explain the terrestrial carbon cycle
1) primary producers sequester carbon through photosynthesis which uses gaseous carbon to create carbohydrates with the use of solar energy
2) this process causes carbon fixation which turns gaseous carbon into organic carbon as plants create cellulose
3) producers respire and break down some of the carbohydrates, releasing gaseous carbon back into the atmosphere
4) consumers eat producers and therefore organic carbon, gaseous carbon released back into the atmosphere
5) organisms die and dead organic matter mixes with soils where it is decomposed by decomposers (earthworms), this releases gaseous carbon into the soil
6) some organic carbon may be preserved and converted eventually forming fossil fuels
7) humans burn fossil fuels causing combustion which releases carbon back into the atmosphere
explain the importance of terrestrial ecosystems in terms of sequestration and as a store
- terrestrial plants sequester 100-120Gt of carbon a year
- 95% of a tree’s biomass is made up of the co2 that it sequesters and converts into cellulose
- carbon fixation turns co2 into living organic compounds that grow
- biological carbon can be stored in soils in the form of dead organic matter, the carbon is stored in the humus ( key part of the soil)
stores:
- biomass
- soil
- permafrost
explain the importance of carbon for soil health and how it gets into the soil
how does it get into the soil?
- organic carbon is added to soil when plants and animals die and excrete
- this is broken down by decomposers to produce humus and eventually released as CO2 when broken down
why is it important?
1) helps with permeability and water infiltration- maintains pore spaces, crucial for their longevity, moisture retention
2) organic fertilisers- supplies nutrients to fuel plant growth, cycle of nutrients
3) maintains a strong structure- less likely to be eroded away, less vulnerable of being washed away
soil health is influenced by stored carbon which is important for productivity
explain the role of mangroves as a carbon sink
- they sequester a lot of carbon, almost 1.5 metric tonnes of carbon per hectare every year
- natural form of protection
- underwater gives anaerobic conditions which means the decomposition of matter is slow, so little carbon is respired out into the atmosphere, very slow break down of the plant
- if 2% of mangroves are lost, the amount of carbon released will be 50 times the natural sequestration rate
- considered one of the most vital ecosystems in the world
explain the role of the tundra as a carbon sink
- permafrost stores carbon, permanently frozen ground, dead and decayed organic matter is frozen woking any carbon into an ice store, carbon trapped
- ancient carbon stored in permafrost, the deeper down you go the older the carbon is
- some form of growth, litter goes into top layer of permafrost
- microbes unfreeze as global warming increases, enhances GW
- fear of positive feedback loop where through global warming we will see the thawing of permafrost leading to release of co2 which will lead to further thawing
- active layer deepening with climate change, thaws during summer but depends on the temperature which determines how deep and the amount of co2 that is released
explain the role of tropical rainforests as a carbon sink
- they sequester more co2 than any other terrestrial biome, accounting for 30% of global net primary production (photosynthesis)
- huge carbon sinks but are very fragile and can disappear
- soils are relatively thin and lack nutrients because of fast decomposition
explain the imbalanced nature of carbon
- the carbon cycle was balanced/in equilibrium when the sources of atmospheric carbon are balanced with the sinks (if photosynthesis keeps up its the release of GGs)
- it has become imbalanced since the industrial revolution
what is NPP and give the top 3?
net primary productivity
- it is a measure of the rate of photosynthesis in an ecosystem and therefore gives a measure of the size of the carbon sink
- it is controlled by climate and the availability of nutrients
1) open oceans (ocean acidification, rising temps)
2) tropical rainforests (deforestation, mining and HEP)
3) savannah grassland (conversion to farming)
what are the two carbon pathways as a result of fossil fuel combustion?
1) through rising temps, it may lead to a rise in biodiversity in the arctic therefore becoming a larger carbon sink, short-term balance is reached NEGATIVE FEEDBACK
2) the decomposition of plant material in wet soils reduces carbon stores by releasing co2 and methane. this increases GGs which reinforces global warming in the longer term
POSITIVE FEEDBACK
negative feedback- when a process or event results in a reduction in an effect
positive feedback- when a process or event results in an amplification of an event, e.g permafrost loss, forest loss
what are the impacts of fossil fuel combustion on climate?
- arctic temps are increasing at double the rate (arctic amplification) with a reduction in sea ice, ablation of glacier and reduction in snow cover
- the Sahel and south africa and generally in the tropics will become even dryer, hydrological drought
- extra tropical low pressure systems (depressions) will move northwards
- more extreme general weather
what are the impacts of fossil fuel combustion on the hydro cycle?
- drier mediterranean climate will cause a 20-30% reduction in water availability
- river discharge will reduce from glacier fed rivers as glaciers recede (e.g. the Andes)
- temperate and tropical zones may experience stronger storm activity as a result of more heat and evaporation
- more intense rainfall leads to increase in saturated overland flow and infiltration excess over land flow
what are the impacts of fossil fuel combustion on ecosystems?
- habitats shift poleward or to higher altitudes resulting in biodiversity reducing as some species struggle to migrate
- 10% of land species with limited adaptability will face extinction as habitats change, could reach 40%, polar regions at highest risk
- 80% of coral reefs could be lost through coral bleaching and ocean acidification
- plants attacked by pests, disease and invasive species
explain the factors why future emissions, atmospheric concentration levels and climate warming are uncertain
natural factors
1) the role of carbon sinks
- different sinks have a varying capacity in storing carbon
- we dont know how their exploitation will continue, what rate will deforestation continue?
- will ecosystems be able to adapt? how will GW affect their sequestering ability?
human factors
1) population growth
- if it levels off or not, this significantly affects GG emissions
2) economic growth
- industrial change, shift to a green economy?
- economic growth supporting a shift to renewable tech
3) developments in tech and energy resources
- will innovation allow for affordable renewable energy?
- will fossil fuels be completely replaced?
feedback mechanisms and tipping points
1) permafrost thaw
- to what point will this initiate a positive feedback loop
- how much carbon will be released?
2) forest dieback
- possible passing of tipping points, irreversible alterations to thermohaline circulation
explain tipping points
- it is the point at which a system changes irreversibly (also known as a critical threshold), create ‘runaway climate change’
- it may be reached as a result of positive feedback loops (e.g. permafrost melt)
- e.g. arctic see ice and the albedo effect and forest dieback in the amazon
the positive feedback loop of arctic sea ice is where the ice melts and then the albedo effect will lessen and so the warming of the arctic will be amplified which in turn will lead to further warming
tipping points:
1) permafrost methane
2) ice sheet collapse, melt of Greenland ice sheets
3) amazon dieback
4) Gulf Stream slow down
5) change in ENSO amplified
explain the arctic positive feedback debate
view 1: positive feedback
- through global warming we are seeing a thawing in the permafrost which releases trapped carbon into the atmosphere as co2 and methane and this then lead to further warming due to rise in co2 and methane and this cycle loops
- this is enhanced through the lowering in the albedo effect through the melting of glaciers and so the sun is no longer affected
view 2: negative feedback
- the carbon source below ground with the permafrost melt could be balanced out by the carbon sink above ground of the growing vegetation
- the warming temps may lead to an increase in biodiversity through more suitable temperatures and so this will support more vegetation, thus leading to a higher carbon sink through the rise in biodiversity
what is an energy pathway, explain them and give examples of two pathways?
the route by which energy is transferred from the production area to the consumption area
- there is a mismatch between supply and demand across the world and so his has led to the need for energy pathways, e.g. USA production = 20.5%, consumption = 24.3%
1) ESPO (east Siberia Pacific Ocean)
- a 4188km-long pipeline that exports crude oil from russia to china, South Korea
2) Kazakhstan-China pipeline is 2800km long and transports crude oil from western Kazakhstan to xingjiang, western china
- lots of pathways going away from the Middle East to OPEC
- large pathways from russia to Europe, geopolitical tensions
- very small amounts of oil going to Australia as they still have large reserves of coal
- OPEC is a permanent IGO of 13 oil-exporting developing nations that coordinates and unifies the petroleum policies of its member countries
- 1/2 of the world’s oil is moved by tankers travelling on iced shipping routes
what is a chokepoint?
it is an area in an energy pathway that is prone to disruption
- this can be due to a physical chokepoint which is a narrowing in the sea channel or due to human factors which can cause disruption
- the Suez Canal is a physical chokepoint, it is a physical narrowing of the sea channel which can lead to ships getting stuck
- over half of the world’s oil goes through the 8 major chokepoints
what are the physical and human causes of disruption to energy pathways?
human
- straits of malacca’s piracy, criminal gangs seize ships for hostage payments, over 500 attacks occurred from 2009-15
- geopolitics, Russian gas to europe
- technical problems like pipeline leaks: pipelines must be monitored, e.g. deepwater horizon oil spill
- political reasons, pipelines in Nigeria were bombed in 2016 by militants, resulting in a loss of 300k barrels of crude oil a day
physical
1) extreme weather
- storm in the uk in 2013 damaged important pipelines, gas supplies down for 6hours
2) physical chokepoints
- straits of Malacca 1.7 miles wide at its narrowest
- strait of hormuz, 20% of the world’s oil passes through this, a 39km stretch of water
explain the political cause of disruption: Russian gas to Europe
- tensions with Ukraine and russia through the UK wanting to join the EU
- russia supplies 23% of the EU’s gas
- in 2006 and the winter of 2008-09 they also turned off supplies which led to shortages in Eastern Europe, hardship for citizens during cold winter
- in 2015, the uk agreed to double its imports of Russian gas due to the declining output of the North Sea’s gas fields
- the Ukraine is in a position to make the transfer difficult, e.g. hike prices, stop flows, the UK should stop their reliance on Russian oil, take over the Ukraine
explain the geopolitical case of disruption: syrian conflict
- many argue that the syrian conflict of russia and its Shias vs USA and Sunni is due to their want to control strain territory in order to control European energy
- russia support Assad in the aim to in the future build pipelines
- sunni Qatar and Saudi Arabia also want to build pipelines, they are US allies, explains why the US allow some jihadists to conquer a strip through syria where the US would build pipelines
- europe is the world’s largest energy market and so this has led to this rise in conflict with the hope to take power of this huge market
explain the deepwater horizon oil spill of 2010 (physical difficulties in extraction and accidents)
- gas explosion occurred due to a leak and pressure building up undetected
- unconventional oil supply as difficult to obtain due to deep water (Mississippi canyon) was over 5000m deep into the oil, makes it more prone to accidents
- caused 11 deaths
- supply for US east coast industry disrupted
