44 terms

A2 Geography: Carbon and Energy Security EQ1

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What is the Carbon cycle?
the biogeochemical cycle by which carbon moves from one sphere to another. It acts as a closed system made up of linked subsystems that have inputs, throughputs and outputs. Carbon stores function as sources (adding carbon to the atmosphere) and sinks (removing carbon from the atmosphere)
What are the stores carbon is present in?
- atmosphere as CO₂ and methane

-hydrosphere as dissolved CO₂

-lithosphere as carbonates in limestone and fossil fuels such as coal, oil and gas

-biosphere in living and dead organisms
What are fluxes?
movements of organic compounds through an ecosystem
What are petagrams (Pg) or gigatonnes (Gt)?
the units used to measure carbon; one petagram/ gigatonne is equal to a trillion kilograms or 1 billion tonnes
What is reservoir turnover?
the rate at which carbon enters and leaves a store is measured by the mass of carbon in any store divided by the exchange flux
What is sequestering?
the natural storage of carbon by physical biological processes such as photosynthesis
What are the different carbon stores in order of size?
long term stores
-crustal geological: sedimentary rocks

-oceanic (deep): dissolved inorganic carbon

short term stores
-terrestrial soil: plant biomass and microorganisms

-oceanic (surface): dissolved carbon and plankton

-atmospheric: CO₂ and CH₄ as greenhouse gas stores

-terrestrial ecosystems: CO₂ is taken from the atmosphere by plant photosynthesis
What are processes?
the physical mechanisms that drive the flux of material between stores
What are the key processes in the geological carbon cycle?
-weathering: breakdown of rocks

-decomposition: particles that result from decomposition after death store carbon

-transportation: transportation rivers carry particles to oceans

-sedimentation: over millennia these sediments accumulate and bury others eg. limestone

-metamorphosis: layering of sediment creating rocks
How are oil and natural gas formed?
-from tiny aquatic animal+plant remains

-occur in pockets in rocks, migrating up through the crust until meeting caprocks

-natural gas eg. methane is made up of fractions of oil molecules, smaller so with a lower boiling point

-other deposits are oil shales, tar sands and gas hydrates
How is coal formed?
-from remains of trees, ferns and other plants

-there are four types of coal:
=anthracite, hard with the most carbon and hence most energy
=bituminous coals, next in hardness+carbon content
=soft coals eg. brown and lignite only have 25% and emit more CO₂
=peat, stage before coal, important energy source
What are the five phases of the geological carbon cycle?
1. chemical weathering: in the atmosphere, water reacts with atmospheric CO₂ and carbonic acid forms. this dissolves surface minerals

2. transportation of calcium ions by rivers. these combine with bicarbonate ions to form calcium carbonate

3. deposition turns this into limestone

4. subduction of the sea floor under continental margins

5. some of the carbon rises within magma and is degassed as CO₂ and returns to the atmosphere
Where does outgassing occur?
-active or passive volcanic zones associated with tectonic plate boundaries, including subduction zones and spreading ridges

-places with no current volcanic activity, such as hot springs and geysers at Yellowstone

-direct emissions from fractures in the Earth's crust
How significant is volcanic outgassing?
volcanos emit 0.15 - 0.26 Gt CO₂ annually compared to human 35Gt from fossil fuels etc, so relatively insignificant
What is the negative feedback loop regulating the geological carbon cycle?
Increase in volcanic activity

Rise in CO₂ emission and loss of carbon from rocks

temperature rises

more uplift of air, condensation and rain

more chemical weathering and erosion of rocks

more ions deposited on ocean floors

more carbon stored in rocks

more volcanic activity
What is oceanic sequestration?
carbon enters the oceans through river run off and dissolving and some enters long term stores in ocean sediment with fluxes operating in millennia
What is a carbon cycle pump?
processes operating in oceans to circulate and store carbon. these are three sorts: biological, carbonate and physical.
What is thermohaline circulation?
the global system of surface and deep water ocean currents is driven by temperature (thermo) and salinity (haline) differences between areas of oceans
What are the features of oceanic biological pumps?
sequestration by phytoplankton, single celled marine plants that float near the oceans surface. They use the carbon to photosynthesise. 0.1% of the carbon they use reaches the sea floor when the dead phytoplankton die and sink.
What are the features of oceanic carbonate pumps?
relies on inorganic carbon sedimentation. CaCO₃ from shells and skeletons dissolve when they die or reach the sea floor as sediments. the dissolved CaCO₃ becomes part of deep ocean currents. Shells that dont dissolve build up eg. white cliffs of dover
What are the features of physical ocean pumps?
based on oceanic circulation of water including upwelling, downwelling and the thermohaline current. CO₂ is released in warm tropical waters but held dissolved in colder waters. At colder higher latitude areas, water also gets colder and more dense and sinks, taking carbon down with it.
What are the stages of thermohaline circulation?
1. main current begins in polar oceans where the water gets very cold; sea ice forms; surround sea water gets saltier, increases in density and sinks

2. the current is recharged as it passes through Antarctica by extra cold salty, dense water.

3.division of main current: northward into the Indian Ocean and into the western Pacific.

4. the two branches warm and rise as they travel northward, then loop southward and westward

5. now warmed water continue circulating the globe and return to the north Atlantic and cool and the cycle begins again
What are the aspects of terrestrial sequestration?
-primary producers - plants - take carbon out of the atmosphere through photosynthesis and release CO₂ back into the atmosphere through respiration

-when consumer animals eat plants, carbon from the plant becomes part of its fats and proteins

-micro organisms and detritus feeders eg. beetles feed on animal waste, and this becomes part of the microorganisms

-after plant and animal death, the tissues decompose. this happens fastest in hot climates, however carbon can be locked in tissues for years in cold climates
How do carbon fluxes vary?
-diurnally: during the day the fluxes are positive, from the atmosphere to the ecosystem; at night the flux is negative, with loss from the ecosystem to the atmosphere

-seasonally: in the northern hemisphere winter, when few land plants are growing and many are decaying, atmospheric CO₂ conc. rise; during the spring when plants grow again concs. drop
How can carbon sinks be affected anthropogenically?
can be changed into carbon sources, eg. in forest burning
How are tropical rainforests involved in the carbon cycle?
one of the largest organic stores of carbon

Amazon rainforest sequesters 17% of all terrestrial carbon.
How are wetlands involved in the carbon cycle?
contain peat formed in the holocene that is an important carbon store
How much carbon does soil store?
20-30per cent of global carbon
What is the capacity of soil to store organic carbon determined by?
-climate: controls plant growth and microbial and detritivore activity. rapid decomposition at high temperatures or in waterlogged conditions

-soil type: clay rich soils have higher carbon content than sandy soils, clay protects carbon from decomposition

-management and use of soils: since 1850 soils have lost 40-90 billion tonnes (Gt) of carbon through cultivation and disturbance. current loss due to land use change
How is the earths climate driven by shortwave solar radiation?
-approx. 31% is reflected by clouds, aerosols and gases in the atmosphere and land surface

-remaining 69% is absorbed, 50% by earths surface, especially by oceans

-69% of this surface absorption is re-radiated to space as longwave radiation

-however a large proportion of this long wave radiation emitted by the surface is re-radiated back to the surface by clouds and greenhouse gases; this trapping of longwave radiation in the atmosphere is what gives 15°C to support life
What is the Anthropocene?
the name that is often given to the current geological era of the Holocene due to the profound changed made by humans. the natural greenhouse effect has become enhanced; CO₂ has increased in volume by 40% in the last 300 years
Where does highest photosynthesis occur?
-on land: in areas that are warm and wet. amount of water limits primary production. eg. deserts have little biomass above ground. forests store the largest amount of carbon. tundra has highest density of carbon storage in the permafrost

-in oceans: in shallower water, allowing higher photosynthesis, and in places receiving high nutrient inputs
What is CO2 fertilisation?
rises in CO₂ speeding up the rate of photosynthesis and hence Net primary productivity (NPP) by 63% by 2100. however plant growth is limited by nutrient availability and as a result IPCC estimates extra growth of only 20%
What is the MEA?
Millennium Ecosystem Assessment, the UN MEA was the first major global audit of the health of ecosystems in 2005, highlighting their degradation (loss of natural productivity through overuse and destruction)
What does soil health depend on?
the amount of organic carbon stored in the soil, depending on imputs (plant and animal residues and nutrients) and outputs (decomposition, erosion and use in plant and animal productivity)
What does carbon give soil?
its water retention capacity, its structure and its fertility
What does the IPCC model for carbon suggest?
-increased fluxes to the biological store

-increased soil storage in high latitudes, only limited by nitrogen availability

-loss of storage in unfreezing permafrost and in the Southern Ocean and North Atlantic because of warming
What is climate forcing?
means the causes, or drivers, of climate change. Currently the most important driver is fossil fuel combustion.
What are the global climate predictions?
on average, the Earth will become warmer, hence more evaporation and precipitation

sudden shifts in weather patterns

more extreme intense and frequent events

rising mean sea level
What are the regional climate change predictions?
some regions will become warmer and drier, others wetter

some regions will have less snow more rain

storm surges may increase
What is positive feedback?
global warming creates ice melt, and permafrost thawing releases trapped methane. Drying forests and warming oceans emit CO₂. Increased greenhouse gases mean increased warming
How are marine organisms threatened by increased CO2 levels|?
progressively lower oxygen levels and high rates and magnitudes of ocean acidification as well as rising temperatures which may alter the food chain due to plankton growth
What are the implications of increased CO2 levels on the hydrological cycle?
-increased evaporation rates and hence trigger more moisture circulating through the cycle, rater than storing in oceans, and intense precipitation events

-change in precipitation types, as in northern hemisphere where spring snow cover has decreased in extent; earlier springs mean earlier peaks in snowmelt and resulting river flows and into ocean stores

-increased surface permafrost temperatures, a trend recorded since the early 1980s

-reduce sea ice, ice cap and glacier storage, as in the Arctic already

-change in the capacity of terrestrial ecosystems to sequester carbon and store water; eg. importance of storage in the Amazon where 60% evaporation originates from EVT by upwind ecosystems
How is ENSO affected by increased carbon?
El nino-Southern Oscillation is an important factor in the Earths climate system and affects hydrological cycle. Droughts and floods driven by ENSO may be more intense and increase in frequency with warming atmosphere and oceans

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