Summary
Summary AQA Physical Geography- Water and Carbon 4 MARKERS
- Module
- Physical geography
- Institution
- AQA
Complete practice of Water and Carbon 4 markers for AQA physical geography A-Level.
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UNIT CRITERIAWater and carbon cycles as natural systems
Systems in physical geography: systems concepts and their application to the water and carbon cycles inputs –
outputs, energy, stores/components, flows/transfers, positive feedback, negative feedback, dynamic equilibrium.
The carbon cycle
Global distribution, and size of major stores of carbon – lithosphere, hydrosphere, cryosphere, biosphere,
atmosphere.
Factors driving change in the magnitude of these stores over time and space, including flows and transfers at
plant, sere and continental scales. Photosynthesis, respiration, decomposition, combustion, carbon
sequestration in oceans and sediments, weathering.
Changes in the carbon cycle over time, to include natural variation (including wild fires, volcanic activity) and
human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use
changes).
The carbon budget and the impact of the carbon cycle upon land, ocean and atmosphere, including global climate
Water, carbon, climate and life on Earth
The key role of the carbon and water stores and cycles in supporting life on Earth with particular reference to
climate. The relationship between the water cycle and carbon cycle in the atmosphere. The role of feedbacks
within and between cycles and their link to climate change and implications for life on Earth.
Human interventions in the carbon cycle designed to influence carbon transfers and mitigate the impacts of
climate change.
Case studies
Case study of the Amazon tropical rainforest to illustrate and analyse key themes in water and carbon cycles and
their relationship to environmental change and human activity.
4-mark questions:
Water and carbon cycles as natural systems
Outline the role of dynamic equilibrium in the carbon cycle
Within the carbon cycle, dynamic equilibrium is the concept of balance between the inputs and outputs in a
system. If the equilibrium is changed, the system attempts to return it to its original state in by opposing the
change. When the change is nullified and returns to its original state, this is the concept of negative
feedback. However, when the change is exacerbated and driven further away from the balanced state of
equilibrium, this is known as positive feedback.
Explain the concept of feedback loops in relation to the carbon cycle
Feedback loops are a series of events triggered by an initial change. Within the carbon cycle, human
activity can cause positive feedback whereby the change in the cycle is exacerbated. For example, when
trees are deforested, this leads to less carbon sequestration and more atmospheric CO2, this results in
increased atmospheric temperatures. An increase in atmospheric temperature can result in an increase in
wildfire activity which in turn leads to further deforestation, exacerbating the original change. Negative
feedback loops however, counteract the original change and reverse its impacts, meaning that the system
reverts back to dynamic equilibrium.
Explain the concept of positive feedback loops in relation to the carbon cycle
Positive feedback is the process whereby an original change causes an exacerbation of change within a
system, amplifying the initial change. Within the carbon cycle, human activity can cause positive feedback
whereby the change in the cycle is exacerbated. For example, when trees are deforested, this leads to less
carbon sequestration and more atmospheric CO2, this results in increased atmospheric temperatures. An
increase in atmospheric temperature can result in an increase in wildfire activity which in turn leads to
further deforestation, exacerbating the original change.
, Explain the concept of negative feedback loops in relation to the carbon cycle
Negative feedback is the process whereby the original change is diminished and the change is reverted
back to a steady state of dynamic equilibrium. For example, within the carbon cycle when the surface
temperature increases slightly due to increased atmospheric CO2, the increased evaporation results in
more cloud cover which then reflects more sunlight back into space and reduces atmospheric
temperatures, nullifying the original change.
The carbon cycle
Outline factors driving change in magnitude of carbon stores
Carbon moves from one store to another in a continuous cycle. Photosynthesis, combustion and
sequestration are the main factors driving change in the magnitude of carbon stores. Photosynthesis is the
process whereby carbon is sequestered by plants, converting CO2 and H2O into carbohydrates and O2.
Combustion is the process of burning fossil fuels, whereby carbon is released from either the biosphere or
lithosphere into the atmosphere.
Explain the role of Cryospheric change in the carbon cycle
The cryosphere is the frozen and tundra regions that contain vast amounts of organic carbon within and
just above the permafrost layer, the cryosphere contains around 2.5 times the amount of carbon the
atmosphere holds. Over time and temperature dependent the role of the cryosphere can change in the
carbon cycle. In a period of global cooling, the cryosphere store grows in size as more regions of the earth
become frozen, locking in vegetation and significantly reducing decomposition. However, in a period of
global warming, the cryosphere store will be reduced. When permafrost melts, the carbon held in the
cryosphere store will be released and transferred into the atmospheric store.
Explain the role of the lithosphere in the carbon cycle
The lithosphere includes the crust and uppermost mantle, carbon is stored in the mantle in both organic
and inorganic form. Most of the carbon stored on earth is held in the lithosphere. Over 99.9% of the earths
carbon is stored in sedimentary rocks such as limestone and about 0.004% of the Earth’s carbon is stored
in the lithosphere in fossil fuels such as coal and oil. The lithosphere holds over 100,000 gigatonnes of
carbon and is earths biggest carbon store.
Explain the role of the hydrosphere in the carbon cycle
The hydrosphere relates to the carbon stored within the oceans and lakes on earth. The ocean plays an
important role in the carbon cycle, the hydrosphere holds around 37,000-40,000 gigatonnes of carbon.
Carbon is found in the hydrosphere dissolved into oceans and lakes. The carbon within this store is often
used by animals to make their shells. For example, as carbon is dissolved into the ocean it is used by
phytoplankton to make their shells. Over time, as phytoplankton dies and sinks to the ocean floor, they are
compacted and cemented into sedimentary rocks.
Explain the role of the biosphere in the carbon cycle
The biosphere is defined as the total sum of all living matter within the carbon cycle; plants and animals.
19% of all carbon stored in the Earth’s biosphere is stored in plants. For example, forests play a significant
role in the carbon cycle and sequester a large amount of atmospheric carbon. For example, the Amazon
rainforest has about 300 billion trees and sequesters around 20% of the worlds ‘forest carbon’. Animals
play a small role in the storage of carbon. However, they are very important in the generation of movement
of carbon through the cycle. When they respire, carbon is transferred to the atmospheric store.
Explain the role of the atmosphere in the carbon cycle
The atmosphere is the smallest carbon store on Earth, holding around 800 gigatonnes of carbon. The
atmosphere plays a significant role in the transfer of carbon as the majority of the carbon is moved through
the atmospheric store. The increased amount of carbon in the atmospheric store has resulted in an
increase in global temperatures, largely due to the emissions released via anthropogenic processes. In
recent years, the carbon stored in the atmosphere is higher than it has been for the past 800,000 years.
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