The Carbon Cycle

  • Created by: barry
  • Created on: 21-05-18 20:18

Changes in the carbon cycle natural causes

Natural climate change

During the quaternary period the global climate fluctuated frequently between inter glacial and glacial periods. With the trend being higher temperatures are associated with high levels of carbon dioxide. So, with an increase level of carbon dioxide in the atmosphere consequently leads to enhanced global warming and subsequent temperature increase. And with lower levels of C02 reduce the effectiveness of the greenhouse effect which leads to global cooling. Therefore, carbon dioxide trigger temperature change, however temperature change can have a impact on levels of carbon dioxide.

Cold conditions- chemical weathering would be more active as cold water can hold more carbon dioxide. Decomposers will have less effective so carbon transfer to the soil will have been less effective. Less water would have followed as it was locked up as snow/ice on the land, so carbon transfer to soil would have been reduced.

Warm conditions- in recent years global temperatures have risen. Consequently, this melts the permafrost in tundra regions (Siberia). Carbon, methane store within permafrost is now being released into the atmosphere where leading to the enhanced the greenhouse effect.

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Changes in the carbon cycle natural causes 2

Wild fires

Can be started naturally by lightning strikes. However, it can be started deliberately by people. It can have regional impacts as these fires release large amounts of C02 into the atmosphere causing notable trend in carbon emissions. This increases the transfer of carbon from the biosphere to the atmosphere.

Volcanic activity

This returns carbon dioxide that has been trapped in the earths crust.  Emitts 100-400 million tonnes of carbon compareed to the 30 billion tonnes released by humans. This increases the transfer of carbon from the lthosphere to the atmosphere

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Changes in the carbon cycle human causes

Land use change:

This is responsible for 10% of carbon released globally, which impacts our short-term store and global warming.

Farming practises- ploughing and harvesting livestock using machinery and fertilisers fuel by FF all release carbon. Cattle farming produces methane as a by-product which is potent greenhouse gas. Methane is produced from the cultivation of rice, with rice primary food source for 50% of the world it has caused an increase in methane emissions.

Urbanisation- replacing open countryside with impermeable surfaces (concrete and tarmac). Impacts local carbon store as stores are either replaced or removed. Also, carbon dioxide is emitted during the production of cement by FF combustion. 

Deforestation- trees are removed either burning or felling. It is widespread across the world but concentrated tropical regions. Naturally, when a tree dies it decomposes slowly releasing carbon over time, during that time new vegetation starts to grow compensating for the carbon being released- carbon neutral. Unnaturally, by burning occurs carbon is immediately released into the atmosphere.

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Changes in the carbon cycle human causes 2

Combustion of Fossil Fuels

FF are natural source of energy and power formed from the dead remans of plants and animals.  When combusted the stored carbon is released primarily as carbon dioxide into the atmosphere. Since the industrial revaluation FF being burnt in increasing quantities, pumping C02 into the atmosphere it enhances the greenhouse effect which consequently increases global temperatures.

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Carbon cycle management stratagies

Modifying industrial combustion- Carbon capture a storage uses technology to capture carbon dioxide emission from coal power stations. Gas is transported to site where it is stored and - prevented from entering the atmosphere (captured). Now the carbon gas is compressed and transported via a pipeline to be injected as a liquid into undergrounf depleted gas feilds. Cuts global emmisons by 19%.

Modifying photosynthesis- plantation forest, are effective at absorbing carbon dioxide compared to natural forest, as they act as carbon sinks removing carbon dioxide from the atmosphere through photosynthesis.

Modifying land use change- carbon farming one type of crop is replaced (rice) by another that has a greater productivity and absorbs more carbon from the atmosphere. 

Modifying deforestation-  consumers are encouraged to only buy wood certified by the FSC. Also, in Malaysia the selective management system is a sustainable approach as trees are selected and replacements are replanted.

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Carbon cycle management stratagies 2

The paris agreement

In 2015, 195 countries adopted the first legally blinding climate deal. Aim to limit the average global temperature increase to 1.5* above pre-industrial times. Meet every five years to set more targets.  Developed nations will support the developing countries aimed at reducing emissions. However, global governance of climate change was unsuscessfull as the US withdrew from the agreement and may not pursue any emission reduction efforts.

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Carbon cycle at different scales


Locally a tree acts as the main carbon store. The seasonal loss of leaves by the deciduous tree creates, leaf litter decomposes and release carbon into the ground which is a process so is the decomposers and plants respiring. Photosynthesis being the only input.


Carbon is an element needed by all plants an animal to survive. The recycling of carbon provides food for plants and animals, and energy sources to be created to fuel industrial development.

The atmosphere is the main store and photosythesesis a process  occurs in aquatic bio mass and terrestial bio mass which a stores. And the biomass on the land decomposes (process) into the soil store which eventually runs off (flow) into the surface of the oceans store, where it diffuses (process) back into the atmosphere store.

Whereas, the biomass in the sea decomposes  (process) into the deep ocenas store. The process of sedimentation occurs and transfer the carbon into carbon deposits in sedimentary rocks which is a store. Then subduction (process) occurs as the sedimentary rocks are subducted in the mantle store and then returns back to the atmposphere via the process of volcanic eruption. 

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Carbon cycle at different scales 2

Time scales

Slow- carbon cycle can take millions of years - the carbon is built up in sedimentary rocks and carbon is released when they are weathered or they are subducted and involved in a volcanic erruption.

Fast carbon cycle can take place within a lifetime- vegetation takes in carbon through photosynthesis and release it through decomposition.

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Carbon cycle as a system

Carbon cycle stores

Carbon stores are the parts of the system where carbon is stored.

  • The main store of carbon is in the lithosphere 70% (rocks and soil), hydrosphere 27% (oceans) and biosphere 1.5% (plant). Carbon stores are not evenly distributed across the world.
  • The largest store of carbon is in the lithosphere, this is in rocks in the ground which contains 100,000 tons of carbon- 70%
  • Store of carbon in the atmosphere 750 billion of metric tons. Carbon is held in the atmosphere in the form of carbon dioxide. The amount of carbon dioxide has increased due to increased carbon emissions from power station, vehicles and deforestation. This has led to the enhanced greenhouse effect. 
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Carbon cycle as a system 2

Carbon cycle processes

These are the link or movement of carbon from one store to another. They include natural processes-  decomposition and human activities- burning fossil fuels.

Weathering-  involves the breakdown or decay of rocks. When C02 is absorbed by rainwater it forms carbonic acid, rocks will slowly dissolve with the carbon being held in a solution. Which is transported away via the water cycle which can then be used to build shells for marine organisms.

Combustion- organic material contains carbon, when it is burned in the presence of oxygen it is converted into energy. This is combustion, it is releasing carbon dioxide in the atmosphere, which returns carbon that might have been stored in rocks for millions of years.

Burial and compaction- is where organic matter is buried and become compacted. Over millions of years these organic sediments form containing carbon form hydrocarbon such as coal and oil. Corals and sheltered organisms take up carbon dioxide from the water and convert it into calcium carbonate which is used to build their shells, when they die shells accumulate on the sea bed and either dissolve which releases C02 and the rest becomes compacted to form limestone which stores C02 for a long time.

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Carbon cycle as a system 3

Carbon cycle processes

Decomposition-when organisms dier they are consumed by decomposers like bacteria and fungi. During decomposition carbon from thei bodies is returned into the atmosphere, some organic material is passed into the soil where it may be stored for a millions of years.

Photosynthesis- this process uses light energy from the sun to produce glucose. Leaves absorb light energy and use it to convert 02 into glucose

Carbon budget

  • The carbon budget describes the amount of carbon that is stored and transferred within the carbon cycle.
  • On a global scale most of the carbon is stored in the lithosphere (in sedimentary rocks) and in the hydrosphere (in the oceans). 
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Carbon cycle as a system 4

The carbon cycle feedback loops-


  • C02 in the atmosphere increases
  • Higher temperature result increasing growing season for plants
  • Plants remove and store C02 from the atmosphere for longer periods.

  • Amount of C02 in the atmosphere is reduced- stored in the soil (less output)


  • Temperature rise
  • Plant respiration increases
  • Amount of C02 in the atmosphere increases
  • Enhanced greenhouse effect- more greehouse gases- temperture rises (more output)                          
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Carbon cycle defintions


Greenhouse effect- natural processes, carbon dioxide, methane and water vapour in the atmosphere slow the loss of the suns energy and warm the planet.

Enhanced greenhouse effect- man made processes, extra carbon dioxide and other greenhouse gases have added to the natural greenhouse effect. Which traps   more of the suns energy meaning the planet gets warmer.

Global warming- gradual rise in average global temperatures caused by enhancing greenhouse effect.

Carbon sink- is a store that absorbs more carbon than it releases.

Carbon source- is a store that releases more carbon than it retains.

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Climate change

Evidence of climate change

Factors causing climate change

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Carbon cycle impacts

Consequences of increased levels of carbon in the:


  • In the ocean 30 percent of the carbon dioxide people have put into the atmosphere has diffused into the ocean through the direct chemical exchange.
  • Dissolving carbon dioxide in the ocean creates carbonic acid, which increases the acidity of the water.
  • Ocean acidification affects marine organisms, first carbonic acid reacts with carbonate ions in the water to form bicarbonate.
  • However, those same carbonate ions are what shell-building animals like coral need to create calcium carbonate shells.
  • With less carbonate available, the animals need to expend more energy to build their shells. As a result, the shells end up being thinner and more fragile (reducing the carbon store in the oceans).
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Carbon cycle impacts 2

Consequences of increased levels of carbon on:


  • More wildfires are controlled as they threaten human settlements. This increases the build-up of ‘woody’ plant material which increases the carbon store in the lithosphere.
  • Fires and deforestation in other locations have increased atmospheric carbon dioxide levels in the atmosphere
  • Some farmland in HICs has been replaced by forests. Higher incomes allow food to be imported rather than grown locally. Trees store more carbon than crops this increases the carbon store in the lithosphere.
  • Higher temperatures in cold tundra climates increase the rate of decomposition of DOM and the release of more carbon into the atmosphere.
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Carbon cycle case study

Amazon Rainforest


  • South America, mostly in Brazil - between tropics
  • Largely between 5 degrees north and 20 degrees south.


  • High biodiversity
  • Most productive biome on the planet. 5
  • Trees in distinct layers – shrub layer, under canopy, canopy and emergents.


  • High precipitation – 2000mm
  • Constant high temperatures – 27 degrees Celsius
  • Daily weather pattern with temperatures rising in AM then convectional rainfall in PM
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Carbon cycle case study 2

Carbon cycle:

  • This means that carbon is stored in large amounts – 2100g C/M2 per year. TRF is a carbon sink.
  • Respiration by plants and decomposition of DOM leads to some CO2 returning to the atmosphere.
  •  Carbon stored in soils can also leave the TRF biome via rivers. This is an output.

Deforestation of the Amazon rainforest

  • The removal of trees without adeqaute replanting.


  • Valuable hardwoods (timber) harvested for sale in HICs. Used for construction and furniture. 
  • Population increase leads to an increase in demand for land to live on.
  • Population growth increases demand for food in LICs. 
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Carbon cycle case study 3


  • Photosynthesis is reduced – unless other plants colonise or are introduced to the area. However they are likely to be less productive and so photosynthesis is permanently reduced.
  • Ash may also be washed into rivers taking carbon out of the TRF system as an output. The TRF is no longer a carbon sink and may be a carbon source for a period.
  • Decomposers and respiration will also be much reduced. Less carbon is emitted.
  • Forest burning adds carbon to the atmosphere as well as reducing the TRF capacity to absorb carbon. 


  • Alley cropping-  An approach in which fast growing trees are planted in rows to provide shade in between the rows to reduce weeds. In time crops can be planted in these spaces. Allows land to regain an element of fertility and for trees to provide habitats this is environmentally sustainable. 
  • Government backed nature reserves and national parks- an approach in which TRF are protected and conserved for future generations. No exploitation is allowed. 

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very good revision source . Thanks!!

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