Biomedical Engineering Reference
In-Depth Information
Atmospheric net carbon Increase 3-4 Gt / y
Fossil Fuels
Release: 6
Net Terrestrial
Uptake: 0-1
Net Ocean
Uptake: 2
Photosynthesis
Photosynthesis
Plant Biomass
Respiration
Microbial
Decomposition
Soil
Deep ocean
Rocks
Sediments
Fig. 2.1.
Simplified global carbon cycle. Biogeothermal carbon cycle is schematized,
distinguishing between terrestrial and aquatic processes. Photosynthesis, which fixes
atmospheric CO
2
is indicated in
black
, while processes responsible of carbon dioxide
release (respiration, microbial decomposition, and fossil fuels combustion) are indi-
cated in
italic
. The net uptake activity of terrestrial and ocean activities are
circled
.
Plants biomass, soil, rock, deep ocean, and marine sediments are indicated in
white
and are sites of long-term carbon storage.
This temperature increase has two major consequences. The first is deser-
tification of subtropical areas, which caused a massive reduction of forests. As
trees are photosynthetic organisms, which fix the atmospheric carbon dioxide
into biomass, their massive reduction is causing further enhancement of car-
bon dioxide accumulation. Although a transitory effect, even more important
is that desertification implies oxidation to CO
2
of the organic mass contained
in the soil (1-2%). The second effect consists into the thawing out of the polar
areas. In these regions, a large amount of CO
2
has been fixed as frozen organic
matter in the underground during several million years. Because of the global
warming, this organic matter is being thawed out and mineralized by bacteria
and fungi causing a further CO
2
evolution.
The public conscience that the search of energy sources alternative to fossil
fuels is fundamental for future prospects is generally increasing, and research
efforts are devoted to this field in several countries. The attention is focused
on renewable resources, such as sun and wind, which can be considered as no
exhaustible. Furthermore, their massive exploitation will drastically reduce
chemical, radioactive, and thermal pollution, and they therefore stand out as
a viable source of clean and limitless energy.
