The Carbon Cycle – a brief
introduction
Dr Timothy Lane – [email protected]
Outline
1. Brief introduction to the
carbon cycle
2. Carbon cycle as a system
3. Carbon cycle and humans
4. Atmospheric carbon
5. Oceanic carbon
6. Terrestrial carbon
7. Summary
The Carbon Cycle
• Carbon is the basis for life, we are made of it, eat it,
and civilisation is built on it.
• Carbon is stored in rocks, soil, fossil fuels, plants,
atmosphere, ocean
• The carbon cycle is the flow between these
reservoirs
• Over the long term, the cycle is able to maintain a
balance which prevents all carbon entering the
atmosphere.
• This keeps the Earth’s temperature relatively stable.
The Carbon Cycle
• Carbon is the basis for life, we are made of it, eat it,
and civilisation is built on it.
• Carbon is stored in rocks, soil, fossil fuels, plants,
atmosphere, ocean
• The carbon cycle is the flow between these
reservoirs
• Over the long term, the cycle is able to maintain a
balance which prevents all carbon entering the
atmosphere.
• This keeps the Earth’s temperature relatively stable.
The Carbon Cycle – a system
• Any biogeochemical cycle can be
understood as a system.
• A systems approach is central to
Environmental Science.
• These have inputs, outputs, and
throughputs.
• Throughputs are mediated by processes
within the system. These processes (subsystems) often interact with one another.
The Carbon Cycle – a system
• Key to cycles and systems are:
• Stores
• Fluxes
• Processes
• Systems are often “black boxes”. We
quantify inputs and outputs.
• Only possible to fully understand the
system if we can understand the
subsystem.
The Carbon Cycle and humans
• Humans (since c.1750)
have impacted on the
carbon cycle.
The Carbon Cycle and humans
• Humans (since c.1750)
have impacted on the
carbon cycle.
• Land use change and
depletion of fossil fuels
are the two largest
impacts.
• 90% of anthropogenic
carbon is from
combustion of fossil fuels
The Carbon Cycle
• “Simplified” schematic of the
global carbon cycle.
• Units are petagrams.
1 petagram =
1,000,000,000,000,000 kg
• Black arrows = prior to IR
• Red arrows = ‘anthropogenic’
fluxes
• From IPCC AR5
The Carbon Cycle
• “Simplified” schematic of the
global carbon cycle.
• Units are petagrams.
1 petagram =
1,000,000,000,000,000 kg
• Black arrows = prior to IR
• Red arrows = ‘anthropogenic’
fluxes
• From IPCC AR5
Slow carbon cycle
• Over long timescales (millions to tens of millions of years) tectonic
plate movement charge the rate of carbon seep from the Earths
interior
Slow carbon cycle
• Onset of Himalayan uplift (50 Ma) provided a large source of fresh
rock and carbon could be pulled into the slow carbon cycle
Slow carbon cycle
• A correlation between
CO2 and isotopic (dD)
temperature anomalies
in the Vostok ice core.
• Past 420,000 years
Atmospheric carbon
• Occurs as Greenhous gasses CO2
and CH4
• CH4 is 23 x more powerful than
CO2
• CO2 = 50 year residence time
• CH4 = 12 year residence time
Atmosphere
• Measurement of
from Hawaii
• “Keeling Curve”
• What trends can
you see?
Oceanic carbon
• Oceans store a significant amount of
carbon
• A quarter of human-produced
carbon dioxide emissions get
absorbed into the ocean.
• Held in water (dissolved) and in
oceanic organisms
• Primary input/output through
gaseous exchange with atmosphere
• The greenhouse gas diffuses from
the atmosphere into the ocean
Oceanic carbon
• CO2 rich air meets seawater
containing less
• The greenhouse gas diffuses into
the ocean.
• This warm, CO2-rich surface water
flows to colder parts of the globe,
releasing its heat.
• The now-cool water sinks several
km deep, carrying carbon to deep
water.
Blue = CO2 uptake
by the ocean
Terrestrial carbon
Terrestrial carbon
Predicted changes in soil carbon by 2050 under a 1 °C rise in
global average soil surface temperature.
Total reductions in the global C pool under 1°C and
2°C global average soil surface warming by 2050.
Glacier carbon
Summary
• Carbon cycle is vital for life on Earth
• A natural cycle which we have now perturbed
• Numerous different parts (atmospheric, oceanic,
terrestrial)
• Accelerated (anthropogenic) release of carbon through
various sources leads to atmospheric (and terrestrial)
warming.