1.1.3 The Carbon Cycle (global) Flashcards
Carbon Sink
any store which takes in more carbon than it emits e.g. intact/virgin tropical rainforest
Carbon source
any store that emits more carbon than it stores e.g. a damaged tropical rainforest
Main carbon stores (in order of magnitude)
1 Marine sediments and sedimentary rocks 2 Oceans 3 Fossil Fuel Deposits Soil Organic Matter 4 Atmosphere 5 Terrestrial Plants
Marine Sediments and Sedimentary Rocks
Lithosphere - Long-term
Easily the biggest store. 66 - 100 x10^18 metric tons of carbon. The rock cycle and continental drift recycle the rock over time, but this may take millions of years.
Oceans
Hydrosphere - Dynamic
The second biggest store contains a tiny fraction of the carbon of the largest store. 38 x10^12 metric tons of carbon. The carbon is constantly being utilised by
marine organisms, lost as an output to the lithosphere, or gains as an input from rivers and erosion.
Fossil Fuel Deposits
Lithosphere - Long-term but currently dynamic
Fossil fuel deposits used to be rarely changing over short periods of time, but humans have developed technology to exploit them rapidly, though 4 x10^12
metric tons of carbon remain as fossil fuels.
Soil Organic Matter
Lithosphere - Mid-term
The soil can store carbon for over a hundred years, but deforestation, agriculture and land use change are affecting this store. 1.5 x10^18 metric tons of carbon
stored.
Atmosphere
Dynamic
Human activity has caused CO₂ levels in the atmosphere to increase by around 40% since the industrial revolution, causing unprecedented change to the global climate. 0.75 x10^18 metric tons of carbon stored.
Terrestrial Plants
Biosphere - Mid-term but very dynamic
Vulnerable to climate change and deforestation and as a result carbon storage in forests is declining annually in some areas of the world. 0.56 x10^18 metric tons of
carbon.
Which sphere is the main store of carbon?
Lithosphere.
How are the stores distributed?
Unevenly. Oceans are larger in S hemisphere and biosphere storage mostly occurs on land. Terrestrial plant storage is focussed in the tropics and N hemisphere.
How are forests changing?
Declining in tropical areas in S hemisphere. Growing in N hemisphere.
Non-tropical forests…
have seen an increase in carbon sequestration in recent years, especially in Europe and Eastern Asia, due to conversion of agricultural land and plantations to new forests.
Forests in industrialised regions…
are expected to increase by 2050 but in the global
south, forested areas will decrease.
Rate of forest loss…
has decreased
The eight countries with the largest forested areas are:
Russia, Brazil, China, Canada, USA, DRC, Australia and Indonesia.
Most carbon stored on land is…
Brazil (also most extensive deforested area)
Larges amount of afforested area
China
Net Primary Productivity (NPP)
refers to the amount of carbon absorbed by forests. For
tropical forests it is positive all year round, but deciduous forests, have a negative NPP in winter, but across the whole year their NPP is positive.
Natural Processes that change the carbon cycle
Wildfires
Volcanic Activity
Wildfires
Transfer carbon from biosphere to atmosphere as CO₂ is released through burning. This burning can encourage the growth of plants in the long term. There is much debate about whether preventing wildfires is beneficial. They have an important role in the carbon cycle, but
may threaten homes. Is it right to extinguish the ones caused by human activity, or should we extinguish them because global warming is providing better conditions for wildfires to occur?
Volcanic activity
Carbon stored within the earth is released during volcanic eruptions, mainly as CO₂ gas. They contribute a relatively low proportion of CO₂ to the overall carbon cycle.
sulphur dioxide gas produced blocks radiation from the sun and lowers global temperatures. In this way volcanoes can influence the carbon cycle by reducing photosynthesis rates, which will then also affect the water cycle.
Human impacts on the carbon cycle
Fossil fuel use
Deforestation
Farming practices
Fossil Fuel Use
Combustion transfers CO₂ to the atmosphere from a long-term carbon sink. Nearly everything that we do impacts the carbon cycle in one way or another, from buying a new pair of jeans, to switching the light on or getting a drink of water.
Deforestation
Often used to clear land for farming/housing, rapidly releases carbon stored in plants using slash and burn techniques and interrupting the forest carbon cycle.
Farming Practices
Arable farming releases CO₂ as animals respire.
Ploughing can release CO₂ stored in the soil. Farm machinery such as tractors may release CO₂.
Fluxes
Changes to the magnitude of carbon stores over time. May happen very rapidly or over thousands of years. Human activity is causing an unprecedented flux in the levels of CO₂ in the atmosphere as a direct result of fossil fuel combustion.
The Carbon Budget
the balance between carbon inputs and outputs to a store at any scale or the balance of exchanges between the four major stores of carbon:
E.g. The carbon budget in the atmosphere has inputs from respiration and combustion, but outputs including the oceans/photosynthesis
