Anthropogenic Influences on the Global Carbon Cycle and its Implications for the Future
Pushkaraj Sardesai and Sarah Eggleston
Earth System Science and Policy
Abstract
Carbon makes up approximately 50% of the dry weight of all living things; it forms the structure of all life on Earth. While not one of the major atmospheric gasses, carbon compounds such as carbon dioxide (CO 2) and
methane (CH4) are major greenhouse gases, and as such are major contributors to global warming. Currently atmospheric CO 2 concentrations are increasing at a rate of about 3.2 Pg C per year. Based on ice core data and
ongoing atmospheric CO2 monitoring, anthropogenic sources, specifically combustion of fossil fuels and land use changes, have been cited for causing this increase. Here we give a brief overview of how the natural carbon
cycle works and look at how fossil fuel combustion and land use changes affect this cycle over time. We focus on the modifications that have been, and could be made to land use, as well as the potential for carbon
sequestration as a mitigation for atmospheric carbon build up.
Human Impacts On The Carbon Cycle
Carbon Storage Potential of Biomes
Fossil fuel combustion and land use changes, are the main ways in which
humans affect the natural carbon cycle. The natural carbon system cannot
keep pace with these new anthropogenic emission sources. The natural
processes that permanently remove this additional carbon (i.e. ocean uptake
and sedimentation) work extremely slowly so, the concentration of CO2 in
the atmosphere increases.
As can be seen in the graphs to the left, carbon
storage capacity varies by biome. Currently the
Boreal Forest biome stores the most carbon,
followed by Tropical Forests.
Total Global Carbon Stored ( Pg/C) by Biome
600
Carbon Stored (Pg C)
500
400
300
200
100
0
Tropical
Forests
Temperate
Forests
Boreal
Forests
Tropical
Temperate Deserts and
Savannas & Grasslands & Semi-Deserts
Grasslands
Shrublands
Tundra
Croplands
Wetlands
Biome
Total Global Carbon Stocks (Pg/C)
Total Carbon Stored (Pg C) / % Total Land Area Covered
Carbon Stored ( in Pg C) / % Land Area
120
100
80
60
40
20
0
Tropical
Forests
Temperate
Forests
Boreal
Forests
Tropical
Temperate Deserts and
Savannas & Grasslands
SemiGrasslands & Shrublands
Deserts
Biome
Total (Pg C) / % Total Area
Tundra
Croplands
Wetlands
In terms of total carbon per unit area, Wetlands
are by far the most efficient at carbon storage
with Boreal Forests next in efficiency.
For carbon sequestration purposes, the amount
of carbon that can be stored by a biome is quite
important. The location of these biomes is also
important, since the majority of carbon is emitted
in the Northern Hemisphere. The location of
biomes such as the Boreal Forest with their ability
to store large amounts of carbon can make a
great difference for atmospheric carbon
concentrations.
Fossil Fuel CO2 emission and carbon sequestration
CO2 emissions from combustion of fossil fuels is of concern because combustion
adds the long dormant stock of C from Earth’s crust in to the active carbon cycle.
This increased CO2 concentration in atmosphere is a major factor in global
warming.
www.pewclimate.org/ images/figure4.gif
Effect of CO2 & Greenhouse gases
rst.gsfc.nasa.gov/ Sect16/Sect16_4.html
The potential ways to reduce the CO2 concentration in atmosphere are 1) Carbon
sequestration 2) Replace fossil fuels with bio-fuels 3) Reduce the CO2 release
from energy use (by switching to alternative sources of energy)
Natural Carbon Cycle
The Earth maintains a natural carbon balance. Carbon is continually exchanged within a
closed system consisting of the atmosphere, oceans, biosphere, and landmasses. When,
natural perturbations in concentrations of carbon dioxide (CO2) occur, the system gradually
returns to its natural state through the processes shown here. These process can be either
long term or short term.
Biomes
OCEAN UPTAKE Dissolving of CO2
gas into the oceans and inflow of
carbon carried from land by rivers.
OCEAN RELEASE Return of
carbon in the oceans directly back to
the atmosphere as CO2 gas.
SEDIMENTATION Slow burial of
plant and animal matter on land and
on the ocean floor, which eventually
becomes limestone, coal, gas, and
oil.
RESPIRATION Slow combustion of
carbon compounds, producing
energy within organisms and
releasing CO2.
PHOTOSYNTHESIS Conversion of
CO2 into energy-rich carbon
compounds by plants.
Tundra
Boreal Forest
Grasslands
Temperate Forest
Chaparral
Desert
Savanna
Tropical
Forest
Alpine
http://www.blueplanetbiomes.org/world_biomes.htm
Humans change the way land is used in many ways. The most significant of
these ways is through deforestation, desertification, conversion of land to
cropland, and wetland destruction.
The map above shows the basic location and extent of major Earth biomes.
What biomes are changed is of significant importance to the carbon cycle,
as each biome has a different potential for carbon storage.
www.clarkson.edu/.../ Fig8_small.jpe
Possible way to mitigate Point
Source Carbon dioxide Pollution
With help of atmospheric modeling and satellite images, determine the effective radius from
a point source within which the concentration of CO2 are high.
With help of satellite images identify the type and concentration of biomass in the area.
www.koshland-science-museum.org/exhibitgcc/images/carbon02.jsp.
References
1) Janzen, H.H. “Carbon cycling in earth systems – a soil science perspective.” Agriculture, Ecosystems & Environment 104 (2004)
399-417.
2) Jorge L. Sarmiento & Steven C. Wofsy Co-Chairs A U.S Carbon Cycle Science Plan. A report of the Carbon and Climate working
Group. 1999
3) http://www.cypenv.org/Files/sequest.htm
4) http://cdiac.esd.ornl.gov/trends/emis/em_cont.htm
Determine the uptake of carbon dioxide by this biomass. (carbon sequestered).
Determine the potential for carbon sequestration with help of local man managed
ecosystems.
e.g. Trees planted in this radius will sequester carbon more effectively and rapidly then
elsewhere, and reduce overall national emissions.