THE CARBON CYCLE

What are carbon stores, fluxes (transfers) and processes and give examples

• Stores = where carbon is held e.g sedimentary rocks, phytoplankton, coal, oil and gas

• Fluxes (transfers) = the flows which move carbon between stores e.g burning fossil fuels

• Processes = the physical mechanisms which drive the fluxes between stores e.g photosynthesis, diffusion

What do carbon stores operate as?

• Sources = adding carbon to the atmosphere

• Sinks = removing carbon from the atmosphere

The carbon cycle is balanced (or in equilibrium) when the sources equal the sinks

What is the geological carbon cycle?

• A long term process that moves carbon between the earths rocks, oceans and atmosphere over millions of years, with reservoir turnover rates of at least 100,000 years (the rate at which carbon enters and leaves a store)

• Organic matter buried deep in sediments are protected from decay which means it takes millions of years to turn into fossil fuels

• Carbon flows through volcanic eruptions, chemical weathering, erosion and sediment formation on the ocean floor

What is the bio-geochemical carbon cycle?

• The fast part of the carbon cycle which has large fluxes and rapid reservoir turnovers of a few years up to 1000 years

• Carbon is sequestered (captured) in and flows between the atmosphere, oceans, ocean sediments, vegetation, soils and freshwater

What are the geological processes in the carbon cycle?

• Weathering of rocks - Mechanical (breaking up of rocks through frost), chemical (breakdown of rocks by the carbonic acid in rain) and biological (breakdown of rocks via the roots of plants) weathering results in the breakdown of rocks

• Decomposition - Plant and animal particles from decomposition after death store carbon

• Transportation - Rivers can carry particles to the ocean, where they will be deposited

• Sedimentation - Over time, sediments build up, burying older sediments below e.g shale and limestone

• Metamorphosis - Pressure builds overtime in the layers of sediment - eventually leads to the sediment changing into rock e.g limestone becomes marble, shale becomes slate

• CARBON CAN TAKE BETWEEN 100 AND 200 MILLION YEARS TO MOVE BETWEEN ROCKS, THE SOIL, THE OCEAN AND THE ATMOSPHERE

Carbon in limestone and shale

• 80% of carbon containing rocks in the ocean is from shell-building organisms (corals) and plankton

• When coral and plankton fall to the ocean floor, they form layers and cement together eventually turning into limestone (lithification - loose sediments turning into rock)

• The remaining 20% of rocks contain organic carbon originating from organisms that have been embedded in layers of mud

• Heat and pressure compress the mud and carbon over millions of years to form sedimentary rock e.g shale

Carbon in fossil fuels

• Coal, oil and natural gas are known as fossil fuels because they have been formed from the remains of organic material over 300 million years ago

• When organic matter builds up faster than it can decay, the layers of organic carbon develop into coal, oil or natural gas instead of shale

What is volcanic outgassing, where does it happen at and how does it compare to human activity?

VOLCANIC OUTGASSING

• The earths crust contains pockets of carbon dioxide which can be easily disturbed by volcanic eruptions or seismic activity

• This release of gas that has been dissolved, trapped, frozen or absorbed in rock is called outgassing

WHERE DOES IT HAPPEN

• At plate boundaries, subduction zones and spreading ridges

• Areas with no current volcanic activity e.g the geysers in Yellowstone national park, USA

• Direct emissions from fractures in the earths crust

COMPARISON TO HUMAN ACTIVITY

• The gas released from volcanic eruptions is relatively insignificant in comparison to human activity:

  • Volcanoes currently emit about 0.3 to 0.4 gigatonnes of CO2 per year globally

  • Fossil fuel use emits about 35 gigatonnes

What is sequestering and photosynthesis?

• Sequestering = the movement of carbon into carbon stores which can therefore lower the amount of carbon in the atmosphere

• Photosynthesis (by land based plants and phytoplankton) = the main process responsible for sequestering carbon from the atmosphere

What is ocean sequestration?

• THE PROCESS BY WHICH THE OCEANS ABSORB AND STORE CARBON DIOXIDE FROM THE ATMOSPHERE (oceans are the largest carbon store on earth)

• The movement of carbon within oceans is controlled:

  • Vertically by carbon cycle pumps

  • Horizontally by thermohaline circulation

What are the carbon cycle pumps and what do they do?

• The carbon cycle pumps move carbon dioxide to the sea floor and to the ocean surface to be released into the atmosphere

• The pumps - Biological pump, Carbonate pump, Physical pump

What is the process of the biological pump?

1) Phytoplankton absorb CO2 from the atmosphere via photosynthesis (in the euphotic zone of the ocean)

2) The carbon is then transferred through the food chain via zooplankton and other organisms that eat phytoplankton

3) Respiration - Some carbon is released back into the water as CO2 through respiration

4) Decomposition - The organisms, shells and waste die and sink to the deep ocean as marine snow, and then accumulate as calcareous ooze

5) Long term storage - The calcareous ooze then becomes heated and compressed, over time forming limestone sediments / sedimentary rock (diagenesis - sediments turning into sedimentary rock)

What is the process of the carbonate pump?

1) Carbon dioxide from the atmosphere dissolves in the ocean forming carbonate ions in the water

2) Shell formation (calcification) - Marine organisms then take in these ions and combine them with calcium to form calcium carbonate shells

3) When these organisms die, their shells sink to the ocean floor, contributing to calcareous ooze

4) Over time, these sediments are buried through diagenesis and lithification forming rocks such as limestone

5) Long term storage - This process locks up carbon in the long-term carbon cycle and does not allow an easy return to the ocean surface

What is the physical pump (considered the most important transfer)?

1) CO2 from the atmosphere dissolves into the ocean surface and is then taken to the deep ocean stores through downwelling currents (cold water takes in moreCO2)

2) The Thermohaline circulation then distributes the carbon around the planet

3) Cold water absorbs more CO2, therefore as the equatorial water move towards the poles, more CO2 is absorbed

4) Salinity increases at the same time, making the water denser, therefore the water sinks (downwelling) taking CO2 from the oceans surface to the deep ocean stores

What is the Thermohaline Circulation?

• A global system of deep ocean currents driven by differences in temperature and salinity (salt content)

• These ocean currents are responsible for circulating carbon

• Warm surface waters lack nutrients and CO2 due to evaporation but they become enriched again through the circulation of currents

What is terrestrial sequestration?

• The process by which carbon dioxide is absorbed from the atmosphere and stored on land, mainly in vegetation and soils

• Has the shortest time scale of seconds, minutes or years

What is the process of terrestrial sequestration?

1) Plants take in CO2 from the atmosphere via photosynthesis and convert it into biomass (leaves, trunks, roots)

2) Dead plant material falls to the ground, decomposes and becomes soil organic carbon

3) Some carbon can remain locked in soils or peat for very long periods - a key carbon sink in the carbon cycle

What are the factors affecting soil capacity to store organic carbon?

CLIMATE:

• TEMPERATURE: cold conditions slow decomposition —> more carbon stored, warm conditions increase decomposition —> less carbon stored

• PRECIPITATION: Moderate rainfall supports plant growth (more carbon input), too much water can create waterlogged soils (can increase storage, e.g peat)

SOIL TYPE:

• CLAY: rich soils have a higher carbon content than sandy soil as clay protects carbon from decomposition

HUMAN ACTIVITY:

• Deforestation / farming —> reduce carbon storage

• Afforestation / conservation —> increase storage

• Globally, soils have lost 40 - 90 billion gigatonnes of carbon since 1850 through cultivation and disturbance

What is the greenhouse effect?

• The process by which certain gases in the atmosphere trap heat, keeping the earth warm enough to support life

• The natural greenhouse effect is influenced by the concentration of atmospheric carbon (carbon dioxide and methane)

What is the step by step process of the greenhouse effect?

1) Energy from the sun reaches the earths surface

2) The surface absorbs energy and re-emits it as long wave (infrared) radiation

3) Greenhouse gases (CO2, methane and water vapour) absorb this outgoing heat

4) Some heat is sent back towards the earth, warming the planet

NATURAL GREENHOUSE EFFECT KEEPS EARTH AT ABOUT +15°C instead of -18°C

What is the enhanced greenhouse effect?

• Human activities (burning fossil fuels, deforestation) increase greenhouse gases

• This strengthens the greenhouse effect, leading to global warming

What is the importance of soil?

• Stores 20-30% of global carbon mainly as soil or organic matter (humus)

• In semi arid and arid regions, soil is the main carbon store due to sparse vegetation

• They directly influence climate regulation as they are able to switch between sink and source (proportion of plant inputs to decomposition)

• Soil erosion is a major threat to carbon storage and soil health —> this is because organic carbon is mainly found in the surface soil layer

What is the relevance of fossil fuel combustion in the carbon cycle?

• Fossil fuels have been burnt at an increasing rate since the Industrial Revolution and remain the main energy source

• Without human activity, the carbon in fossil fuels would flow into the atmosphere very slowly through volcanic activity

• However, the burning of fossil fuels has increased this flow from slow to fast carbon cycling

• The balance of the carbon cycle has been altered by the burning of fossil fuels which has various impacts on:

  • Global climate

  • Ecosystems

  • The hydrological cycle

Implications of fossil fuel combustion for the climate?

• As a result of global warming, changing temperatures and salinity levels of the oceans could effect the Thermohaline current:

  • The North Atlantic Drift (NAD) also known as the Gulf Stream could slow or reverse

  • The NAD keeps the UK temperatures 5°C higher than they would be otherwise during the winter

What are the implications of fossil fuel combustion for ecosystems?

• Ecosystems help regulate carbon and hydrological cycles as well as providing goods and services for humans and the planet

• Already, species with low populations numbers, limited climatic ranges or restricted habitats are at risk

• Marine ecosystems are threatened by lower oxygen levels, higher rates of ocean acidification and food chain changes (resulting from rising temperatures)

• Coastal ecosystems are at risk from sea level rise

• Although most species will be impacted negatively, there are some that may benefit:

  • Cool, moist regions (e.g UK) could provide habitats for more species

What are the implications of fossil fuel combustion on the hydrological cycle?

• Increased evaporation rates leading to more moisture circulating the cycle

• Increase surface permafrost temperatures

• Reduction in ice caps, sea ice and glacier storage

• Changes in the capacity of terrestrial ecosystems to sequester carbon and store water

• Sequestration = to capture and store something so that it is kept out of circulation

What is energy security?

• Energy security is the uninterrupted, reliable access to affordable, sufficient, and sustainable energy supplies to meet a country’s or regions needs

What should energy supply be?

• Reliable and uninterrupted

• Affordable and competitively priced

• Accessible and available

• Dependent on domestic rather than imported sources

What are energy secure countries?

• Countries that will be able to meet all or most of their energy demands from within their country

What are uses of energy?

• Provides light

• Powers most forms of transport

• Warms and cools our home

• Vital to modern communication

• Drives most forms of manufacturing

Why is the consumption of energy demand increasing?

• Global population growth

• Development and rising of standard living

• The essential nature of energy to our everyday life

What is energy consumption measured in?

• Kilograms of oil equivalent per year (kgoe/yr)

• Gigajoules per year (GJ/yr) or Exajoules per year (EJ/yr)

• Megawatt hours per year (MWh/yr)

What is energy intensity?

• A measure of how efficiently a country is using its energy

What is energy mix? - give examples

• The combination of different energy sources that are used to meet a country’s total energy demand

• Countries have their own individual energy mix:

  • Developing countries usually use natural resources such as firewood for cooking

  • Emerging countries will see a rise of oil use as transport and car ownership increases

  • As countries develop they tend to start using more gas and nuclear power as technology advances

UK:

• 39.7% oil

• 36.2% gas

• 14.4% renewables

• 6.4% nuclear

• 3.3% coal

ICELAND

• 66.6% gas

• 19.2% hydro

• 12.5% oil

• 1.7% coal

What are primary energy sources and how are they used to generate electricity?

• Primary energy = The forms of energy found in nature that have not yet been converted into a secondary energy e.g electricity

• Primary energy sources are used to generate electricity which include:

  • Non-renewable fossil fuels such as coal, oil and natural gas

  • Renewable energy such as wind, geothermal, hydroelectricity and solar

  • Recyclable fuels such as nuclear energy, biomass and general waste

Why is it important that countries have a good balance between domestic energy sources and imported energy sources?

• Energy security increases as dependence on imported energy sources decreases

• A country that depends massively on imported energy is at risk from sudden threats such as:

  • Artificial and abrupt changes in energy prices

  • Energy supplies being cut off by civil unrest or military campaigns

What are the factors affecting the access to / the consumption of energy?

PHYSICAL AVAILABILITY:

• Domestic energy sources may be available, but they may not be easily accessible

• If energy sources are not available within the country, the energy will have to be imported (adding to the overall cost of energy to the consumer)

COST:

• There are a range of costs involved in the access and consumption of energy

  • The cost of the physical exploitation

  • The cost of processing (converting primary energy into secondary energy)

  • The cost of delivery to the consumer

TECHNOLOGY:

• Modern technology is very useful in the exploitation of energy e.g oil that requires deep drilling into the earth

• As a result of modern technology making energy sources more accessible, increasing energy consumption usually follows

CLIMATE:

• Regions such as North America, the Middle East and Australia have high levels of consumption as a result of the extra energy required to make the extremes of heat and cold more comfortable

What is the role of major players in the world of energy?

TNCs:

• Majority of these companies are involved in a variety of operations including exploring, extracting, transporting, producing and refining petrochemicals (chemical products made from crude oil e.g plastics)

Organisation of the Petroleum Exporting Countries (OPEC):

• OPEC currently has 13 member countries owning around two thirds of the oil reserves between them

• As a result, OPEC is able to control the amount of gas and oil in the global market along with their prices

• OPEC have been accused of forcing up the price of oil and gas by slowing the production / withholding

GOVERNMENTS:

• Can have an impact on how energy is sourced

• They look after energy security

CONSUMERS:

• Consumers tend to have little impact on energy prices

In the 20th century, what was the most used fossil fuel?

• In the 20th century, oil took over from coal as the most used fossil fuel

• However, today oil is now being challenged by gas as the number one fossil fuel

What is the mismatch between the supply and demand of coal, oil and gas?

COAL

• The consumption of coal is decreasing in comparison to oil and gas, however the production of it is increasing

  • China and the USA remain the two largest consumers of coal and are also the largest producers of coal

  • There is a small mismatch as the main producers of coal are usually the main consumers e.g China & USA

OIL

• Significant mismatch as the main suppliers of oil are members of OPEC and consumers are in Europe

GAS

• Gas supply is dominated by the USA and Russia and the major importers are Western European countries and Japan

Energy pathways - oil

• The Middle East is the number one producer of oil in the world

• Even though the USA produces oil, it imports oil from South America, West Africa and Europe to help meet the high demands

  • The USA is the largest oil consumer —> using more than 19 million barrels of oil per day

  • There is only one pathway from Russia which is to Europe

Energy pathways - coal

• There is still a significant global trade of coal

  • Three of the largest producers of coal (USA, China, India) also import coal e.g some burning plants in the USA still import coal from abroad as it is cheaper than buying USA produced coal

  • Australia and Indonesia export large amounts of coal to Japan, South Korea and Taiwan as well as China and India

Energy pathways - gas

• Energy pathways of gas a very similar to oil

  • Gas flows either directly through pipelines or in liquid form by tanker ships

  • There is a major pathway from Russia to Europe which is experiencing disruption

    • In 2021, around 50% of Russias crude oil was exported to European countries

    • Following Russias invasion of Ukraine in February 2022, many countries have pledged to stop or restrict oil or gas imports from Russia to hinder its war effort

What are the four main types unconventional fossil fuel sources?

TAR SANDS:

Nature - mixture of clay, sand, water and bitumen (a heavy, viscous oil)

Extraction - mined, then injected with steam to reduce the viscosity of the tar so it can be pumped out

Example - Biggest deposits are in Canada and Venezuela, tar sands produce about 40% of Canadas oil output

OIL SHALE:

Nature - Oil bearing rocks that are permeable enough to allow oil to be pumped out

Extraction - Mined or Shale is ignited so that the light oil fractions can be pumped out

Example - Little exploration has taken place

SHALE GAS:

Nature - a natural gas that is trapped in fine, grained sedimentary rock

Extraction - Fracking - pumping in water and chemicals forces out the gas

Example - the USA is the leading producer and exporter

DEEPWATER OIL:

Nature - Oil and Gas found offshore and at considerable oceanic depths

Extraction - Drilling takes place from ocean rigs

Example - Huge oil deposits were discovered off the coast of Brazil in 2006 and Brazil are leading the way in this

What are the alternative sources of clean energy?

• Renewable sources - Hydro, wind, solar, geothermal and tidal energy

• Recyclable sources - Nuclear power and biofuels

What will the physical geography of a country determine?

• The physical geography of a country will determine whether they have renewable energies to exploit

  • Not all countries will have coasts or “hot rocks” heated by magma for use in geothermal energy

  • Not all countries have warm climate with long sunshine hours

  • Not all countries have permanently flowing rivers or strong winds

What are the benefits and challenges of renewable energy?

BENEFITS:

• Will not run out

• Provides environmental benefits e.g reduction in greenhouse gases

• Will save money in the long term as operation and maintenance costs are lower

• Reduces a countries reliance on importing energy sources from abroad

• Creates employment e.g in the USA, the renewable energy sector employs three times the amount of people than the fossil fuel sector

CHALLENGES

• There are only a few countries where renewables will be able to replace fossil fuels completely - this is due to the intermittency of renewable energy and limitations associated with the physical geography of the country

• As a result of oil prices falling during 2015, renewable energy became less attractive due to its higher costs

• Can have negative impacts on the environment e.g flooding more valleys for HEP dams

• Many people will protest when there is a proposal made for a wind or solar farm close to their home

What are the issues associated with nuclear energy?

• SAFETY: Nuclear incidents such as Chernobyl (Ukraine) and Fukushima (Japan)

• DISPOSAL: Disposal of highly toxic radioactive waste (which has a long decay life)

• TECHNOLOGY: Technology used means that nuclear energy is only really open to the most developed countries

• COSTS: Despite operational costs being relatively low, the cost of building and decommissioning are high

• SECURITY: Security of nuclear powered stations at a time when international terrorism is a concern

What are Biofuels?

• A type of renewable energy made from biomass (organic materials) such as plants or animal waste

What are the two types of biofuels and the disadvantages?

• PRIMARY BIOFUELS: Include fuel wood, wood chips and pellets (small, compressed pieces of organic material) that are used unprocessed for heating, cooking or electricity

• SECONDARY BIOFUELS: Obtained from the processing of crops (e.g sugarcane, soybeans and maize/corn) where two types of fuel are extracted (bio-alcohol and biodiesel) which are used to fuel vehicles and generate electricity

Whilst biofuels can be considered a “green” source of energy, there are disadvantages, for example the impacts this can have on food supply

• For example, a hectare of space used to grow energy crops is a hectare less for growing much needed food

Radical technologies - What is carbon capture and storage (CCS)?

• The process of capturing the carbon dioxide released from power stations or industry and burying it deep underground

What are the challenges of carbon capture and storage?

• PRICE: It is expensive because of the advanced technology required

• UNCERTAINTIES: No one can be sure that the carbon dioxide will stay underground and that it will not leak to the surface and enter the atmosphere

Radical technologies - What are hydrogen fuel cells?

• Hydrogen fuel cells produce electricity by combining hydrogen and oxygen, with water as the only waste product

• They are considered to be one of the best strategies for reducing carbon emissions

How do hydrogen fuel cells work and what are they useful for?

• A fuel cell combines hydrogen and oxygen to produce electricity, heat and water

• A fuel cell will provide electricity as long as hydrogen is supplied and it will never lose its charge

USEFUL FOR…

• A source of heat and electricity for buildings

• A power source for electric vehicles

What are the causes of deforestation?

• Agriculture (biggest cause) - Forests cleared for farming crops e.g soy

• Resource extraction - Oil and gas

• Infrastructure - Building roads, damns and settlements

• Energy production - Land cleared for biofuels

DIRECT CAUSES: Agriculture, logging

INDIRECT CAUSES: Population growth, economic pressures

How does deforestation impact the water cycle?

• Reduced interception by vegetation so infiltration to soil and groundwater changes

• Increased erosion and surface runoff —> this therefore increases the sediment eroded and transported into rivers

How does deforestation impact the carbon cycle?

• Reduced carbon dioxide intake during photosynthesis

• Reduced storage in soil and biomass (organic material)

What is the difference between afforestation and reforestation and why can they be considered controversial?

• AFFORESTATION - Planting trees on land that never had forest or has been without forest for a long time

• REFORESTATION - Planting trees in places with recent tree cover, replacing lost primary forest

CONTROVERSY = Commercial trees such as palm oil often store less carbon, use more water and are prone to disease

What are the two main types of grassland?

• TEMPERATE GRASSLAND = A biome characterised by grasses, seasonal rainfall and a few trees e.g North America

• TROPICAL GRASSLAND or SAVANNAH = Scattered trees with a wet and dry season e.g Africas Serengeti

What is ocean acidification?

• OCEAN ACIDIFICATION = The process where the oceans pH is decreasing and they are becoming more acidic because they absorb more carbon dioxide from the atmosphere

Why is ecosystem resilience important in ocean acidification?

• If the rate of acidification is slow enough, the organisms may be able to adapt to the changes and be more resilient

What is coral bleaching?

• Occurs when coral loses its colour and turns white due to stress, usually from rising sea temperatures

What is the process of ocean acidification and why is it negative?

1) Carbon dioxide is released into the atmosphere from burning fossil fuels, deforestation etc…

2) Oceans absorb the carbon dioxide - they act as a carbon sink

3) The carbon dioxide then reacts with the sea water to form carbonic acid

4) The carbonic acid then releases hydrogen ions, lowering the pH

5) The carbonate ions and the hydrogen ions then react, causing a decrease in carbonate ions

WHY THIS MATTERS

• Organisms like coral and shellfish need carbonate ions to build shells - e.g coral bleaching in the Great Barrier Reef

• Less carbonate —> weaker shells and coral structures