Environmental Engineering Reference
In-Depth Information
Atmospheric CO
2
Silicate
weathering
Photosynthesis
Biological
activity
Organic
carbon
Biogenic CO
3
=
CO
3
=
Burial
Deposition
Burial
Organic carbon in
sediments
CO
3
=
in sediments
Subduction
Carbon in mantle
Figure 2.2
Long-term carbon cycle.
Table 2.1
Global carbon dioxide budget in gigatons per year for the period 1990 to 1999 and 2000 to 2008.
Period
Fossil-fuel use and
cement production
Land-use
change
Land sink
Ocean sink
Net accumulation
in the atmosphere
1990-2000
6.4
±
0.4
1.6
±
0.7
2.6
±
0.9
2.2
±
0.4
3.1
±
0.1
2000-2008
7.7
±
0.5
1.4
±
0.7
2.7
±
1.0
2.3
±
0.5
4.1
±
0.1
From Canadell et al., 2009.
long-term carbon cycle. Large-scale deforestation releases carbon stored in living plants and
soils and prevents future capture of carbon at global scale (Bala et al., 2007).
The alteration of the carbon cycle has changed the planet carbon budget, resulting in a net
accumulation of carbon dioxide in the atmosphere (Table 2.1). Since measurements were
started in 1958 at Mauna Loa Observatory in Hawaii, a clear growing trend of atmospheric
carbon dioxide is apparent (see Fig. 8.2). In this particular station, the level of carbon dioxide
has raised from 317 ppm in 1958 to 392 ppm in 2010. Carbon dioxide levels vary around the
world, so these values are not representative of global concentrations. However, this is the
oldest set of data that has been obtained by continual direct monitoring for more than fifty
years and shows a definite upward trend.
The hydrologic cycle
The hydrologic cycle, or water cycle, describes the continuous movement of water in the
hydrosphere from the land and oceans to the atmosphere and back again. The process has five
components (evaporation, condensation, precipitation, infiltration, and runoff) and is totally
powered by the sun.
