The carbon cycle

Question 1

What is a carbon sink?

Answer 1

Anything that absorbs more carbon from the atmosphere than it releases

Question 2

What is a carbon source?

Answer 2

Anything that releases more carbon into the atmosphere than it absorbs

Question 3

What is a carbon flux?

Answer 3

The transfer of carbon between stores

Question 4

Explain the concept of dynamic equilibrium in relation to the carbon cycle

Answer 4

• when sources are equal to sinks and the carbon cycle is in balance
• there is no change in the size of pools over time because inputs and outputs are equal

Question 5

How does the hydrosphere store carbon?

Answer 5

• stored in oceans as dissolved CO2
• stored on the ocean floor as sediment accumulates

Question 6

How does carbon become stored in deep ocean sediments?

Answer 6

• organisms eg. coccoliths die and their shells sink to the bottom of the oceans
• the shells are rich in calcium carbonate and compress into layers of chalk which locks up hydrospheric carbon into the lithosphere

Question 7

What are the stores of carbon in the biosphere?

Answer 7

• animals, plants, soils and microorganisms
• peat - accumulation of partly decayed vegetation
• litter - decaying remains of plants

Question 8

Why is atmospheric CO2 of great importance?

Answer 8

• greenhouse gas which traps heat in the atmosphere so regulates temperatures suitable for humans
• photosynthesis requires CO2, which then provides humans with oxygen to survive

Question 9

How does tectonic uplifting play a role in the carbon cycle?

Answer 9

• tectonic uplifting of carbonate rocks exposes them to the atmosphere
• weathering releases the carbon into oceans where it is taken up by sea creatures to be used in shells
• shells are compressed into calcium carbonate rocks and the cycle begins again

Question 10

What is combustion?

Answer 10

burning of organic materials which releases carbon dioxide

Question 11

What is decomposition?

Answer 11

when organisms die they are consumed by decomposers such as bacteria and fungi. During decomposition, carbon from their bodies is returned to the air as carbon dioxide

Question 12

What are examples of burial and compaction?

Answer 12

• organic material compacted by sediments to form hydrocarbons which are combusted
• corals and shelled organisms convert hydrospheric carbon into calcium carbonate, which compacts when they sink and die, and limestone is formed and carbonates dissolve, releasing CO2

Question 13

What is carbon sequestration?

Answer 13

transfer of carbon to plants, soils, rocks and oceans. Can be through both human and natural processes eg. carbon capture/change in farming practices

Question 14

How does weathering release carbon?

Answer 14

when CO2 is absorbed by rainwater it forms a mildly acidic carbonic acid. Through chemical reactions, rocks slowly dissolve with carbon held in solution, which is transported to oceans and builds up shells of organisms

Question 15

How do animals transfer CO2?

Answer 15

• respiration
• death
• decomposition
• enterric fermentation (cows release methane)
• eating other organisms or plants

Question 16

How can weathering and carbon release lead to succession?

Answer 16

• rock is weathered and broken down by carbonation weathering which releases carbon
• this supports vegetation eg. lichen and moss (pioneer species) to grow which adds organic matter to the soil
• soil becomes less hostile and can support a wider range of plants to establish habitats

Question 17

What are phytoplankton?

Answer 17

organisms which photosynthesize and release CO2 on the top layer of the ocean

Question 18

What are the 8 flows/transfers in the carbon cycle?

Answer 18

• photosynthesis
• respiration
• decomposition
• combustion
• sequestration
• compaction
• weathering
• ocean uptake/loss

Question 19

What are fast and slow carbon cycles (with examples)?

Answer 19

Fast = days/years/decades - the transfer of carbon from store to store occurs very quickly eg. photosynthesis, respiration, combustion etc

Slow = millions of years - the transfer of carbon is extremely slow eg. burial and compaction of marine organisms in ocean sequestration

Question 20

How does water temperature affect carbon uptake?

Answer 20

• when water is cooler, more CO2 is absorbed
• when water is warmer, less CO2 is absorbed

Question 21

What is the oceanic carbon pump?

Answer 21

• CO2 is transported from the ocean surface to ocean depths. If brought to the surface eg. by upwelling, the cold water will warm up and release CO2 to the atmosphere

Question 22

What is a biological carbon pump?

Answer 22

• living organisms in the ocean move carbon from the atmosphere into surface waters, then down into the deeper ocean and eventually into rocks
• this action of organisms moving carbon in one direction is called a biological pump

Question 23

What are the sources of carbon in the oceanic carbon cycle?

Answer 23

• weathered rock forming a weak carbonic acid in solution, which is transported into oceans by transfers
• shelled organisms
• phytoplankton absorbs CO2 through photosynthesis
• diffusion of CO2 from the atmosphere
• respiration through fish and marine organisms

Question 24

What are the impacts of cold conditions on the carbon cycle?

Answer 24

• colder water can absorb more CO2
• chemical weathering is less active
• different forest coverage affects photosynthesis/respiration
• less effective decomposers
• less ocean water - less sediment builds up
• frozen soil stops transfer of carbon

Question 25

What are the impacts of warm conditions on the carbon cycle?

Answer 25

- warmer water can absorb less CO2 - chemical weathering is more active - different forest coverage affects photosynthesis/respiration - more effective decomposers - more ocean water - more sediment builds up - permafrost melts and releases carbon

Question 26

How can orbital change lead to positive feedback in the carbon cycle?

Answer 26

- orbital change leads to variations in the suns radiation that warms up the earth - temperatures rise leading to a surge of release of CO2 - enhanced greenhouse effect traps more heat into the atmosphere - positive feedback warms the Earth

Question 27

Give an example of negative feedback in the carbon cycle

Answer 27

- rising atmospheric carbon - stimulates growth in vegetation - vegetation absorbs more carbon dioxide - regulates atmospheric carbon levels

Question 28

How do volcanic eruptions affect the carbon cycle and Earth's temperature?

Answer 28

- emit between 100-400 million tonnes CO2 per year - humans emit 30 billion tonnes per year - volcanoes release less than 1% CO2 released naturally by volcanoes per year - never caused detectable global warming because the warming effect of emitted CO2 is counteracted by sulphuric dioxide. Sulphuric dioxide is converted into sulphuric acid which form fine droplets and increase reflection of radiation back to space, cooling the Earth's lower atmosphere

Question 29

How do forest fires affect the carbon cycle?

Answer 29

- turn forests from carbon sinks into carbon sources because combustion returns sequestrated CO2 into the atmosphere - every year wildfires burn 3-4 million km^2 of the Earth's land - wildfires in Alaska have released 12% stored carbon back into the atmosphere - fires explain 80% of the changes in carbon stores over the past milenium

Question 30

How do forest fires affect carbon balance in forests?

Answer 30

- forests are huge carbon sinks because their heavy canopy blocks sunlight from reaching the forest floor and decomposing the litter, so carbon is never returned back to the atmosphere - the trees and plants that are planted after a forest fire are often immature and therefore not an immediate carbon sink - the thinner canopy allows more sunlight to peek through so decomposition speeds up, increasing atmospheric carbon - younger forests cannot hold as much carbon as older forests so much of the carbon released from combustion will remain in the atmosphere

Question 31

Why have global CO2 emissions increased so much since the mid 1800's?

Answer 31

- burning fossil fuels - releases 90% anthropogenic CO2 - farming - methane released, ploughed soil releases more CO2 due to more microbial activity - urban growth - land-use change - 10% all CO2 released eg. deforestation - volcanic activity

Question 32

How can CO2 emissions be reduced?

Answer 32

- renewable energy - afforestation - carbon capture - global agreements eg. PCCA

Question 33

How do fossil fuels affect atmospheric carbon?

Answer 33

- more than 900kg CO2 produced for every 1000kg cement - in 2013, fossil fuel production was at 36 billion tonnes, 61% higher than in 1990 - emissions are dominated by China, USA and India (over 50%) - 34 billion tonnes co2 released per year

Question 34

How does farming affect atmospheric carbon?

Answer 34

- cattle in USA emit 5.5 million tonnes methane each year - this accounts for 20% USA's total emissions - ploughed soil inverts soil layers which mixes with the air and increases microbial activity and decomposition - enteric fermentation accounts for 39% all agricultural carbon sources - corn/wheat/rice/soybean crops - methane emitted, production has doubled since 1960's which translates to 1 billion tonnes carbon captured and released - 44% Asia's total emissions in 2011 came from agriculture

Question 35

How does deforestation affect atmospheric carbon?

Answer 35

- accounts for 20% global CO2 emissions because forest becomes a source rather than a sink - not always due to humans eg. wildfires, overgrazing - 13Ha forest cut down every year (size of Greece) - 3% forests lost from 1990-2005 - losing 200km^2 forest each day now - rainforests could vanish 100 years from now at current rate of deforestation

Question 36

How does urban growth affect atmospheric carbon?

Answer 36

- urban areas occupy 2% total land area however account for 97% all anthropogenic carbon release -urban areas grow by 1.3 million people each week - released in energy consumption for transport, industry, domestic use and cement for buildings - cities are responsible for 47% all global carbon emissions

Question 37

Why is atmospheric carbon important?

Answer 37

- carbon cycle affects amount of gases in the atmosphere which can lead to the enhanced greenhouse effect and global warming, consequently wildfires - may affect other aspects of climate eg. storm frequency/intensity - maintains global temperatures

Question 38

Why is carbon on land important?

Answer 38

- energy for fossil fuels - organic matter essential for plant growth and food production - provides fodder for animals - formation and structure of soil and nutrient recycling - photosynthesis - changes may reduce land stores eg. melting permafrost

Question 39

Why is oceanic carbon important?

Answer 39

- converted to calcium carbonate to form shells - consumed by phytoplankton during photosynthesis - producer for food chains - increased CO2 increases ocean acidity - colder oceans absorb more carbon, warmer oceans store less

Question 40

How can the carbon cycle have regional impacts on climate?

Answer 40

- regions with dense vegetation experience high rates of photosynthesis and respiration - this increases humidity and cloud cover, affecting regional temperatures and rainfall - deforested areas will be drier and less humid due to low photosynthesis and respiration - plankton in oceans create DMS, a chemical substance which promotes the formation of clouds - volcanic eruptions lead to a cooling effect

Question 41

What is carbon budget?

Answer 41

- relationship between inputs and outputs - negative budget = more carbon absorbed than emitted

Question 42

What are the impacts of changes to the carbon cycle on land?

Answer 42

- CO2 decrease = photosynthesis decrease - decomposition decreases so nutrients not recycled - melting permafrost - positive feedback - more wildfires - positive feedback

Question 43

What are the impacts of changes to the carbon cycle on oceans?

Answer 43

- increased CO2 = ocean acidification and lower pH because CO2 dissolves in sea water and forms a weak carbonic acid - will affect marine life and phytoplankton - warmer oceans store less CO2 - more CO2 in atmosphere - positive feedback - thermal expansion and sea level rise - coral bleaching - increased storms/changing ocean currents

Question 44

How does increased CO2 lead to positive feedback in the water and carbon cycle?

Answer 44

- global temperature rise warms oceans - permafrost melts and releases CO2 - water evaporates from ocean surface and dissolved CO2 is released by oceans - more atmospheric CO2 and water vapour leads to enhanced greenhouse effect and positive feedback

Question 45

What is a negative feedback loop in the carbon cycle?

Answer 45

- higher temperatures increase growing seasons for plants, which increases absorption of carbon from the atmosphere - higher temperatures increase phytoplankton that release DMS, a chemical which promotes cloud formation - cloud prevents sunlight from reaching the ground so temperatures decrease, however this also decreases the amount of phytoplankton as photosynthesis will stop

Question 46

What is the relationship between the water and carbon cycle?

Answer 46

- rivers can transport dissolved carbon into oceans - higher air temperatures affect the air's ability to absorb moisture which can shift rainfall patterns leading to droughts - increased CO2 = increased transpiration = heavier rainfall - increased CO2 = melting permafrost - warmer oceans = less dissolved CO2 - higher temp = baked soil = less infiltration

Question 47

What are the strategies used to reduce carbon emissions?

Answer 47

- changing industrial combustion by using renewable energy resources - between 40-50% UK's total energy per day comes from renewable resources (mainly wind) - carbon capture and storage - can catch 90% of emissions, which would cut global carbon emissions by 19% - transport schemes - ULEZ, congestion charge, park and ride scheme - changing land use - grasslands can sequester approx 810 million tonnes CO2 globally (avoiding overgrazing, organic rather than artificial fertilisers, reduce ploughing) and peatlands are made from around 50% carbon so are a large carbon sink (restoration of peatlands)

Question 48

What is the debt for nature swap?

Answer 48

in 2010, USA converted $13.5 million of debt from Brazil into a fund to support the protection of the rainforest

Question 49

What is the Paris 2015 climate convention?

Answer 49

- 195 countries agreed to reduce global CO2 emissions to below 60% of 2010 levels by 2050 - global temperature increase is limited to increase to 1.5 degrees above pre-industrial levels

Question 50

What is the issue with large global agreements about climate change?

Answer 50

- HICs have developed using fossil fuels so LICs argue that they should have the opportunity to be able to develop - if richer countries eg. USA pull out, the whole agreement is at risk because they are huge emitters - it is easier for HICs to implement strategies to combat climate change, harder for LICs