; therefore, its 
increase boosts the greenhouse effect, even if methane’s concentra-
tion in the atmo sphere is lower than that of CO
2
. Since the 60s of 
the last century, when the atmo spheric methane concentration 
measurements began, its total concentration has increased for an 
average of 1% per year. Part of methane is generated as a result 
of rice and livestock farming, especially from cattle. Historically 
methane concentration changes, like those of CO
2
, have been related 
to the climate changes during the ice ages and interglacial periods. 
However, in recent years research shows that geological processes 
can  also  be  a  significant  source  of  methane.  For  example,  such 
natural phenomenon as mud volcanoes is deemed to originate almost 
10% of the atmo spheric methane.
2
4
6
8
10
0
1700
1750
1800
1850
1900
1950
2000
Years
CO
2
 emissions (GtC/year)
The concentration of carbon dioxide in the atmo sphere has 
increased from 280 parts per million in the pre-industrial period to 
385 parts per million in 2008 (Figure 4.20). Probing the composition 
of the air trapped in the continental glaciers has proved that the 
concentration of CO
2
 today is significantly higher than it had been 
during the last 650 000 years (180-300 ppm). Human activity is the 
main factor contributing to the increase of CO
2
 concentration in the 
atmo sphere and affecting the whole carbon cycle.