Geoscience Reference
In-Depth Information
gases. Greenhouse gases, other than CO
2
, can in the future play an unpredictable
role in formation of the Earth radiation balance. Therefore some models are pro-
posed here which enable one to parameterize part of the indicated elements.
1.6 Block Schemes of Models for Biogeochemical Cycles
1.6.1 Schemes of the Global Carbon Cycle
The reliability of the assessment of the role of CO
2
in the greenhouse effect for-
mation depends on a detailed consideration of the global biogeochemical carbon
cycle dynamics in the models and on the accuracy of the assessment of its char-
acteristics. There are dozens of diagrams of the global carbon cycle in the form of
CO
2
changes. Consider some of them to demonstrate their principal features and to
understand the limit for necessary details of the simulation of the carbon cycle
compounds, beyond which it is impossible to obtain an additional knowledge about
this cycle and, hence, about the greenhouse effect due to CO
2
. Note that all known
diagrams of the global CO
2
cycle are divided into two classes: point wise (globally
averaged) and spatial (locally averaged). All the diagrams are similar in that the
biosphere is divided into the atmosphere, oceans, and land ecosystems. Many
diagrams divide carbon into organic and inorganic forms. As a rule, the time step of
averaging all processes and reservoirs of carbon is assumed to be 1 year, and
therefore the atmospheric reservoir is considered as homogeneously mixed-up
(pointwise). The World Ocean and surface ecosystems are considerably detailed.
This detailing is based on global data bases for these reservoirs of carbon. As a rule,
the
final results of the diagrams studies are either of methodical character or they
predict the atmospheric CO
2
concentrations within the limits of a certain scenario of
the anthropogenic activity.
The schemes in Figs.
1.23
and
1.24
give an idea about the amounts of carbon
supplies for its basic reservoirs. The estimates shown in this scheme differ drasti-
cally from the estimates by other authors. Nevertheless, their relationships and
orders of magnitude coincide in most cases. As seen, the largest carbon supply is
concentrated in the World Ocean. A minimum of it is in the atmosphere.
Natural processes determining the global carbon cycle dynamics have various
time scales. Some of them, such as burying the dead organic matter at the bottom of
the oceans, have characteristic time scales of hundreds and thousands years. Others,
for instance the biological carbon cycle on land, have a period of several tens of
years. Therefore a consideration of the timescales of the carbon cycle in the bio-
sphere is an important stage of studies of the dynamics of the CO
2
content in the
atmosphere. Here it is also important to consider the fact that the characteristic time
of the complete mixing of the atmosphere constitutes from several months to
2 years. Regular measurements at different stations of monitoring have shown that
the CO
2
concentration varies considerably during 1 year. The difference between
maximum and minimum estimates of the atmospheric CO
2
concentrations varies
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