THE CARBON CYCLE: THE FACTS
Carbon is essential to all life. However, the burning of fossil
fuels and the consequent build-up of carbon dioxide in the
atmosphere has led to severe concerns regarding climate
change. Here, International Innovation takes a look at the
movement of this essential element through the Earth’s system
The carbon cycle can be separated into two
different, but interacting domains:
The fast domain – is considered the most
important when considering anthropogenic
climate change. It is made up of large
exchange fluxes and relatively rapid
carbon store turnovers. Turnover times of the
reservoirs within the fast domain range from
a few years to millennia.
The slow domain – consists of huge carbon
stores in rocks and sediments, which exchange
OCEAN
The ocean is the largest carbon reservoir
in the fast domain, holding around:
38,000 PgC
as dissolved inorganic carbon (DIC)
700 PgC
as dissolved organic carbon (DOC)
~ 3 PgC
as marine biota
-1
0.9
PgC
y
r
A total of
is transferred from rivers to oceans
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INTERNATIONAL INNOVATION
carbon with the fast domain through volcanic
eruptions, chemical weathering and erosion.
Turnover times of the reservoirs in this domain
span 10,000 years or longer.
The natural exchange between the two domains
is relatively small (<0.3 PgC yr-1). However,
fossil fuel extraction from geological reservoirs,
and subsequent combustion has caused an
unparalleled transfer of fossil carbon from the
slow to the fast domain, causing a significant
human-induced perturbation in the natural
carbon cycle.
ATMOSPHERE
Carbon is stored in the atmosphere
as CO2
Total current store of CO2 in
the atmosphere:
828 PgC
Ocean-atmosphere gas exchange:
78.4 PgC y r -1
Atmosphere-ocean gas exchange:
80 PgC y r -1
Net flux to the ocean:
1.6 PgC y r -1
THE CARBON CYCLE: THE FACTS
TERRESTRIAL BIOSPHERE
Carbon in the terrestrial biosphere has multiple stores:
450-650 PgC
dead organic matter/soils: 1500-2400 PgC
wetland soils: 300-700 PgC
permafrost soils: 1700 PgC
living biomass: ~
Plant photosynthesis removes CO2 from the atmosphere
-1
at a rate of
±
123 8 PgC y r
Respiration processes release
back into the atmosphere
118.7 PgC y r -1
4.3 PgC y r -1
Net flux to the biosphere:
ANTHROPOGENIC EMISSIONS
OF CARBON
Net Flux of carbon to the atmosphere:
7.8 ± 0.6 PgC y r -1
-1
Net land use change: 1.1 ± 0.8 PgC y r
Fossil fuels:
LITHOSPHERE
66-100,000,000 PgC
The lithosphere contains
as marine sediments and sedimentary rock
Fossil fuels store carbon as:
gas: 383-1135 PgC
oil: 173-264 PgC
coal: 446-541 PgC
Lithosphere to atmosphere flux:
0.1 PgC y r -1
PgC yr-1 = Pentagrams of carbon per year
1 PgC = 1015 g carbon = 1 billion metric tonnes carbon
Source:
Intergovernmental Panel on Climate Change (IPCC)
2013 report, Climate Change 2013: The Physical
Science Basis. Contribution of Working Group I to
the Fifth Assessment Report of the Intergovernmental
Panel on Climate Change, ed T F Stocker, D Qin,
G K Plattner, M Tignor, S K Allen, J Boschung, A
Nauels, Y Xia, V Bex and P M Midgley, Cambridge
University Press, Cambridge, UK, and New York,
NY, USA
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