CGP The Carbon Cycle

• Carbon is an element, and a really important one at that
• Where carbon is found

  • Organic stores (living things)
  • Inorganic stores (rocks, gases, fossil fuels)
• Carbon can be found in each of the Earth's systems in some form or another
• Earth's systems

  • Lithosphere
  • Hydrosphere
  • Cryosphere
  • Atmosphere
  • Biosphere
• Lithosphere

  • Over 99.9% of the carbon on Earth is stored in sedimentary rocks such as limestone
  • About 0.004% of the carbon on Earth is stored in fossil fuels, such as coal and oil
• Hydrosphere

  • Carbon dioxide (CO2) is dissolved in rivers, lakes and oceans
  • The oceans are the second-largest carbon store on Earth, containing approximately 0.04% of the Earth's carbon. The majority of carbon here is found deep in the ocean in the form of dissolved inorganic carbon. A small amount is found at the ocean surface where it is exchanged with the atmosphere.
• Cryosphere

  • The cryosphere contains less than 0.01% of Earth's carbon
  • Most of the carbon in the cryosphere is in the soil in areas of permafrost (permanently frozen ground) where decomposing plants and animals have frozen into the ground
• Atmosphere


  • Carbon is stored as carbon dioxide (CO2) and in smaller quantities as methane (CH4) in the atmosphere
  • The atmosphere contains about 0.001% of the Earth's carbon
• Biosphere

  • Carbon is stored in the tissues of living organisms
  • It is transferred to the soil when living organisms die and decay
  • The biosphere contains approximately 0.004% of the Earth's total carbon
• The carbon cycle

  Carbon is stored and transferred
• The carbon cycle is a closed system - there are inputs and outputs of energy, but the amount of carbon in the system remains the same
• Some carbon is locked away in long-term stores, e.g. rock and fossil fuels deep underground
• Major stores and flows in the carbon cycle

  • Fossil fuels
  • Atmosphere
  • Vegetation
  • Earth's crust
  • Ocean
• Photosynthesis


  1. Transfers carbon stored in the atmosphere to biomass

  2. Plants and phytoplankton use energy from the Sun to change carbon dioxide and water into glucose and oxygen
• Combustion


  Transfers carbon stored in living, dead or decomposed biomass (including peaty soils) to the atmosphere by burning
• Ocean uptake and loss

  1. CO2 is directly dissolved from the atmosphere into the ocean

  2. Carbon is also transferred to the oceans when it is taken up by organisms that live in them (e.g. plankton)

  3. Carbon is transferred from the ocean to the atmosphere when carbon-rich water from deep in the ocean rises to the surface and releases CO2
• Respiration


  1. Transfers carbon from living organisms to the atmosphere

  2. Plants and animals break down glucose for energy, releasing carbon dioxide and methane in the process
• Decomposition


  1. Transfers carbon from dead biomass to the atmosphere and the soil

  2. After death, bacteria and fungi break organisms down, releasing CO2 and methane
• Chemical weathering

  1. Transfers carbon from the atmosphere to the hydrosphere and biosphere

  2. Atmospheric carbon reacts with water vapour to form acid rain. When this acid rain falls onto rocks, a chemical reaction occurs which dissolves the rocks. The molecules resulting from this reaction may be washed into the sea, where they react with CO2 dissolved in the water to form calcium carbonate, which is used by marine creatures to make shells.
• Sequestration

  Carbon from the atmosphere can be captured and held in sedimentary rocks or as fossil fuels. Rocks and fossil fuels form over millions of years when dead animal and plant material in the ocean falls to the floor and is compacted.
• Fast carbon flows

  • Quickly transfer carbon between sources (minutes, hours or days)
  • Examples: photosynthesis, respiration, combustion, decomposition
• Slow carbon flows

  Sequestration - takes millions of years for carbon to be sequestered in sedimentary rocks
• The carbon flows taking place also depend on spatial scale
• Wildfires

  • Rapidly transfer large quantities of carbon from biomass for soil to the atmosphere
  • Loss of vegetation decreases photosynthesis, so less carbon is removed from the atmosphere
  • In the longer term, fires can encourage the growth of new plants, which take in carbon from the atmosphere for photosynthesis. Depending on the amount and type of regrowth, fires can have a neutral effect on the amount of atmospheric carbon.
• Volcanic activity


  • Carbon stored within the Earth in magma is released during volcanic eruptions, with the majority entering the atmosphere as CO2
  • Recent volcanic eruptions have released much less CO2 than human activities, but there is the potential for a very large eruption to disrupt the carbon cycle significantly
• Human impact on the carbon cycle

  • Since the industrial revolution, the impact that humans have on the carbon cycle has increased hugely
  • We're currently causing carbon flows from the lithosphere and biosphere to the atmosphere to happen much faster than they would naturally
• Main human causes of change to the carbon cycle


  • Hydrocarbon fuel extraction and use
  • Farming
  • Deforestation
  • Land use changes
• Carbon budget


  The difference between the inputs of carbon into a subsystem and outputs of carbon from it
• If the outputs of carbon outweigh the inputs, the subsystem acts as a carbon source. If the inputs of carbon outweigh the outputs, the subsystem acts as a carbon sink.
• Changes to the carbon cycle


  Can have significant impacts on the atmosphere, land and oceans
• Impacts on the atmosphere and climate

  • The carbon cycle affects the amount of gases containing carbon (e.g. CO2 and methane) in the atmosphere
  • These are greenhouse gases that trap some of the Sun's energy, keeping the planet warm
  • As the concentrations of greenhouse gases in the atmosphere increase due to human activities, temperatures are expected to rise, causing global warming
  • Changes in temperature can affect other aspects of the climate, e.g. more intense storms
• Impacts on the land

  • The carbon cycle allows plants to grow - if there was no carbon in the atmosphere, plants could not photosynthesize
  • Changes in the carbon cycle can reduce the amount of carbon stored in the land, e.g. warmer temperatures caused by global warming are causing permafrost to melt, releasing carbon previously stored
• Impacts on the oceans

  • Carbon dioxide is dissolved directly into the oceans from the atmosphere
  • CO2 in oceans is used by organisms such as phytoplankton and seaweed during photosynthesis and by other marine organisms to form calcium carbonate shells and skeletons
  • Increased levels of CO2 in the atmosphere can increase the acidity of the oceans, which can have adverse effects on marine life
  • Global warming can also affect oceans, e.g. organisms sensitive to temperature may not be able to survive at higher temperatures