The Carbon Cycle

Anthropogenic CO2

CO2 generated by human activity

Carbon sink

A store of carbon that absorbs more carbon than it releases

Weathering

The breakdown of rocks in situ by a combination of weather, plants, and animals

Earth’s interior

The primary source of CO2, some naturally escapes at constructive and destructive plate boundaries

IPCC (Intergovernmental Panel on Climate Change)

Provides the main measurements of global carbon levels in gigatonnes carbon equivalent (GtC) to measure the stores and transfers of global carbon

Lithosphere

The hard outer layer of the Earth made up of the crust and uppermost mantle

Inorganic carbon deposits

Lithosphere carbon stores involving fossil fuels and carbonate based sedimentary deposits such as limestone

Organic carbon deposits

Lithosphere carbon stores involving litter (dead organic matter) and humic substances

Twilight zone (Intermediate and deep layers)

Where the vast majority of oceanic (hydrosphere) carbon is stored

Surface layer

Where some oceanic (hydrosphere) carbon is stored by marine organisms that use sunlight to photosynthesise

Ocean biological carbon pump

When photosynthesis by marine organisms such as phytoplankton in surface waters absorbs CO2 and eventually become dead organisms that sink to the ocean floor, where they decay and accumulate in layers of dead marine organisms forming layers of carbon rich sediment which can be locked up for millions of years

19

Percentage of biospheric carbon stored in living vegetation

Plant litter

Fresh, undecomposed, and easily recognisable (by species/type) plant debris - biospheric store of carbon

Soil humus

Thick brown/black substance that remains after most organic litter has decomposed - stable final product of decomposition - biospheric carbon store

Soil

2nd largest global store of carbon behind the ocean, stores more than vegetation etc.

Peat

An accumulation of partially decayed vegetation or organic matter that is unique to peatlands/mires formed in wetland conditions where almost permanent water saturation obstructs flow of oxygen into the ground creating anaerobic conditions that slow down rates of plant litter decomposition - biospheric carbon store

Animals

Play a very small role in the storage of carbon, yet a crucial role in the generation of movement of carbon throughout the carbon cycle

0.04

Percentage of the atmosphere made up of CO2

Net carbon source

A store of carbon that releases more carbon than it absorbs

Geological component

Where the carbon cycle interacts with the rock cycle in the processes of weathering, burial, subduction, and volcanic eruptions - naturally controls atmospheric CO2 levels over hundreds of millions of years

Subduction (geological component of carbon cycle)

Causes carbonaceous sea floor deposits to be pushed deep into the Earth and melt, sending CO2 back towards the surface through volcanic eruptions, seeps, vents, or CO2 rich hot springs, and eventually back into the atmosphere

Weathering (geological component of carbon cycle)

CO2 is naturally removed from the atmosphere by mixing with precipitation to form carbonic acid which upon impacting the surface chemically weathers minerals and carries them through surface streams eventually to the deep ocean

Respiration

When plants that carry out photosynthesis break down organic matter (glucose) which uses O2 and produces CO2 as a by-product. Has the opposite impact on atmospheric CO2 to photosynthesis

Physical mechanisms of decomposition

Animals, wind, or other plants causing fragmentation or leaching of dead organisms

Chemical mechanisms of decomposition

Uses oxidisation and condensation to break down dead organisms

Decomposition

The breakdown of dead organic matter which returns nutrients to the ecosystem and releases stored carbon into the atmosphere, soil, and water, primarily in the form of CO2 or methane

Negative correlation

Relationship between temperature of oceans and amount of CO2 they can store

Vertical deep mixing

When warm ocean water is carried from tropics to polar regions where it is cooled and condensed to sink below the surface layer

Carbon pump

Impact of vertical deep mixing on the ocean through constantly replenishing the surface layer, enabling constant absorption of atmospheric CO2

Combustion

When any organic material is burned in the presence of oxygen to emit CO2 among other products

Biomass combustion

The burning of living and dead vegetation

USGS

Organisation that stated that ‘the CO2 released in recent volcanic eruptions has never caused detectable global warming of the atmosphere’

Sulphur dioxide

Emitted during volcanic eruptions and has an opposite effect to CO2’s greenhouse effect, cancelling out any potential for global warming from increased atmospheric CO2 from the eruption

Sulphuric acid

What sulphur dioxide converts to in the atmosphere after volcanic eruptions. Reflects sun radiation back to space, counteracting the enhanced greenhouse effect

1%

Amount of CO2 released by recent volcanic eruptions compared to that of anthropogenic CO2 emissions in the same time period

Fossil fuels

Formed through the burial of dead plants/animals under multiple layers of sediment creating an anoxic environment that allows for anaerobic decomposition, which combined with the heat from the Earth, rearranges the carbon in organic molecules to form other compounds (animals tend to form crude oil, plants tend to form coal and natural gas)

5

Percentage of anthropogenic CO2 emissions caused by cement manufacture

Manufacturing

Contributes to roughly half of cement industry carbon emissions as calcium carbonate is heated to produce lime and CO2

Burning of fossil fuels

Contributes to roughly half of cement industry carbon emissions as heat is provided to carry out the process itself

900

Kg of CO2 emitted for every 1000kg of cement produced

Wildfires and volcanic eruptions

Main causes of any natural variation of the global carbon cycle

Anthropogenic variation of the global carbon cycle

Often caused by land use change, deforestation, farming practices, and hydrocarbon fuel extraction and burning (cement manufacture)

Ploughing

Farming technique that breaks down soil organic matter much more rapidly causing carbon to be lost from soil storage to the atmosphere - often complemented by emissions from farm tractors

25

Approximate percentage of human greenhouse gas emissions caused by agriculture and forestry

Enteric fermentation

The largest agricultural source of carbon emissions, when methane is released by livestock following digestion

30

Percentage of anthropogenic CO2 emissions said to be caused by land use change (mainly deforestation)

Main causes of deforestation

Need for extra agricultural land, logging, and urban sprawl

Slash and burn

Method of deforestation which is particularly harmful as it causes significant soil degradation on top of the carbon already being emitted by the loss of forest cover itself

Natural cause of deforestation

Wildfires and subsequent overgrazing of land not allowing regrowth of forest

Afforestation/reforestation

Counteraction against deforestation that is rapidly growing globally and offsetting large amounts of tropical deforestation through increased temperate forests

Side effect of deforestation

Causes accelerated decay of carbon stores such as litter due to increased sunlight radiation exposure for ground level

Urban growth

Factor increasing CO2 emissions through increased cement manufacture, transport, industry, and domestic energy use

Geologic carbon sequestration

CO2 is captured from its source e.g. power plants and then injected in liquid form typically in depleted oil/gas reserves or the deep ocean (despite risk of ocean acidification)

Terrestrial carbon sequestration

The use of plants to capture CO2 from the atmosphere and store it as carbon in their stems/roots as well as the soil

Impact of increasing atmospheric CO2 on land

Increased temperatures have warmed land surfaces causing increased melting of land ice and increased rate of decay of dead organic matter, both of which consequently release more greenhouse gases from their carbon stores creating a positive feedback loop

Impact of increased atmospheric CO2 on oceans

Ocean acidification, ocean warming, coral bleaching, melting sea ice

30

Percentage of CO2 released into the atmosphere that has dissolved into the oceans through direct chemical exchange to create carbonic acid (ocean acidification)

Ocean acidification

When carbonic acid formed by CO2 dissolving into oceans reacts with carbonate ions to form bicarbonate causing a lack of carbonate ions in oceanic ecosystems and make the slightly alkaline oceans more acidic

Implications of ocean acidification

Many marine species such as coral and plankton rely on carbonate to create calcium carbonate shells, with less carbonate available, their shells become thinner and more fragile, threatening marine biodiversity and disruption to food webs

500 million

Amount of people worldwide that coral reefs provide food and livelihood security for. Loss of carbonate ions and the consequent loss of marine biodiversity caused by ocean acidification will threaten these people with reduced food availability

Chalk and limestone

Calcium carbonate rocks that ocean acidification will better dissolve which will over time soak up even more CO2 from the atmosphere due to increased release of carbonate ions into the ocean increasing its carbon capacity (evaluation point of ocean acidification)

Phytoplankton

Species that grow better in cooler oceans and are fundamental to the oceans biological carbon pump, warmer oceans will decrease their populations and hence the effectiveness of the carbon pump, creating a potential positive feedback loop. However, increased oceanic CO2 could counteract this as they photosynthesise and hence grow by taking CO2 from the water

More heat absorbent water

What replaces sea ice when it is melted due to global warming causing more radiation to be absorbed by the planet and hence a positive feedback loop of further global warming

3.1mm

Rate at which global sea levels have been rising per year since the early 1990s due to both melting of ice and thermal expansion (water expanding as it heats up)

Geo-sequestration

Capturing greenhouse gas emissions from power stations and pumping them into underground reservoirs

Radiative forcing

The imbalance between incoming solar energy and outgoing infrared radiation in Earth’s atmosphere

1/5

The proportion of Earth’s carbon stored in biomass that is stored in the Amazon Rainforest

19,368km2

Yearly rate at which the Amazon Rainforest was deforested between 2000-2007

4th

Brazil’s global rank as a climate polluter (mainly due to Amazon Rainforest deforestation and land use change)

75

Percentage of Brazil’s greenhouse gas emissions caused by deforestation and land use change in the Amazon

Albedo

Measure of a surface’s reflectivity of solar radiation. Heavy slash and burn presence in the Amazon is causing this and surface run-off to increase in the Amazon causing drying of the area, harming ecosystems and drainage basins

Shallow cumulous clouds

Formed by moisture evaporated by deforested areas in the Amazon. Typically does not produce much rain

33-24

Difference in average temperature in degrees between rainforest land and deforested land in the Amazon

20

Percentage of the Amazon Rainforest that has already been deforested

Attempts to mitigate deforestation in the Amazon Rainforest

Creation of national parks and forest reserves, reforestation, agreements such as the Amazon Co-operation Treaty Organisation (ACTO) to promote harmonious development