1.1.3 The Carbon Cycle (global)

Question 1

Carbon Sink

Answer 1

any store which takes in more carbon than it emits e.g. intact/virgin tropical rainforest

Question 2

Carbon source

Answer 2

any store that emits more carbon than it stores e.g. a damaged tropical rainforest

Question 3

Main carbon stores (in order of magnitude)

Answer 3

1 Marine sediments and sedimentary rocks
2 Oceans
3 Fossil Fuel Deposits Soil Organic Matter
4 Atmosphere
5 Terrestrial Plants

Question 4

Marine Sediments and Sedimentary Rocks

Answer 4

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.

Question 5

Oceans

Answer 5

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.

Question 6

Fossil Fuel Deposits

Answer 6

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.

Question 7

Soil Organic Matter

Answer 7

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.

Question 8

Atmosphere

Answer 8

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.

Question 9

Terrestrial Plants

Answer 9

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.

Question 10

Which sphere is the main store of carbon?

Answer 10

Lithosphere.

Question 11

How are the stores distributed?

Answer 11

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.

Question 12

How are forests changing?

Answer 12

Declining in tropical areas in S hemisphere. Growing in N hemisphere.

Question 13

Non-tropical forests…

Answer 13

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.

Question 14

Forests in industrialised regions…

Answer 14

are expected to increase by 2050 but in the global

south, forested areas will decrease.

Question 15

Rate of forest loss…

Answer 15

has decreased

Question 16

The eight countries with the largest forested areas are:

Answer 16

Russia, Brazil, China, Canada, USA, DRC, Australia and Indonesia.

Question 17

Most carbon stored on land is…

Answer 17

Brazil (also most extensive deforested area)

Question 18

Larges amount of afforested area

Answer 18

China

Question 19

Net Primary Productivity (NPP)

Answer 19

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.

Question 20

Natural Processes that change the carbon cycle

Answer 20

Wildfires

Volcanic Activity

Question 21

Wildfires

Answer 21

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?

Question 22

Volcanic activity

Answer 22

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.

Question 23

Human impacts on the carbon cycle

Answer 23

Fossil fuel use
Deforestation
Farming practices

Question 24

Fossil Fuel Use

Answer 24

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.

Question 25

Deforestation

Answer 25

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.

Question 26

Farming Practices

Answer 26

Arable farming releases CO₂ as animals respire.

Ploughing can release CO₂ stored in the soil. Farm machinery such as tractors may release CO₂.

Question 27

Fluxes

Answer 27

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.

Question 28

The Carbon Budget

Answer 28

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