Carbon Cycles

• Outline the global distribution and sizes of the major stores of carbon - lithosphere.


  Lithosphere - Over 99.9% of Earth's carbon is stored in sedimentary rocks such as limestone. About 0.004% of Earth's carbon is stored in fossil fuels, such as coal and oil, in the lithosphere.
• Outline the global distribution and sizes of the major stores of carbon - atmosphere.


  Carbon is stored as carbon dioxide and methane in the atmosphere. The atmosphere contains about 0.001% of Earth's carbon.
• Outline the global distribution and sizes of the major stores of carbon - hydrosphere.

  Carbon dioxide is dissolved in rivers, lakes and oceans. Oceans contain about 0.04% of the Earth's carbon, the majority of which is found deep in the ocean in the form of dissolved inorganic carbon. A small amount is found at the ocean's surface where it is exchanged with the atmosphere.
• Outline the global distribution and sizes of the major stores of carbon - biosphere.

  Carbon is stored in the tissues of living organisms. It is then transferred to the soil when living organisms die and decay. The biosphere contains about 0.004% of the Earth's carbon.
• Outline the global distribution and sizes of the major stores of carbon - cryosphere.

  Most carbon found in the cryosphere is found in permafrost in the soil where decomposing plants and animals have frozen into the ground. The cryosphere contains about 0.01% of the Earth's carbon.
• Describe how photosynthesis acts as a carbon flow.

  Photosynthesis transfers carbon stored in the atmosphere to biomass. Plants and phytoplankton use energy from the sun to change water and carbon dioxide into glucose and oxygen, allowing them to grow. Carbon is passed through the food chain and released through respiration and decomposition.
• Describe how respiration acts as a carbon flow.

  Respiration transfers carbon from living organisms to the atmosphere. Plants and animals break down glucose for energy, releasing carbon dioxide and methane in the process.
• Describe how combustion acts as a carbon flow.

  Combustion transfers carbon stored in living, dead or decomposed biomass to the atmosphere by burning. Wildfires cause carbon flow.
• Describe how decomposition acts as a carbon flow.


  Decomposition transfers carbon stored in dead biomass to the atmosphere and soil. After death, bacteria and fungi break organisms down, releasing carbon dioxide and methane in the process. Some carbon is transferred to the soil in the form of humus.
• Describe how ocean uptake and loss acts as a carbon flow.

  CO2 is directly dissolved into the ocean from the atmosphere. It is also transferred into the ocean when it is taken up by organisms (e.g. plankton) that live in them. Carbon is also transferred when carbon-rich water from deep below rises to the surface and releases CO2.
• Describe how weathering acts as a carbon flow.

  Chemical weathering transfers carbon from the atmosphere to the hydrosphere and biosphere. Atmospheric carbon reacts with water vapour to form acid rain. When acid rain falls onto rocks, a chemical reaction occurs, dissolving them. The molecules resulting from this reaction can be washed up by seawater and react with the dissolved CO2 to form calcium carbonate, a substance which is used by sea creature to, for example, make shells.
• Describe how sequestration acts as a carbon flow.

  Carbon from the atmosphere can be sequestered (captured and held) in sedimentary rocks or as fossil fuels. Rocks and fossil fuels form over millions of years when dead plant and animal material in the ocean falls onto the ocean floor and is compacted. Carbon is sequestered until it is burnt (combustion).
• Define carbon budget.


  The balance between the inputs and outputs of carbon.
• Give an example of a carbon budget.


  In the atmosphere, inputs of carbon come from burning fossil fuels and volcanic eruptions and outputs come from sequestration and decomposition.
• Explain what is a carbon source.

  When the outputs of carbon are more than the inputs, releasing more carbon than absorbed.
• Explain what is a carbon sink.

  When the inputs of carbon are more than the outputs, absorbing more carbon than released.
• How do changes in the carbon cycle affect the atmosphere and climate?

  Changes in the carbon cycle affect the amount of gases containing carbon (e.g. CO2 and methane) in the atmosphere. These gases trap some of the Sun's heat and warm the earth.

  As human activities like deforestation and the burning of fossil fuels lead to the increase of greenhouse gases in the atmosphere, temperatures are expected to rise.

  This is global warming, and it can affect other aspects of the climate, e.g. more intense storms are predicted.
• How do changes in the carbon cycle affect the oceans?

  Carbon dioxide is dissolved from the atmosphere into the oceans as a part of the carbon cycle.

  CO2 in oceans is used by marine organisms like phytoplankton and seaweed through photosynthesis to make calcium carbonate shells and skeletons.

  Increased levels of CO2 can lead to increased levels of acidity in the oceans, as the oceans initially absorb more CO2. This can have adverse effects on marine life.

  Increased global temperatures could mean that marine life sensitive to temperature such as phytoplankton cannot survive in the oceans. This causes their numbers to decrease, and so less CO2 is absorbed from the atmosphere because less is needed for them for photosynthesis.

  Warmer water is less able to absorb CO2, so as temperatures rise less CO2 is dissolved into the oceans.
• How can wildfires change the magnitude of carbon stores?

  They can release large amounts of carbon stored in biomass into the atmosphere.

  By destroying vegetation, less carbon is absorbed from the atmosphere by plants through photosynthesis.

  In the long term, fires can encourage the regrowth of plants. This takes in more carbon from the atmosphere through photosynthesis. Depending on the amount and type of regrowth, wildfires can have a neutral effect on the amount of atmospheric carbon.
• How can can volcanic activity change the magnitude of carbon stores?

  Carbon held within the earth in magma is released during volcanic eruptions, most of it entering the atmosphere as CO2.

  Recent eruptions have released less CO2 than human activities, but a very large one could affect the carbon cycle significantly.
• How can extracting and burning hydrocarbons impact the carbon cycle?


  Extracting and burning fossil fuels releases CO2 into the atmosphere.

  Without the lithosphere, the carbon would remain sequestered in the lithosphere for thousands or millions of years to come.
• How can deforestation impact the carbon cycle?

  Forests may be cleared for agriculture, logging or to make way for developments.

  Clearance of trees reduces the size of this carbon store and if they are burned there is also a rapid transfer of carbon from the biosphere to the atmosphere.
• How can farming practices impact the carbon cycle?

  Animals release CO2 and methane when they respire and digest food.

  Ploughing can release CO2 stored in soil.

  Growing rice in rice paddies releases methane.
• What has enhanced the effect that farming practices have on the carbon cycle?

  Due to population increase, there has been a higher demand for food, so carbon emissions from food production has increased.

  The mechanisation of farming has also increased CO2 emissions.
• How can land use changes impact the carbon cycle?

  The change to urban land use has lead to vegetation being removed to make way for buildings, reducing carbon storage in the biosphere.

  When urban areas expand, lots of concrete is used, which releases CO2 when it is produced.
• Why are water and carbon stores and cycles essential for life on earth?

  All living things contain carbon and water - carbon is a basic building block for life.

  Plants form the base of most food chains - plants use photosynthesis to turn CO2 and water into biomass.
• Outline the relationship between the water and carbon cycle in the atmosphere.

  Water is present in the atmosphere as water vapour and carbon as CO2 and methane. These are greenhouse gases and they cause a natural greenhouse effect that prevents some heat from escaping into space and keeps it within the earth's atmosphere. This means that the earth's temperature isn't too hot to be uninhabitable.
• What is the IPCC and what does it do?

  An international organisation set up by the UN that plans to reduce carbon emissions from human activities to prevent large temperature rises.
• What can people do on an individual scale to mitigate the impacts of climate change?

  People can choose to use their cars less and buy more fuel efficient cars.

  They can make their homes more energy efficient with insulation and double glazing.
• What can be done at a regional and national scale to mitigate the impacts of climate change?

  Governments can reduce reliance on fossil fuels by increasing the availability and reducing the cost of renewable energy sources

  Afforestation can increase carbon uptake from the atmosphere into the biosphere.

  Planners can increase the sustainability of developments by improving public transport and creating more green spaces.

  Government can invest in CCS. CO2 in the atmosphere is captured and stored underground, e.g. in depleted oil and gas reservoirs.
• What can be done on a global scale to mitigate the impacts of climate change?

  Countries can work together to reduce emissions. E.g. the Kyoto Protocol (1997) and Paris Agreement (2015) set out to reduce global emissions.

  International carbon trading schemes limit the amount of emissions that businesses and countries can produce.
• Give a brief introduction of the Amazon rainforest.

  The world's largest tropical rainforest with a hot, wet climate with dense vegetation.

  It is home to many indigenous people and up to 1 million plant species, over 500 species of mammals and over 2000 species of fish.
• Describe the role the water cycle plays in the Amazon environment.

  The water cycle causes the Amazon to be very wet - there is a lot of evaporation over the Atlantic Ocean which is blown towards the Amazon, leading to the high levels of rainfall.

  Warm temperatures mean that evaporation in the rainforest itself is also very high, further increasing the rainfall.

  The rainforest has a dense canopy, leading to high interception. This means that there is less water flowing into rivers.

  The water cycle affect the animal life - it is populated with species adapted to high humidity and rainfall.
• Describe the role the carbon cycle plays in the Amazon environment.

  The Amazon stores lots of carbon in vegetation and soil, so it is a carbon sink.

  The increase concentration of CO2 in the atmosphere has increased the productivity of the rainforest as there has been more CO2 for photosynthesis, so the biomass has increased. This also means that the amount of carbon the Amazon has sequestered has also increased.

  However, it has been suggested that trees are dying younger, so the rainforest may not be reliable as a carbon store in the future.
• How is deforestation affecting the Amazon rainforest?

  It affects the water cycle as, in deforested areas, there is not canopy cover to intercept rainfall, increasing the amount of rainwater reaching ground surface, leading to more surface runoff, increasing risk of flooding.

  It affects the carbon cycle as, without roots to stabilize the soil, the carbon-rich surface layer of soil is washed away, and the carbon is transferred into the hydrosphere. Also, deforestation decreases leaf litter, so humus isn't formed. The soil cannot support much new growth, limiting the amount of potential carbon storage.
• How is climate change affecting the Amazon rainforest?

  Temperature increases and rainfall decreases can lead to drought. The Amazon had severe droughts in 2005, 2010 and 2015.

  Plants and animals in the Amazon are adapted to living in wet conditions, so many species die in dry weather.

  Scientists predict a 4 degree rise in temperature could kill 85% of the Amazon rainforest.
• How does selective logging aim to limit human impacts on the Amazon?

  Only some trees, like the oldest ones, are felled.

  If only a few trees are removed, the canopy's structure remains and the soil isn't exposed.

  This means the forest is able to regenerate, so the impact on the water and carbon cycle in minimal.
• How does replanting aim to limit human impacts on the Amazon?

  New trees are planted to replace the ones that are cut down. For example, a project in Peru replanted 115 acres of forest between 2016 and 2019.
• How does environmental law aim to limit human impacts on the Amazon?

  Laws can help protect rainforests. For example, laws that control land use, like the Brazilian Forest Code that says that landowners have to keep 50-80% of their land as forest.
• How does protection aim to limit human impacts on the Amazon?

  Countries have set up national parks and nature reserves to protect rainforests. For example, the Central Amazon Conservation Complex was set up in 2004 to protect biodiversity.