2.1.10 Feedback within and between the carbon and water cycles

What is a carbon store

A reservoir where carbon is held for varying lengths of time

What is a carbon sink

A store that absorbs more carbon than it releases

What is a carbon source

A store that releases more carbon than it absorbs

What biome stores the most carbon overall

Tropical rainforests

How much carbon does the Amazon rainforest store

About 100–120 billion tonnes

Where is most carbon stored in tropical rainforests

Above-ground biomass in trees

Why is decomposition rapid in tropical rainforests

High temperatures and humidity

How does high temperature affect carbon storage in rainforests

Increases photosynthesis but also respiration and decomposition

How does high rainfall affect rainforest carbon storage

Supports year-round photosynthesis and high biomass

How does light availability affect rainforest productivity

Constant high solar radiation increases GPP

What biome stores most carbon below ground

Temperate grasslands

How much carbon do temperate grasslands store per hectare

Around 100–200 tonnes

Why do grasslands store most carbon in soils

Extensive root systems and slow winter decomposition

How does seasonal temperature affect grassland carbon storage

Limits decomposition in winter allowing soil carbon accumulation

How does precipitation limit biomass in temperate grasslands

Moderate rainfall supports grasses but not trees

Why is above-ground biomass lower in grasslands than forests

Lack of sufficient rainfall for tree growth

What are peatlands

Waterlogged ecosystems that accumulate partially decomposed organic matter

Why are peatlands important carbon stores

Slow decomposition locks carbon away for millennia

How much carbon do peatlands store globally

Around 550 gigatonnes

Why does peat form slowly

Anaerobic waterlogged conditions reduce decomposition

What happens to peat carbon when drained

Oxidation releases CO₂ and methane

How does peat extraction affect carbon stores

Physically removes long-term stored carbon

How can peatlands shift from sinks to sources

Drainage and drying increase decomposition

What is re-wetting in peatland management

Raising the water table to restore anaerobic conditions

How does re-wetting reduce emissions

Slows decomposition and peat oxidation

What role does sphagnum moss play in peat formation

Promotes peat accumulation and carbon sequestration

Why did Exmoor peatlands become carbon sources

Drainage for agriculture and grouse moor management

How has restoration changed Exmoor carbon balance

Blocking ditches reduced CO₂ emissions and restarted sequestration

What is deforestation

Permanent removal of forest cover

How much deforestation is caused by cattle ranching in the Amazon

Around 60–70%

How does deforestation affect carbon stores

Releases stored carbon and reduces future uptake

What is savannisation

Conversion of rainforest into savanna-like vegetation

How does deforestation reduce rainfall in the Amazon

Reduced evapotranspiration lowers atmospheric moisture

Why does savannisation reduce carbon storage

Savannas store far less biomass than rainforests

How does agriculture reduce soil carbon in prairies

Ploughing accelerates decomposition and erosion

How much soil carbon has been lost from prairies

Around 30–50% of original stores

Why is soil carbon loss long-term

Slow recovery due to shallow-rooted crops

What links the water and carbon cycles

Processes like photosynthesis

Why is water essential for carbon uptake

Photosynthesis requires water

How does transpiration affect the carbon cycle

Maintains plant growth and carbon uptake

How does climate change alter precipitation patterns

Increases rainfall intensity and drought frequency

How does warming increase atmospheric CO₂ indirectly

Accelerates soil respiration and decomposition

What is a positive feedback loop

A change that amplifies itself

What is a negative feedback loop

A process that dampens change

What is the ice-albedo feedback

Melting ice lowers reflectivity and increases warming

Why is permafrost a carbon threat

Thaw releases CO₂ and methane

Why is methane a powerful greenhouse gas

It traps more heat than CO₂

How does Arctic warming affect vegetation

Shrub expansion increases heat absorption

How does ocean warming affect carbon storage

Reduces CO₂ solubility and uptake

What causes ocean acidification

Absorption of atmospheric CO₂

Why is ocean acidification harmful

Reduces carbonate availability for marine organisms

How does sea level rise link to carbon cycles

Warming causes thermal expansion and ice melt

What is thermohaline circulation

Global ocean circulation driven by temperature and salinity

How could melting ice disrupt ocean circulation

Freshwater input reduces sinking of cold saline water

Why are feedbacks important in climate systems

They can accelerate or stabilise climate change

Why is Arctic change globally significant

Feedbacks amplify warming beyond the region