The Carbon Cycle


The carbon cycle:

a biogeochemical cycle where carbon is stored and moved between spheres through flows/fluxes. 

It is a closed system

Stores ADD carbon to the atmosphere 

Sinks REMOVE carbon 

Flux: movement of organic compound through an ecosystem 

The carbon cycle must be balanced to support planetary health 

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Terrestrial Carbon Stores

Geological has the slowest turnover rate, carbon enters and leaves very slowly. 

It is stored in rocks and sediment and leaves through volcanic emissions or weathering 

Biological cycle has a faster turnover, carbon is not sequestered for long, between the oceans, atmosphere and vegetation 

Sequestering: the natural storage of carbon by physical or biological processes (e.g. Photosynthesis)

Stores of Carbon: 

Limestone & Shale 

Fossil Fuels 



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Formation of Fossil Fuels

Oil & Natural Gas: 

-formed from remains of aquatic animals & plants 

-gas & oil occur in pockets in rocks


-formed from remains of trees, ferns & other plants 

-4 main types of coal; Anthracite, Bituminous, Lignite & Peat

Volcanic Outgassing: 

-pockets of CO2 escaping from the earth's crust from volcanic activity or earthquakes 

-outgassing occurs at; active/passive volcanoes with tectonic plate boundaries 

-plates with no current volcanic activity e.g. hot springs or geysers 

-emissions from fractures in the earth's crust 

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Carbon Pumps

Biological pump: organic sequestration of CO2 to oceans by Phytoplankton

-carbon passed up the food chain by fish & zooplankton which release CO2 into the water & atmosphere 

Carbonate pump: inorganic carbon sedimentation

-marine life use Calcium Carbonate to form shells & skeletons e.g. corals, oysters etc.

-when organisms die & sink, shells dissolve and carbon is released

Physical Pump: oceanic circulation of water upwelling/downwelling & thermohaline current 

-the colder the water, the more CO2

-warm waters release more, cold take in more 

Thermohaline circulation: global system of surface & deep water ocean currents driven by temperature & salinity differences between areas of the ocean

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Biological processes

Biological processes sequester organic carbon on land- quickest part of the cycle 

1. primary producers (plants) remove carbon through photosynthesis & release through respiration

2. consumers (insects) eat plants, carbon becomes part of their fat/protein 

3. Microorganisms (beetles) feed on waste material from animals & gain carbon 

4. storage of carbon is mainly in plants/soils, the largest in trees, the least in animals 

Terrestrial Carbon Stores 

Amazon Rainforest; absorb more than they release, regulate global carbon levels 

Mangroves; most carbon rich species on the planet, double those of forests  

Tundra Soils; natural carbon stores, form at high latitudes in cold temperatures 

Arctic Permafrost; stores carbon, released as they melt 

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A balanced carbon cycle

The Greenhouse effect: 

- heat energy comes from the sun through SHORT WAVE radiation 

-it has a lot of energy to pass through the atmosphere 

-on reaching the earth's surface, it is either absorbed or reflected (albedo)

-at night, earth's surface cools & heat energy is released in LONG WAVE radiation 

-this has less energy to escape & is absorbed by Greenhouse gas molecules 

This sustains warm temperatures on earth, allowing humans to survive 

Changing levels of CO2 over time: 

-levels of carbon naturally fluctuate due to volcanic outgassing, solar flares & amounts of vegetation 

-carbon levels have increased more rapidly recently due to burning fossil fuels 

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Impacts of burning fossil fuels

Fossil fuel combustion releases carbon into the atmosphere 

-combustion has altered the carbon balance, flows have greatly increased 

-rising levels of CO2 have lead to an increase in temperature 

-annual precipitation will increase 

-extreme weather events are more likely 

Arctic: warming 2X as fast as global average 

melting permafrost releases CO2, sea ice melts, habitats lost 

Hydrological cycle: 

change in rainfall patterns

more floods in winter, more droughts in summer 

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Energy Security

Energy security: the uninterrupted availability of energy sources at an affordable price 

4 aspects of energy security: 

-availability              -accessibility             -affordability              -reliability 

Energy intensity: a measure of how efficiently a country uses energy

HIGH intensity means high price of converting energy into GDP

energy intensity DECREASES with economic development

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Factors affecting the consumption of energy

environmental priorities

-renewable energy is expensive

physical availability 

-energy has to be imported if not available, consumer cost increased, air miles 


-colder climates require more energy e.g. heating, low consumption in Africa 

economic development 

-richer countries can afford more energy, opposite for poorer; prices are relative to economy 


-delivery to consumer, processing (primary to secondary), physical exploitation 

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Energy Players

Main worldwide energy players: 

-TNCs, OPEC, Governments, Energy companies & consumers/pressure groups 

Consumers; highly price sensitive, can exert pressure on politicians 

Energy TNCs; exploration for reserves, exploitation & refining

Scientists, R&D; research into alternatives fuels

OPEC; key role in global prices, manage production 

Environmentalists; pressure to adopt renewables & reduce carbon intensity  

Generators & distributors; national grid & power stations (infrastructure)

Governments; National energy mix, subsidies and grants 

Energy mix: combination of different available energy sources used to meet a country's demand

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Energy pathways - Mismatch between supply & demand

Energy pathways: the flow of energy from producer to consumer

-e.g. by pipelines, shipping, rail, road or transmission lines 

What makes a good energy pathway?

-good relationships between countries

-pipelines will try to avoid using transit states to transport the energy

Transit state: country/state through which energy flows from producer to consumer 

How pathways can be disrupted: 

Disturbance at chokepoints- can be blocked, disrupted; causes prices to rise 

Geopolitical conflict - fight to gain control over resources 

Piracy- oil stolen by pirates  

Natural Hazards - extreme weather can damage pipelines 

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Unconventional fossil fuels

unconventional fuels: deep water oil, oil shale, tar sands & shale gas 

Recyclable and renewable energy: helps to reduce carbon levels

examples include: Wind turbines, Solar power, Hyrdo electric, nuclear energy & biomass

Nuclear energy is not a renewable energy source as it needs uranium (a finite resource)

deep water oil - found at considerable depths in the ocean 

tar sands - a mixture of sand, water, clay & bitumen 

shale gas - natural gas trapped in sedimentary rocks 

oil shale - oil bearing rocks that are permeable enough to allow oil to be pumped out directly 

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Reliance on fossil fuels

renewable energy - capable of natural regeneration & provides continual flow of energy

e.g. water, wind, tidal, waves, geothermal & solar 

recyclable energy - can be renewed but only as a result of human intervention

e.g. harnessing nuclear power or biofuel

Primary biofuels - organic matter (fuelwood, wood chips) used in unprocessed form for cooling, heating & electricity

Secondary biofuels - derived from processed biomass & include liquid biofuels such as ethanol and biodiesel 


Radical alternatives to reduce carbon emissions: Carbon capture and storage, hydrogen fuel cells, electric vehicles & solar cooking 

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Carbon & water cycles link to global climate

Growing demand for resources e.g. food, fuel & water has led to land conversion 

land conversion: change from natural ecosystems to an alternative use; usually reduces carbon & water stores as well as soil health 

countries with highest rates of deforestation: 

Nigeria           Indonesia           North Korea          Bolivia          Papua New Guinea

Impacts of deforestation: 

Water cycle - runoff increased, higher flood peaks, annual rainfall reduced (droughts)

Soil health - rapid soil erosion, minerals lost, biodiversity decreased 

Atmosphere - reduced evapotranspiration, reduced shading (forest floor)

Biosphere - species diversity reduced, decrease in habitat

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Impacts of human activity

Kuznet's environmental curve: hypothesised relationship between environmental quality & economic development

-as modern economic growth occurs, environmental degredation gets worse 

afforestation - establishing new forests where there were no trees before 

reforestation - replanting trees where they were previously 

ecosystem reliance - the level of disturbance that ecosystem can cope with while keeping their original state 

critical threshold - a point beyond where damage becoms irreversible 

ocean acidification - when CO2 in the ocean increases, the ocean pH decreases- the ocean becomes more acidic 

coral bleaching: when water becomes too warm, algae is effected & coral turns white

CORALS: shelter marine species, protect shorelines, support fishing, income for tourism  

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implications for human wellbeing from degradation

forests & human wellbeing:

Human wellbeing: everyone aspires to live well worldwide, regardless of age, culture, religion or political environment 

provisioning services - food, water, wood, fuel

supporting services - soil formation, habitat production

regulating services - climate & flood regulation

cultural services - spiritual, aesthetic, educational 

current biggest threat to forests is deforestation

factors affecting time of change: 

-wealth                      -law enforcement               -aid           -influence of TNCs

-Education and knowledge 

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Kuznet's curve

3 stages : Pre industrial, Industrial & post industrial 

stage 1 - rapid economic development occurs when demand for products has environmental impacts 

stage 2 - concern at degredation leads to action to protect environment 

stage 3 - reinforcement of stage 2 occurs with education & funding for environmental protection 

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impacts of rising temperatures on the water cycle: 

-increased evaporation due to rising temperatures - increased drought 

-more rainfall than snowfall 

-earlier peaks in snowmelt, river flows effected - reduced availability of fresh water in summer 

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Risks of further planetary warning

changes to the Arctic - ocean currents, air circulation & sea level rise - flooding 

GHG - gases are still added faster than carbon stores can take them in, they lead to further planetary warming & remain in the atmosphere for some time 

factors influencing climate change rates - 

population growth - growing demand for resources, causes strain on the environment 

forests (deforestation) - less natural carbon sinks, increased carbon into the atmosphere 

Sea level rise - ocean acidification & loss of biodiversity, also coastal flooding 

economic change - as world economy grows, so does demand for resources, however wealthy countries often put measure in place to stop exploitation 

technology - e.g. turbines and solar power help to diminish negative effects 

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continued . .

feedback mechanisms & tipping points - 

peatlands - huge carbon sinks, cover 3% of global land surface, store soil for millenia  

permafrost - GHG that have been stored in the ice for millenia is relased as the frost melts due to rise in temperatures 

forest die back - caused by global warming & drought; many trees are lost as a result of this and therefore carbon sinks are lost 

changes to thermohaline circulation - melting ice, increases amount of freshwater in the oceans, changes the salinity & could effect flows which could cause drastic temperature change in parts of Europe 

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How can people respond to climate change?

adaptation strategies: adopting new ways to live with the effects of climate change e.g.

solar radiation, resilient agricultural systems, water conservation & land use planning 

mitigation strategies: re-balancing the carbon cycle and reducing any impacts of climate change e.g.

carbon capture storage, renewable switching, afforestation/reforestation, carbon taxation & energy efficiency 

Kyoto Protocol - 2005, 192 member countries

-state parties must reduce GHG emissions - successful as emissions were reduced by 125%

Paris agreement - 2015, 175 member nations 

-dealing with GHG emissions through adaptation, mitigation & finance; starts 2020

success as has bought many nations together HOWEVER the US may pull out 

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Adaptation strategies

water conservation & management - e.g. smart irrigation, reducing agricultural consumption 

helps to conserve water, which is running out 

expensive & challenging 

resilient agricultural systems - growing crops without ploughing & fewer fertilisers 

conserves water, controls erosion,

could decrease yields

land use planning & flood risk management - development of flood plains 

low cost and effective 

land may be needed for alternative things e.g. property 


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adaptation strategies cont.

energy efficiency - residential buildings to reduce energy consumption

helps to reform old builidings & makes them more efficient 

some may be against the renovation 

afforestation & reforestation - forest rehabilitation 

prevents soil erosion & provision of carbon sinks & stores 

often trees planted grow quickly but are not actually that effective at storing carbon 

renewable switching - switching from fossil fuels to renewable energy 

lowers carbon emissions effectively 

can be expensive, some countries cannot afford this option 


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