carbon cycle

Question 1

where is carbon found?

Answer 1

• carbon can be found in organic and inorganic stores
• organic - carbon is found in living things
• inorganic - carbon is found in non living things e.g. rocks

lithosphere:
- over 99.9% of carbon on earth is stored in sedimentary rocks such as limestone
- 0.004% is stored in fossil fuels

hydrosphere:
- carbon dioxide is dissolved in rivers, lakes and oceans
- oceans are the 2nd largest store of carbon on earth —> the majority of carbon is found deep in the ocean

biosphere:
- 0.004% of earths total carbon is found in living organisms —> when organisms die and decay, this carbon is transferred to the soil (pedosphere)

atmosphere:
- carbon is stored in the atmosphere as CO2 and methane
- the atmosphere contains around 0.001% of the earths carbon

cyrosphere:
- less than 0.01% of earths carbon is stored in the cryosphere

Question 2

carbon cycle stores and flows

Answer 2

• Carbon cycle - process by which 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

Flows of carbon:

Photosynthesis:
- Photosynthesis transfers carbon stored in the atmosphere to biosphere - enables plants to grow
- Carbon is passed through the food chain

Combustion:
- Combustion transfers carbon stored in living, dead or decomposed biomass to the atmosphere by burning

Ocean uptake and loss:
- CO2 is directly dissolved from the atmosphere into the ocean. It is also taken up by organisms that live in them e.g. plankton
- Carbon is also transferred from the ocean to the atmosphere when carbon-rich water from deep in the oceans rises to the surface and releases CO2

Sequestration:
- Carbon from the atmosphere can be sequestered (captured and held) in sedimentary rocks. Rocks form over millions of years when dead animal and plant material in the ocean falls to the floor and is compacted

Respiration:
- Respiration transfers carbon from living organisms to the atmosphere

Decomposition:
- Decomposition transfers carbon from dead biomass to the atmosphere and the soil (pedosphere)
- After death, bacteria and fungi break organisms down. CO2 and methane are released
- Some carbon is transferred to the soil in the form of humus

Weathering:
- Chemical weathering transfers carbon from the atmosphere to the hydrosphere and biosphere
- 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. Here, they react with CO2 dissolved in the water to form calcium carbonate, which is used by sea creatures e.g. to make shells

Fast carbon flows:
- Fast carbon flows quickly transfer carbon between sources. It only takes a matter of minutes, hours or days
- Photosynthesis, respiration, combustion and decomposition are examples of fast carbon flows

Slow carbon flows:
- Sequestration is a slow carbon flow. It takes millions of years for carbon to be sequestered in sedimentary rocks

Question 3

physical factors that affect the carbon cycle

Answer 3

climate
colder temperatures:
- lower temps —> less photosynthesis —> plant growth decreases —> less CO2 absorbed
- colder oceans absorb more CO2 from the atmosphere
warmer temperatures:
- higher temps —> more photosynthesis —> increased plant growth —> more CO2 absorbed
- warmer oceans absorb less CO2 from the atmosphere —> more CO2 in atmosphere

wildfires
- short term: (wildfires lead to more carbon being released into the atmosphere) loss of vegetation —> photosynthesis decreases —> less carbon removed from the atmosphere
- long term: (wildfires lead to less carbon being released into the atmosphere) soil can become more fertile after wildfires —> encourages the growth of new plants —> plants take in carbon from the atmosphere for photosynthesis

volcanic activity
- carbon stored within the earth is released during volcanic eruptions —> carbon is transferred from the lithosphere to the atmosphere
- recent volcanic eruptions have released much less CO2 than human activities

Question 4

human factors that affect the carbon cycle

Answer 4

fossil fuel extraction and use:
- extracting and burning fossil fuels: we need fossil fuels for many things e.g. heating up housing and powering vehicles etc —> this releases CO2 into the atmosphere
- as population has increased overtime, fossil fuel use has increased overtime

deforestation:
- forests may be cleared for agriculture, logging, or to make space for housing —> reduces size of carbon stores —> less carbon can be stored in trees and more carbon will enter the atmosphere
- a lot of the deforested trees are burnt —> releases CO2 (rapid flow of carbon from biosphere to atmosphere)

urbanisation:
- due to urbanisation, more houses have to be built —> trees are removed to make way for buildings (reduces carbon storage in the biosphere) —> reduces size of carbon stores —> less carbon stored in trees and more carbon will enter the atmosphere
- lots of concrete is used when urban areas expand —> concrete production releases lots of CO2 —> releases CO2 into the atmosphere

farming:
- population has increased —> food production has increased —> carbon emissions from farming practises have increased e.g. growing rice in rice paddies releases a lot of methane —> more carbon stored in the atmosphere// animals release CO2 and methane into the atmosphere when they respire and digest food —> carbon moves from the biosphere to the atmosphere

Question 5

carbon budget

Answer 5

• The carbon budget is the difference between the inputs and outputs of carbon of a subsystem
• For example, in the atmosphere, inputs of carbon come from volcanic eruptions, burning fossil fuels, respiration and ocean loss, and outputs occur through photosynthesis, sequestration, chemical weathering and ocean uptake
  3. The balance of the inputs and outputs of a subsystem determines whether it acts as a carbon source (the outputs of carbon outweigh the inputs, so it releases more carbon than it absorbs) or a carbon sink (the inputs of carbon outweigh the outputs, so it absorbs more carbon than it releases)

Question 6

atmosphere, land, oceans

Answer 6

When there’s a change to the carbon cycle, it can have significant impact on the atmosphere, land and oceans:

Atmosphere and climate:
- As the concentrations of greenhouse gases in the atmosphere increase (e.g. due to changes in the carbon cycle caused by human activities such as deforestation and the burning of fossil fuels) temperatures are expected to rise. This is global warming
- Changes in temperature across the globe will affect other aspects of the climate e.g. more intense storms are predicted

Land:
- 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. This releases carbon previously stored in the permafrost into the atmosphere
- An increase in global temperatures could also increase the frequency of wildfires

Oceans:
- CO2 in oceans is used by organisms such as phytoplankton and seaweed during photosynthesis and by other marine organisms to form calcium carbonate shells
- Increased levels of CO2 in the atmosphere can increase the acidity of the oceans. This can affect marine life
- Global warming can also affect oceans. For example, organisms that are sensitive to temperature e.g. phytoplankton, may not be able to survive at higher temperatures, so their numbers decrease. This means that less CO2 is used by them for photosynthesis, so less carbon is removed from the atmosphere
- Warmer water is also less able to absorb CO2 so as temperatures rise, the amount of CO2 that could potentially be dissolved in the sea decreases

Question 7

water and carbon

Answer 7

1. Carbon is a fundamental building block of life — all living things contain carbon
2. Water is also essential for life — all living things need water to survive
3. Water is present in the atmosphere as water vapour, and carbon exists as carbon dioxide and methane. These are greenhouse gases — they cause a natural greenhouse effect that prevents some energy from escaping into space and reflects it back to Earth. This causes temperatures on Earth to be higher than they would otherwise be — without the natural greenhouse effect the Earth would be frozen and uninhabitable
4. Human activities are increasing the concentration of greenhouse gases in the atmosphere. Most scientists agree that this is causing an enhanced greenhouse effect. This is where the additional greenhouse gases reflect more energy back to the Earth than in the natural greenhouse effect, so temperature increases even further

Positive and negative feedback:
Examples of feedbacks in the water cycle:
Positive:
- Temperatures rise - evaporation increases - amount of water vapour in the atmosphere increases - greenhouse effect increases
Negative:
- Temperatures rise - evaporation increases - amount of water vapour in the atmosphere increases, causing more clouds to form - increased cloud cover reflects more of the suns energy back into space - temperatures fall
Examples of feedbacks in the carbon cycle:
Positive:
- Temperatures rise - plant respiration rate increases - amount of CO2 in the atmosphere increases - greenhouse effect increases
Negative:
- CO2 in the atmosphere increases - extra CO2 causes plants to grow - plants remove CO2 from the atmosphere - amount of CO2 in the atmosphere reduces

• In these examples, the positive feedbacks would increase global warming because they’re amplifying the temperature rise. The negative feedbacks would cancel out the temperature increase, so global warming wouldn’t increase

The carbon and water cycles depend on each other:
- Carbon combines with water in the atmosphere. This allows chemical weathering, which removes carbon from the atmosphere
- Water is needed for photosynthesis, which removes carbon from the atmosphere
- The amount of CO2 in the atmosphere affects global temperatures, which affect the amount of evaporation that can take place, which affects the amount of precipitation

Question 8

carbon and climate change

Answer 8

Climate change is predicted to have major impacts on plants, animals and people, for example:

1. The pattern of precipitation is expected to change — wet areas are expected to get wetter and dry areas are expected to get drier. This could cause water shortages in some areas, which could lead to conflicts in the future
2. Extreme weather events (e.g. storms, floods and droughts) are expected to get more frequent. Less developed countries will probably be worst affected as they are less able to deal with the impacts
3. Agricultural productivity will decrease in some areas, which could lead to food shortages
4. Sea levels are expected to rise further. This will flood coastal of low-lying areas
5. Plankton numbers may decline if temperatures increase, which will have a knock-on effect on marine food chains
6. Humans have influenced the carbon cycle for centuries, particularly by extracting and burning fossil fuels.
There is now 40% more CO2 in the atmosphere than there was in 1750
7. The Intergovernmental Panel on Climate Change (IPCC) is an international organisation set up by the UN to share knowledge about climate change. The IPCC states that countries need to reduce the amount of CO2 emitted by human activities in order to prevent large temperature rises. People are trying to mitigate the impacts of climate change by reducing transfers of carbon to the atmosphere
   
These measures can be at a range of scales, for example:
   Individual:
   - People can choose to use their cars less and buy more fuel efficient cars
   - They can also make their homes more energy efficient, e.g. with double glazing, insulation and more efficient appliances

Regional and National:
- Governments can reduce reliance on fossil fuels for heating and powering homes by increasing the availability and reducing the cost of renewable energy sources such as wind, tidal and solar
- Afforestation and restoring degraded forests can increase carbon uptake by the biosphere
- Planners can increase the sustainability of developments by improving public transport and creating more green spaces
- Governments can invest in carbon capture and storage (CCS). CO2 emitted from burning fossil fuels is captured and stored underground e.g. in depleted oil and gas reservoirs

Global:
- Countries can work together to reduce emissions. For example, the Kyoto Protocol (1997) and the Paris Agreement (2015) are international treaties to control the total amount of greenhouse gases released. Participating countries agree to keep their emissions within set limits
- There are also international carbon trading schemes. Countries and businesses are given a limit on the emissions they can produce - if they produce less they can sell the extra credits, if they produce more they need to buy more credits

Question 9

amazon case study

Answer 9

1. The Amazon is the world’s largest tropical rainforest and covers 40% of the South American landmass
2. It has a hot, very wet climate and the vegetation is very dense
3. Many groups of indigenous people live in the Amazon rainforest
4. It’s home to up to 1 million plant species. The Amazon is also home to many endangered species, including the black caiman

Water cycle:
1. The water cycle causes the Amazon to be very wet - there is a lot of evaporation over the Atlantic Ocean, and the wet air is blown towards the Amazon. This contributes to the Amazon’s very high rainfall
2. Warm temperatures mean that evaporation is high in the rainforest itself, which increases the amount of precipitation
3. The rainforest has a dense canopy - this means that interception is high. As a result, less water flows into rivers than might otherwise be expected, and it does so more slowly
4. The water cycle affects the Amazon environment - it is populated by species that are adapted to high humidity and frequent rainfall

Carbon cycle:
1. The Amazon rainforest stores lots of carbon in its vegetation and soil, so it’s a carbon sink
2. The increasing concentration of CO2 in the atmosphere has led to increased productivity in the Amazon rainforest because the vegetation is able to access more CO2 for photosynthesis
3. As a result, the amount of CO2 sequestered by the Amazon rainforest has increased, making it an even more important carbon store
4. However, it has been suggested that although trees are growing more quickly, they’re also dying younger
5. As a result, we may not be able to rely on the Amazon rainforest to continue to be such an effective carbon sink in the future

Human activities affecting the water and carbon store:

Deforestation:
Effects on the water cycle:
1. In deforested areas there is no tree canopy to intercept rainfall, so more water reaches the ground surface. There is too much water to soak into the soil. Instead the water moves to rivers as surface runoff, which increases the risk of flooding
2. Deforestation reduces the rate of evapotranspiration - this means less water vapour reaches the atmosphere, fewer clouds form and rainfall is reduced. This increases the risk of drought

Effects on the carbon cycle:
1. Deforestation means that there is less leaf litter, so humus isn’t formed. The soil cannot support much new growth, which limits the amount of carbon that is absorbed.
2. Trees remove CO2 from the atmosphere and store it, so fewer trees means more atmospheric CO2 which enhances the greenhouse effect and global warming

Climate change:
1. Climate change can severely impact tropical rainforests. In some areas temperature is increasing and rainfall is decreasing, which leads to drought. The Amazon had severe droughts in 2005, 2010 and 2015-16
2. Plants and animals living in tropical rainforests are adapted to moist conditions, so many species die in dry weather. Frequent or long periods of drought could lead to extinction of some species. Drought can also lead to forest fires, which can destroy large areas of forest, releasing lots of CO2 into the atmosphere
3. Scientists predict that a 4 °C temperature rise could kill 85% of the Amazon rainforest. This would result in lots of carbon being released into the atmosphere as the dead material decomposed, and less carbon dioxide being taken in from the air by trees for photosynthesis

Attempts to limit human impacts on the Amazon:
Selective Logging:
1. Only some trees (e.g. just the oldest ones) are felled
2. This is less damaging to the forest than felling all the trees in an area. If only a few trees are taken from each area the forest structure is kept. This means the forest is able to regenerate, so the impact on the carbon and water cycle is small

Replanting:
1. New trees are planted to replace the ones that are cut down. For example, a project in Peru replanted over 115 acres of forest between 2016 and 2019
2. It’s important that the same types of tree are planted that were cut down, so that the local carbon and water cycles return to their initial state

Environmental law:
1. Laws that ban the use of wood from forests that are not managed sustainably
2. Laws that ban excessive logging
3. Laws that control land use e.g. the Brazilian Forest Code says that landowners have to keep 50-80% of their land as forest

Protection:
1. Many countries have set up national parks and nature reserves to protect rainforests. For example, the Central Amazon Conservation Complex in Brazil was set up in 2003 and protects biodiversity in an area of 49,000 km^2 while allowing local people to use the forest in a sustainable way
2. Within national parks and nature reserves, damaging activities such as logging can be monitored and prevented