AQA Geography - Carbon Cycle

Carbon Cycle
It is the complex processes carbon undergoes as it is transformed from organic carbon (the form found in living organisms such as trees and plants) to inorganic carbon and back again.
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what does the Carbon Cycle show?
carbon cycle shows how carbon moves from the atmosphere, through various animals and plants, then back into the atmosphere again.
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what is carbon?
Carbon is one of the most chemically versatile elements. It forms more compounds than any other element. It is found in all life forms as well as sedimentary rocks, diamonds, graphite, coal, oil and gas.
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What are the main stores of carbon?
the lithosphere, hydrosphere, cryosphere, atmosphere and biosphere.
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carbon sink
a store that absorbs more carbon than it releases.
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carbon source
A carbon source releases more carbon than it absorbs.
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Carbon Transfers
These are processes that transfer carbon between the stores. Transfers such as inputs and outputs affect the size of the carbon stores.
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Carbon units of measurement
A gigatonne of carbon dioxide is used to measure the amount of carbon in stores 1GtC = 109 tonnes (1 billion tonnes)
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Anthropogenic Co2
Carbon dioxide generated by human activity
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Carbon Sequestration
The capture of carbon dioxide (Co2) from the atmosphere or capturing anthropogenic Co2 from large scale stationary sources like power plants before it is released into the atmosphere. Once captured it can be put into long term storage
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Greenhouse Gas
Any gaseous compound in the atmosphere that is capable of absorbing infrared radiation, thereby trapping and holding heat in the atmosphere
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The breakdown of rocks in situ by a combination of weather, plants and animals
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main carbon stores
Marine sediments and sedimentary rocks Ocean Fossil fuel deposits Soil organic matter Atmosphere Terrestrial plants
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Stores or stocks
are the total amount of the material of interest held within a part of the system. This is effectively how much of the material there is and where it is.
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are measurements of the rate of flow of material between the stores. Because fluxes are a rate the units are mass per unit time, commonly for global cycles these are expressed as Pg per year.
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are the physical mechanisms which drive the flux of material between stores. For example one of the key processes which drive the flux of carbon from the atmosphere to the vegetation store is photosynthesis.
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How does carbon move from one store to another?
Carbon moves from one store to another in a continuous, closed system The processes by which the carbon moves between these stores are known as transfers or fluxes
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Can you remember the difference between a source and a sink?
If more carbon enters a store than leaves it, it is considered a net carbon sink, whereas if more carbon leaves than enters the store, it is considered a net carbon source.
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what are the three exchanges
Plant Sere (eg lithosphere) and Continental
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This involves the breakdown or decay of rocks in situ (where they are) on or close to the surface As the rock breaks down, the carbon stored within it is returned to the carbon cycle. When carbon dioxide is absorbed by rainwater it forms an acid
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Burial and compaction
Organic matter dies and is buried by sediments and becomes compacted. Over millions of years, these organic sediments (which contain carbon) under the right conditions form hydrocarbons, such as oil and coal.
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Burial and compaction example
An example of this is corals and shelled organisms take up carbon dioxide from the water and covert it into calcium carbonate to build up their shells. When they die, the shells accumulate on the sea bed. These become compacted to form limestone, st
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Process whereby plants use light energy from the sun to produce carbohydrates in the form of glucose
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The is the opposite of photosynthesis Plants use the carbohydrates they store as an energy source to carry out life functions. Consumers such as animals and bacteria then eat them and get their energy from plants and convert it into energy.
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When organisms die they are consumed by decomposers such as bacteria, fungi and earthworms. During this process of decomposition, carbon from their bodies is returned to the atmosphere is carbon dioxide.
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Organic material contains carbon. When it is burned in the presence of oxygen (Eg coal in a power station) it is converted into energy, carbon dioxide and water. This is known as combustion.
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Carbon sequestration
It is an umbrella term used to describe the transfer of carbon from the atmosphere to the plants, soils, rock formations and oceans.
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what is the advantage of ocean carbon sequestration?
is that is “sinks” to great depths within weeks or months of being captured at the surface.
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Terrestrial or biological sequestration
This involves the use of plants to capture CO2 from the atmosphere. Carbon is then stored in the stems and roots of the plants (as well as in the soil).
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Terrestrial or biological sequestration benifits
There is also the added benefit of the enrichment of plant ecosystems & associated wildlife habitats.
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Terrestrial or biological sequestration negatives
a forest may lose carbon through a catastrophic forest fire OR if the forest suffers disease/infestation. land-based sequestration plantations are slow growing and require monitoring/management which lasts the lifetime of the plantation
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Why has volcanic activity contributed very little? (Studies suggest that volcanoes have produced less that 1% of the CO2 released currently by human activity)
Sulphur dioxide, which is converted to sulphuric acid, forms droplets which reflect radiation from the sun back into space (albedo) cooling the Earth’s lower atmosphere.
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What is forests use in the carbon cycle?
Forests are a carbon sink, through the process of photosynthesis trees absorb CO2
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what happens if they are burnt by forest fire?
If they are burnt by forest fire, their carbon is released back into the air as CO2
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Benefits of forest fires
Forest fires can be critical for new growth and rejuvenation in a forest, as nutrients are returned to the soil and new saplings can grow. This new vegetation reabsorbs much of the CO2 that the fire released, providing a natural balance and negative
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where does most of the world’s gas and oil come from?
Most of the world’s gas and oil comes from rocks that are 70-11 million years old
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Fossil fuel combustion of the cement industry
produces 5% of all human-induced global CO2 emissions; 50% of which comes from the heating of the calcium carbon and 40% from the burning of fuel to power the process.
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what are the three most used fossil fuels in order?
43% coal 33% oil 18% gas
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how do Farming practices affect the carbon cycle?
When soil is ploughed, the soil layers mix. As a result, soil microbial activity dramatically increases, resulting in more soil organic matter being decomposed. As a result, more carbon is lost to the atmosphere.
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What is the greatest source of carbon emissions in agriculture?
is enteric fermentation (the methane belched by livestock during digestion). In 2011, this made up 39% of all agricultural carbon emissions. Furthermore, this figure increased 11% between 2001 and 2011.
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How much deforestation a year?
Around 13 million hectares of forest are cut down and changed to other land uses every year.
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what does forest clearing accerates?
Forest clearing accelerates the decay of dead wood, litter and below-ground organic carbon.
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What is the carbon budget?
The carbon budget uses data to describe the amount of carbon that is stored and transferred within the carbon cycle (similar to a household budget – what is coming in and out)
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where is the vast majority of carbon stored?
is stored in the crust and in the oceans. Relatively low amounts are stored in the atmosphere and in plants. This is because the transfers are extremely active – carbon constantly flows back and forth between these stores.
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How do greenhouse gases work?
gases absorb long-wave radiation from the earth and lower atmosphere, which enables life to exist on Earth. This is known as the greenhouse effect
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Enhanced greenhouse effect
The impact on the climate from the additional heat retained due to increased amounts of carbon dioxide and other GHGs that humans have released into the atmosphere since in the industrial revolution.
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Radiative forcing
The difference between the incoming solar energy absorbed by the earth and energy radiated back to space
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Soil organic carbon (SOC)
The organic constitutes in the soil; tissues from dead plants and animals, products produced as these decompose and the soil microbial biomass.
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Impacts of the carbon cycle on the land
Increases Photosynthesis, When temperatures increased permafrost starts to thaw (This results in a positive feedback loop)
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Impacts of the carbon cycle the Ocean
It is difficult to predict the precise rate, magnitude and direction of change of Co2 uptake and how it affects acidity, salinity, storminess and nutrient enrichment
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How is carbon used/ stored in the ocean?
Carbon can be converted into calcium carbonate, which is used by some marine organisms to build shells.
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Ocean acidification
30% of the released Co2 is diffused into the ocean through direct chemical exchange. This creates a carbonic acid, making the ocean less alkaline Carbonic acid reacts with carbonate ions in the water to form bicarbonate.
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Impacts of Ocean acidification
, animals like coral and phytoplankton need those ions to make their shells. Less carbonate available may mean shells become thinner and more fragile. Coral reefs provide food and livelihood security for 500 million people.
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Postives of Ocean acidification
the more acid seawater is, the better it is at dissolving calcium carbonate rocks (chalk and limestone). Over time, this allows the ocean to soak up excess co2 because the more acidic water will dissolve more rock.
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Melting sea ice mechanism?
Melting ice is part of a feedback mechanism: Highly reflective ice is replaced by more absorbent water. This then absorbs more sunlight which in turn amplifies the warming.
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Melting sea ice impacts
Sea ice also provides a habitat for algae. The loss affects the food chain from krill to bears. Seals and bears can no longer travel on the ice. Huge consequences for sea level rise
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Sea level rise Since the 1990s?
sea levels have risen at a rate of 3.5mm/year.
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Melting terrestrial ice
warmer temperatures mean increased rate of ice melting in summer and reduced snowfall in winter This results in a imbalance  net gain of water entering the ocean.
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Thermal expansion
When water heats up, it expands: About half of the past century’s rise in sea level is attributed to the oceans having a greater volume.
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Ocean Salinity
Decrease in salinity in the deep North Atlantic More freshwater being added to the ocean
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Impacts of the carbon cycle on the atmosphere and global climate
Proportion is now 400ppm, higher than at any change in the last 800,000 years and is set to increase further. This has led to enhanced greenhouse effects.
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A return or knock on effect that usually leads to a change in the effectiveness of one or more processes in a cycle
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positive feedback
enhances and leads to a continuation of the outcome
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Negative feedback
reduces the outcome leading to stability and equilibrium being restored
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What is the role of water and carbon?
Both water and carbon are crucial in supporting life on earth. In people, carbon is stored as glucose and carbon assists cellular respiration. In trees, the carbon content of leaves and woody matter is approximately 50%.
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How do water and carbon cycles interact in the atmosphere to influence climate?
All living organisms need water to survive – drinking, irrigation, power and energy. Carbon is essential for plant growth as well as an important GHG that absorbs long wave radiation, providing sufficient atmospheric warmth for live to occur.
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Relationship between water and carbon cycles
An important link between the water cycle and the carbon cycle is the ability of water to absorb and transfer Co2.
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How are the water and carbon cycle impacted upon by climate change?
Increased Co2 is warming the atmosphere. This then results in higher evaporation rates and a wetter atmosphere. This leads to a positive feedback situation of further warming.
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Marine Phytoplankton feedback loop (Negative feedback loop.)
Warmer temperatures  Increases in phytoplankton  increase in clouds  global cooling.
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Climate Change Mitigation
refers to efforts to reduce or prevent emission of greenhouse gases. Mitigation can mean using new technologies and renewable energies, making older equipment more energy efficient, or changing management practices or consumer behaviour.
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Carbon capture and storage (CCS)
uses technology to capture carbon dioxide emissions from coal-fire power stations and industry. The gas is then transported to a site where it can be stored and prevented from entering the atmosphere.
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Carbon capture and storage (CCS) on global emissions
This could cut global emissions by up to 19%.
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Boundary Dam, Canada positives
Aims to cut co2 emissions by 90% - equivalent to 250,000 (1 million tonnes a year).
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Boundary Dam, Canada negatives
Economic viability – relies on reservoirs being empty. Very costly Unsure of the future implications of places such large amounts underground.
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Soil carbon storage in grasslands can be improved by...
Avoidance of overstocking of grazing animals Adding manures and fertilisers that have a direct impact on soil organic carbon (SOC) levels through the added organic material. Revegetation – Improved pasture and legumes can increase productivity
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Political initiatives on climate change
Establishment of the IPCC (1988) Kyoto (1997) The Paris agreement (2015)
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Intergovernmental Panel on climate change – scientists and experts set up to monitor, analyse climate
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The Paris agreement (2015)
At the Paris climate conference (COP21) in December 2015, 195 countries adopted the first legally binding global climate deal, due to be enforced by 2020. Aim to limit the average global temperature increase to 1.5oC above pre-industrial levels.
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Card 2


what does the Carbon Cycle show?


carbon cycle shows how carbon moves from the atmosphere, through various animals and plants, then back into the atmosphere again.

Card 3


what is carbon?


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Card 4


What are the main stores of carbon?


Preview of the front of card 4

Card 5


carbon sink


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