The carbon cycle

Question 1

what are the key features of carbon?

Answer 1

-it is a solid, black element which bonds easily with other molecules and so is found in many forms
-the main compounds of carbon are carbon dioxide, methane, calcium carbonate, hydrocarbons ( fossil fuels ) and biomolecules ( organic molecules including carbohydrates, proteins, DNA etc. )
-it plays a major role in regulating global climate, particularly temperature and the acidity of rain, rivers and oceans

Question 2

how is carbon stored in the lithosphere?

Answer 2

-over 99.9% of the carbon on earth is stored in sedimentary rocks, such as limestone ( CaCO3 ), and marine sediments
-about 0.004% is stored in fossil fuels, such as coal and oil, in the lithosphere
-organic forms of carbon include litter, organic matter and humic substances found in soils

Question 3

how is carbon stored in the hydrosphere?

Answer 3

-CO2 is dissolved in rivers, lakes and oceans
-the oceans are the second largest carbon store on earth, containing approximately 0.04%, with the majority found in the deep layer of water in the form of dissolved inorganic carbon
-a small amount is found at the ocean surface where it is exchanged with the atmosphere

Question 4

how is carbon stored in the atmosphere?

Answer 4

-contains about 0.001% of the earth’s carbon, mainly as CO2 and CH4 ( greenhouse gases )
-human activity has caused CO2 levels in the atmosphere to increase by around 40% since the industrial revolution

Question 5

how is carbon stored in the biosphere?

Answer 5

-contains about 0.004% of the earth’s total carbon, 19% of which is stored in the tissues of plants which is transferred to the soil ( pedosphere ) when they die and decay
-others stores include plant litter, soil humus, peat and animals
-global stores are unevenly distributed, e.g. the oceans are larger in the southern hemisphere and storage in the biosphere mostly occurs on land, so terrestrial plant storage is focussed in the tropics and the northern hemisphere

Question 6

how is carbon stored in the cryosphere?

Answer 6

-contains less than 0.01% of the earth’s carbon, most of which is in the soil in areas of permafrost ( permanently frozen ground ) where decomposing plants and animals have frozen into the ground

Question 7

how much carbon is stored in each of the earth’s subsystems?

Answer 7

-lithosphere = 60-100 million Gt
-hydrosphere = 38,000 Gt
-atmosphere = 750 Gt
-biosphere = 3170 Gt
-pedosphere = 2300 Gt
-cryosphere = 1700 Gt

Question 8

how long is carbon stored in each of the earth’s subsystems?

Answer 8

-lithosphere = 240-300 million years
-hydrosphere = surface 25 years, deep 1250 years
-atmosphere = 6 years
-biosphere = 18 years
-pedosphere = days to 1000s of years
-cryosphere = 1000s of years

Question 9

what is the carbon cycle?

Answer 9

-the process by which carbon is stored and transferred
-it is a closed system as there are inputs and outputs of energy, but the amount of carbon in the system remains the same

Question 10

how does carbon flow between the major stores in the carbon cycle?

Answer 10

-long-term / slow carbon cycle = the movement of carbon between the atmospheric, oceanic and lithospheric stores, which takes between 100 and 200 million years
-short-term / fast carbon cycle = the movement of carbon from living things to the atmosphere and oceans, which moves up to 1000 times more carbon in a much shorter space of time

Question 11

what is the difference between a net carbon source and sink?

Answer 11

-net carbon source = releases more carbon into the atmosphere than it absorbs, e.g. the burning of fossil fuels or volcanic eruptions
-net carbon sink = absorbs more carbon from the atmosphere than it releases, e.g. plants, the ocean and soil

Question 12

what factors ( i.e. flows ) drive the change in magnitude of carbon stores?

Answer 12

-photosynthesis
-respiration
-decomposition
-combustion
-ocean uptake and loss / oceanic carbon pumps
-carbon sequestration
-weathering

Question 13

what is photosynthesis?

Answer 13

-the process by which plants and phytoplankton use energy from the sun to react CO2 and water to produce glucose and oxygen, enabling them to grow
-this transfers carbon stored in the atmosphere to biomass, which is passed through the food chain and released through respiration and decomposition, helping to maintain the balance between oxygen and CO2 in the atmosphere

Question 14

what is respiration?

Answer 14

-the process by which plants and animals break down glucose for energy, releasing CO2 and CH4
-this transfers carbon from living organisms in the biosphere to the atmosphere
-over geologic time, there has been more O2 put into the atmosphere and CO2 removed by photosynthesis than the reverse by respiration as not all organic matter is oxidised

Question 15

what is decomposition?

Answer 15

-the process by which decomposers ( e.g. bacteria and fungi ) break down the cells and tissues in dead organisms into smaller organic or inorganic matter, releasing CO2 and CH4
-this transfers carbon from dead biomass to the atmosphere and the soil in the form of humus

Question 16

why is decomposition important?

Answer 16

-it ensures that the important elements of life ( C, H, O, N, P, S, Mg ) can be continually recycled into the soil and made available for life
-e.g. plants need a supply of N, P and S atoms from the soil in addition to the C, H and O atoms from photosynthesis to make its DNA molecules
-therefore, plant growth is limited by the availability of mineral ions in the soil and the reactants in photosynthesis, which impacts the carbon cycle because decomposition enables plants to grow and store carbon in the biosphere before returning it back to the atmosphere by respiration and decomposition to be taken up again by photosynthesis

Question 17

what is combustion?

Answer 17

-the process of burning fossil fuels or organic matter in the presence of oxygen to release CO2, H2O and energy
-this transfers carbon stored in living, dead or decomposed biomass ( including peaty soils ) to the atmosphere

Question 18

what is ocean uptake and loss / oceanic carbon pumps?

Answer 18

-CO2 is directly dissolved from the atmosphere into the ocean, and transferred to the oceans when it is taken up by organisms that live in them ( e.g. plankton )
-carbon is also transferred from the ocean to the atmosphere when carbon-rich water from deep in the oceans rises to the surface and releases CO2

Question 19

what is the process of vertical deep mixing?

Answer 19

-CO2 is more soluble as the temperature of the water decreases, so more CO2 can dissolve into colder water, which occurs at the ocean surface due to the close proximity to the atmosphere
-warm water in oceanic surface currents is carried from the warm tropics to the cold polar regions where the water is cooled, making it dense enough to sink below the surface layer
-when cold water returns to the surface and warms up again, it loses CO2 to the atmosphere
-this ensures that CO2 is constantly being exchanged between the ocean and the atmosphere by acting as an enormous carbon pump

Question 20

what is meant by the biological pump?

Answer 20

-the process by which inorganic carbon ( CO2 ) is fixed into organic carbon by photosynthesis and then sequestered away from the atmosphere by transport into the deep ocean

Question 21

what is the process of the biological pump?

Answer 21

-marine organisms sequester carbon when they photosynthesise and so it gets incorporated into them as organic matter or structural CaCO3
-when organisms die, their dead cells, shells and other parts sink into deep water where they decay and decompose, releasing CO2
-some material sinks right to the bottom of the ocean where it forms layers of carbon-rich sediments, and burial by overlying layers can eventually turn these sediments into sedimentary limestone

Question 22

what is carbon sequestration?

Answer 22

-the capture of CO2 from the atmosphere, or anthropogenic ( human ) CO2 from large-scale stationary sources like power plants before it is released to the atmosphere, before it is put into long-term storage
-carbon from the atmosphere can be sequestered ( captured and held ) in sedimentary rocks or as fossil fuels ( until we burn them ) which form over millions of years when dead animal and plant material in the ocean falls to the floor and is compacted

Question 23

what is weathering?

Answer 23

-the breakdown of rocks in situ by a combination of weather, plants and animals, which transfers carbon from the atmosphere to the hydrosphere and biosphere

Question 24

what is the geological component of the carbon cycle?

Answer 24

-where the carbon cycle interacts with the rock cycle in the processes of weathering, burial, subduction and volcanic eruptions
-atmospheric carbon reacts with water vapour to form carbonic acid, which reaches the surface as rain and dissolves rocks through chemical weathering
-mineral ions are carried in surface waters like streams and rivers to the ocean where they settle out as minerals ( e.g. calcite ) and react with dissolved CO2 to form CaCO3, which is used by sea creatures ( e.g. to make shells )
-when marine organisms die, their skeletons sink to the bottom of the oceans where they collect as sediment, and burial by overlying layers can eventually turn these sediments into sedimentary limestone
-subduction causes the sea-floor deposits to heat up in the mantle, melt and then rise back up to the surface through volcanic eruptions, returning CO2 to the atmosphere

Question 25

how do carbon flows happen over different time and spatial scales?

Answer 25

-fast carbon flows ( e.g. photosynthesis, respiration, decomposition and combustion ) quickly transfer carbon between sources, which only takes a matter of minutes, hours or days -in contrast, sequestration is a slow carbon flow, which takes millions of years for carbon to be sequestered in sedimentary rocks -they also depend on spatial scale, e.g. at a plant scale, respiration and photosynthesis are the main flows, at an ecosystem scale, carbon flows such as decomposition and combustion also occur, whereas at a continental scale, all of the carbon flows including sequestration occur

Question 26

what are the natural drivers of combustion / change in the carbon cycle over time?

Answer 26

-wildfires -volcanic activity

Question 27

how do wildfires drive change in the carbon cycle over time?

Answer 27

-burning rapidly transfers large quantities of carbon from biomass or soil to the atmosphere as CO2, and loss of vegetation decreases photosynthesis so less carbon is removed from the atmosphere -in the longer term, fires can encourage the growth of new plants, which take in carbon from the atmosphere for photosynthesis, and some plants need wildfires to grow as it reduces competition for space -therefore, depending on the amount and type of regrowth, fires can have a neutral effect on the amount of atmospheric carbon -however, increasingly large and more frequent fires ( possibly made worse by warming temperatures and changing precipitation levels ) can change the carbon balance

Question 28

how does volcanic activity drive change in the carbon cycle over time?

Answer 28

-carbon ( stored in rocks within the earth for millions of years ) is released to the atmosphere, mainly as CO2, during volcanic eruptions -today, between 130 and 380 million tonnes of CO2 is released annually through volcanic eruptions, which is relatively low compared to millions of years ago and the 30 billion released by human activities, so they contribute a fairly low proportion of CO2 to the overall carbon cycle -however, there is the potential for a very large eruption to significantly disrupt the carbon cycle by reducing photosynthesis rates ( thus also affecting the water cycle ), e.g. the 1815 Mt Tambora eruption in Indonesia emitted SO2 which entered the atmosphere, reducing insolation and lowering global temperatures by 0.4-0.7°C in 1816

Question 29

what are the human / anthropogenic drivers of change in the carbon cycle over time?

Answer 29

-hydrocarbon ( fossil fuel ) extraction and burning -deforestation -farming practices -land use change

Question 30

how does hydrocarbon extraction and burning drive change in the carbon cycle over time?

Answer 30

-dead plants or animals that were unable to decompose millions of years ago ( due to the lack of oxygen ) turned into fossil fuels following burial due to the pressure from multiple layers of sediment -extracting and burning / combusting fossil fuels to produce energy releases CO2 into the atmosphere, but without human intervention, the carbon would remain sequestered in the lithosphere for thousands or millions of years to come -also, extraction processes destroy the environment and biodiversity is lost, which reduces the availability of vegetation to photosynthesise the CO2 from the atmosphere -since the industrial revolution, carbon flows from the lithosphere to the atmosphere much faster than it would do so naturally, e.g. global energy-related CO2 emissions rose to a historic high of 33.1 Gt in 2018, with electricity generation accounting for just over 60% of the 1.7% growth since 2017 ( mostly in China, India and the USA due to coal burning )

Question 31

how does deforestation drive change in the carbon cycle over time?

Answer 31

-forests may be cleared for agriculture, logging, or to make way for developments which reduces the size of the carbon store, and if this involves the burning of above-ground biomass, there is a rapid flow of carbon from the biosphere to the atmosphere -also, the removal of vegetation decreases photosynthesis and respiration, increasing the amount of atmospheric carbon

Question 32

how do farming practices drive change in the carbon cycle over time?

Answer 32

-when soil is ploughed, the layers invert, air mixes in, and soil microbial activity increases so organic matter is broken down much more rapidly, releasing carbon stored in the pedosphere into the atmosphere -livestock ( pastoral farming ) accounts for 14.5% of all anthropogenic carbon emissions as CH4 is released when they digest food ( enteric fermentation ) and CO2 is released when they respire -arable farming also increases the concentration of greenhouse gases in the atmosphere as growing rice in rice paddies releases a lot of methane ( making up 10% of total agricultural emissions ) -as the world's population has risen, so has food production and the use of agricultural machinery, meaning that carbon emissions from farming practices have increased

Question 33

how does land use change drive change in the carbon cycle over time?

Answer 33

-as well as deforestation, the change of land use from natural or agricultural to urban is a major source of carbon -this is because vegetation is removed to make way for buildings, reducing carbon storage in the biosphere, and the cement manufacture required for all the buildings and infrastructure releases lots of CO2

Question 34

what is meant by the carbon balance / budget?

Answer 34

-the difference between the inputs of carbon into a subsystem and outputs of carbon from it -the balance of the inputs and outputs of a subsystem determines whether it acts as a carbon source ( outputs outweigh inputs ) or a carbon sink ( inputs outweigh outputs )

Question 35

what is the impact of the carbon cycle on the land?

Answer 35

-it allows plants to grow as if there was no carbon in the atmosphere, plants couldn't photosynthesise, and if there was no decomposition, dead plants would remain where they fell and their nutrients would never be recycled -changes in the carbon cycle can reduce the amount of carbon stored in the land, e.g. warmer temperatures caused by global warming are causing permafrost to melt, releasing carbon previously stored in the ground into the atmosphere -an increase in global temperatures could also increase the frequency of wildfires

Question 36

what is the impact of the carbon cycle on the oceans?

Answer 36

-CO2 is dissolved directly into the oceans from the atmosphere where it is used by organisms such as phytoplankton and seaweed during photosynthesis and by other marine organisms to form calcium carbonate shells and skeletons -increased levels of CO2 in the atmosphere can increase the acidity of the oceans because the oceans initially absorb more CO2 ( leaving as much as 20% in the atmosphere ), e.g. since 1750, the pH of the ocean's surface has dropped by 0.1 / 30% -carbonic acid reacts with carbonate ions in the water to form bicarbonate, which means that there are less carbonate ions available for marine organisms like coral to build their shells, resulting in them being thinner and more fragile and a reduction in biodiversity -this threatens the survival of coastal communities through e.g. reduced food availability and increased storm surges -also, global warming can affect oceans, e.g. organisms that are sensitive to temperature ( such as phytoplankton ) may not be able to survive at higher temperatures so their numbers decrease, meaning that less CO2 is used by them for photosynthesis and removed from the atmosphere -warmer water is also less able to absorb CO2, so as temperatures rise the amount of CO2 that could potentially be dissolved in the sea decreases along with the effectiveness of the oceans as a carbon sink

Question 37

what is the impact of the carbon cycle on the atmosphere and climate?

Answer 37

-the carbon cycle affects the amount of gases containing carbon ( e.g. CO2 and CH4 ) in the atmosphere, which are greenhouse gases and so trap some of the sun's energy before re-emitting it in all directions, keeping the planet warm ( greenhouse effect ) -as the concentrations of GHGs in the atmosphere increase ( e.g. due to human activities ), temperatures are expected to rise ( i.e. global warming ) -changes in temperature across the globe will affect other aspects of climate, e.g. more intense storms are predicted

Question 38

what is an example of a positive and negative feedback loop in the carbon cycle?

Answer 38

-positive = greenhouse effect increases, so temperatures rise and thus the rate of respiration in plants increases, increasing the amount of CO2 ( a GHG ) in the atmosphere, which enhances the greenhouse effect -negative = atmospheric CO2 increases, which causes more plant growth and so plants remove and store more CO2 from the atmosphere, which in turn reduces atmospheric CO2

Question 39

what is the relationship between the water and carbon cycle in the atmosphere?

Answer 39

-carbon combines with water in the atmosphere to form carbonic acid, which allows chemical weathering and removes carbon from the atmosphere ( part of the slow carbon cycle ) -plants use water and CO2 during photosynthesis to produce oxygen and glucose, and during respiration, plants and animals release water and CO2 back into the atmosphere -the amount of CO2 in the atmosphere affects global temperatures, which affect the amount of evaporation that can take place and thus the amount of precipitation -CO2 causes about 20% of the earth's greenhouse effect, water vapour 50% and clouds 25% -when CO2 concentrations rise, air temperatures go up, so the oceans warm up and more water vapour evaporates into the atmosphere, which then amplifies greenhouse heating ( positive feedback loop )

Question 40

what are the relative impacts of the main GHGs?

Answer 40

-most abundant = CO2 ( 394ppm ) -strongest effect = halocarbons ( 1000x more warming than CO2 ) -longest atmospheric lifetime = halocarbons, nitrous oxide and CO2 ( around 100 years, compared to 12 years for CH4 )

Question 41

what is the greenhouse effect?

Answer 41

-insolation passes through the atmosphere and is either reflected back to space or absorbed by the earth's surface -the absorbed solar radiation is re-emitted as IR, and in the atmosphere, some IR is absorbed by GHGs and then re-emitted in all directions, warming the earth's surface

Question 42

what is meant by radiative forcing?

Answer 42

-the amount that the earth's energy budget is out of balance / the difference between the incoming solar energy absorbed by the earth and energy radiated back to space -radiative forcing has increased from negligible in 1750 to around 2.8 watts/m2 in 2023 due to increased GHG emissions and changing albedos as a result of land use changes ( enhanced greenhouse effect )

Question 43

how does climate change affect life on earth?

Answer 43

-the pattern of precipitation is expected to change, with wet areas getting wetter and dry areas getting drier, which could cause water shortages in some areas and potentially lead to conflicts in the future -agricultural productivity will decrease in some areas, which could lead to food shortages -extreme weather events ( e.g. storms, floods and droughts ) are predicted to get more frequent, which will affect less developed countries the worst as they are less able to deal with the impacts -further sea level rise will flood coastal and low-lying areas -the geographical range of some species will change as climate changes, so the arrival of new species in an area may damage the ecosystem and some species may become extinct -plankton numbers may decline if temperatures increase, which will have a knock-on effect on marine food chains

Question 44

what is the impact of the enhanced greenhouse effect on the ocean?

Answer 44

-ocean warming causes sea ice to melt, resulting in a positive feedback loop as the highly reflective ice is replaced by water ( lower albedo ) so the ocean is able to absorb more sunlight, which in turn amplifies the warming that caused it to melt in the first place -sea ice provides a habitat for algae and so the loss of it affects marine life all the way up the food chain ( e.g. from fish to polar bears ), leading to population declines due to the increased competition for resources -a decrease in salinity in the deep North Atlantic has been observed due to the melting of freshwater ice ( e.g. in Greenland ), which has been linked to a possible slowing down of the large-scale thermohaline oceanic circulation in the North-East Atlantic, raising concerns about a reduction in the amount of carbon that can be stored in the deep ocean

Question 45

by how much are sea levels rising and why?

Answer 45

-a rate of 3.1 mm/year since the early 1990s -due to the melting of terrestrial ice and thermal expansion as when water heats up, it expands

Question 46

how are humans trying to influence the carbon cycle and mitigate climate change?

Answer 46

-on an individual scale, people can choose to use their cars less and buy more fuel efficient cars, and make their homes more energy efficient, e.g. with double glazing, insulation and more efficient appliances -on a regional and national scale, governments can reduce reliance on fossil fuels for heating and powering homes by increasing the availability and affordability of renewable energy sources such as wind, tidal and solar, invest in afforestation and carbon capture and storage ( CCS ) and planners can increase the sustainability of developments by improving public transport ( to reduce car use ) and creating more green spaces -on a global scale, countries can work together to reduce emissions by means of IGOs, e.g. the Intergovernmental Panel on Climate Change ( IPCC ) was set up by the UN in 1992 to share knowledge about CC which has since provided the basis for the Kyoto Protocol ( 1997 ) and the Paris Agreement ( 2015 ), two international treaties to control the total amount of GHGs released by human activities in order to prevent large temperature rises -there are also international carbon trading schemes in which countries and businesses are given a limit on the emissions they can produce, so if they emit less they can sell the extra credits and if they produce more they need to buy more credits, discouraging unsustainable practices by creating economic consequences

Question 47

what are the two main types of carbon capture and sequestration ( CCS )?

Answer 47

-geologic ( geo-sequestration ) = CO2 is captured at its source ( e.g. power plants or industrial processes ) and then injected in liquid form into stores underground ( e.g. depleted oil and gas reserves or the deep ocean ) -terrestrial / biologic = plants capture CO2 from the atmosphere and store it as carbon in their stems and roots, as well as in the soil

Question 48

what is an example of geologic CCS?

Answer 48

-Boundary Dam, Canada is a coal-fired power station complex that has been retrofitted to capture 90% of its CO2 output ( 1 million tonnes per year ), which will be piped 66km to the Weyburn Oil Unit and injected 1,500m underground -it cost $800 million to build and consumes 21% of the coal plant's power output to scrub out the CO2 and compress it into a liquid for burial, but it is hoped that this cost will be offset by the extra oil recovered from the Weyburn oil field

Question 49

what are the advantages of geo-sequestration?

Answer 49

-it can capture up to 90% of CO2 emissions produced from the use of fossil fuels in electricity generation and industrial processes, preventing GHGs from entering the atmosphere -CCS systems can be integrated into existing power plants and could be used to forcibly extract a greater % of oil and gas out of existing reservoirs due to the pressure created by injecting the CO2 underground ( a process called enhanced oil recovery ), which would partly pay for the cost of the CCS technology -there are various methods of storage ( e.g. in sedimentary rocks or the ocean ), so it can be deployed in many different locations

Question 50

what are the disadvantages of geo-sequestration?

Answer 50

-high energy and financial costs for operation and maintenance -requires significant infrastructure and technological development -potential environmental impacts from transportation, storage and disposal of captured CO2 -EOR promotes the use of fossil fuels, releasing more GHGs which contribute to further climate change -underwater storage of captured CO2 can cause acidification of the oceans

Question 51

what are the advantages of terrestrial sequestration?

Answer 51

-it has the potential to increase the world's forest cover by 0.9 billion ha without affecting existing cities or agriculture -protection of existing forests will preserve current carbon sinks -afforestation and restoring degraded forests increases biomass density and thus carbon uptake by the biosphere -trees in croplands ( silviculture ) and orchards can store carbon both above and below ground and reduce CO2 emissions if they are grown as a renewable source of fuel

Question 52

what are the disadvantages of terrestrial sequestration?

Answer 52

-a forest might lose the captured carbon back to the air in a catastrophic forest fire or if it suffers disease / infestation -land-based sequestration plantations are slow growing and require active monitoring and management for many decades -carbon is never removed permanently from the atmospheric system as plants respire and return some to the atmosphere -trees lower the albedo in deserts ( e.g. Israel ) which causes warming -planting monocultures decreases biodiversity and facilitates the spread of disease

Question 53

how could improved aviation practices help to mitigate climate change?

Answer 53

-in 2019, the global aviation industry carried 4.5 billion passengers, producing 915 million tonnes of CO2 -design and technology = increased energy efficiency ( e.g. the Airbus A380 and Boeing 787 both use less than 3 litres of fuel per 100 passenger km ), increased use of biofuels ( renewable energy ), carbon capture within the engines, maximising the number of seats per aircraft -movement management = towing aircraft while on the ground, avoiding circling and queuing, adopting fuel efficient routes -flight management = 100% occupancy of seats, cruising at lower speeds, matching an aircraft to the route -however, aviation only accounted for 2.5/20% of global CO2 emissions from transport in 2023

Question 54

what is an example of a tropical rainforest and why is it important?

Answer 54

-the Amazon Basin is the world's largest rainforest and one of the most biodiverse, with 300 billion trees and 15,000 species which store 1/5 of all the carbon in the planet's biomass and release vast amounts of water vapour into the atmosphere through EVT, contributing to cloud formation and precipitation -it receives over 2,000mm of rainfall annually -it is home to over 500 species of mammals and 2000 species of fish, many of which are endangered ( such as the Amazonian manatee, black caiman and pirarucu ) -it covers 40% of the South American landmass ( i.e. 9 countries ) and is home to 34 million people who depend on the resources it provides

Question 55

how has the amount of carbon absorbed by and stored in the Amazon changed over time and what is the impact of this?

Answer 55

-decreased from 2 billion tonnes per year in the 1990s to 600 million tonnes in 2019, storing a total of 76 billion tonnes and forming a carbon sink of 1-3 GtC/year -the increasing concentration of CO2 in the atmosphere has led to increased productivity in the Amazon rainforest because the vegetation is able to access more CO2 for photosynthesis, so the amount of biomass has been increasing -however, although trees are growing more quickly, they are also dying younger, so we may not be able to rely on the Amazon rainforest to continue to be such an effective carbon sink in the future, e.g. the south-eastern part of the forest ( about 20% of the total area ) has become a carbon source and lost its ability to absorb large quantities of CO2

Question 56

what are the human drivers of change in the Amazon?

Answer 56

-deforestation -climate change

Question 57

how does deforestation drive change in the Amazon?

Answer 57

-agriculture = soybean production leads to extensive clearing, and in Brazil, cattle ranching accounts for approximately 80% of deforested land in the Amazon as vast amounts of forest are cleared to create space to graze cattle -commercial and illegal logging = trees are cut down for timber which is sold for e.g. construction and furniture, so selective logging targets high-value trees like mahogany and teak but often leads to further forest degradation -mineral extraction ( e.g. gold, iron ore and bauxite ) = Carajás Mine, the world's largest iron ore mine, has led to extensive deforestation as mining operations often require the construction of roads, staff housing and other infrastructure -infrastructure development = building roads ( e.g. the Trans-Amazonian Highway ) opens up remote areas of forest for agriculture, logging and mining, and building dams and reservoirs ( e.g. the Belo Monte Dam ) floods vast areas of forest, leading to habitat loss and ecosystem disruption

Question 58

how does deforestation impact river water quality?

Answer 58

-the soils are exposed to the heavy tropical rainfall due to the increase in surface runoff, which rapidly washes away the topsoil and erodes the deep weathered layer below -most of the soil is washed into rivers before the forest clearance has caused a reduction in the rainfall, so the amount of silt in the river increases and water quality decreases

Question 59

what is the impact of deforestation on the water cycle?

Answer 59

-there is no tree canopy to intercept rainfall, so more water reaches the ground surface but there is too much to infiltrate into the soil, so instead the water moves to rivers as surface runoff, which increases the risk of flooding -the rate of EVT is reduced, meaning that less water vapour reaches the atmosphere, fewer clouds form and rainfall is reduced, which increases the risk of drought

Question 60

what is the impact of deforestation on the carbon cycle?

Answer 60

-without roots to hold the soil together, heavy rain washes away the nutrient-rich top layer of soil, transferring carbon stored in the soil to the hydrosphere -there is less leaf litter, so humus isn't formed and the soil cannot support much new growth, which limits the amount of carbon that is absorbed -trees remove CO2 from the atmosphere and store it, so fewer trees means more atmospheric CO2, which enhances the greenhouse effect and global warming

Question 61

how does climate change drive change in the Amazon?

Answer 61

-in some areas, temperature is increasing and rainfall is decreasing, which leads to drought, e.g. the Amazon had severe droughts in 2005 and 2010 which resulted in widespread forest fires and significant deforestation -plants and animals living in tropical rainforests are adapted to moist conditions, so many species die in dry weather, and frequent or long periods of drought could lead to extinction of some species, in addition to forest fires, which can destroy large areas of forest, releasing lots of CO2 into the atmosphere -scientists predict that a 4°C temperature rise could kill 85% of the Amazon rainforest, which would result in lots of carbon being released into the atmosphere as the dead material decomposed, and less CO2 being taken in from the air by trees for photosynthesis

Question 62

what attempts are there to limit human impacts on the Amazon?

Answer 62

-selective ( sustainable ) logging -reforestation -environmental laws -protection and conservation programs -ecotourism

Question 63

how does selective logging mitigate climate change in the Amazon?

Answer 63

-only some trees ( e.g. just the oldest ones ) are felled, so most are left standing -this is less damaging to the forest because if only a few trees are taken from each area, the forest structure is kept ( i.e. the canopy is still there and the soil isn't exposed ), allowing the forest to regenerate naturally so the impact on the water and carbon cycle is small and timber resources remain available for future generations -this provides economic opportunities and supports local economies through job creation, maintains forest health and encourages the use of sustainable practices, reducing illegal logging activities, but monitoring and enforcement of sustaible practices can be challenging

Question 64

how does reforestation mitigate climate change in the Amazon?

Answer 64

-new trees are planted to replace the ones that are cut down, e.g. a project in Peru replanted over 115 acres of forest between 2016 and 2019 -it's important that the same types of tree are planted so that the variety of trees is kept for the future and the local carbon and water cycles return to their initial state

Question 65

how do environmental laws mitigate climate change in the Amazon?

Answer 65

-laws that ban the use of wood from forests that aren't manage sustainably, ban excessive logging and control land use ( e.g. the Brazilian Forest Code says that landowners have to keep 50-80% of their land as forest ) can help protect rainforests -the Amazon Cooperation Treaty Organisation ( ACTO ) was formed when all 8 Amazonian countries signed the ACT on 3 July, 1978 to promote harmonious development and resource management by creating programs and establishing agreements, e.g. the Manaus Declaration in 2004 coordinated the sustainable development of 2.9 million square miles of rainforest

Question 66

how do protection and conservation programs mitigate climate change in the Amazon?

Answer 66

-many countries have set up national parks and nature reserves to protect rainforests, e.g. the Central Amazon Conservation Complex ( CACC ) in Brazil was set up in 2003 and protects biodiversity in an area of 49,000 km2 while allowing local people to use the forest in a sustainable way -within these protected areas, damaging activities such as hunting and logging can be monitored and prevented, preserving large tracts of rainforest from deforestation and degradation -however, this can limit access to natural resources for local communities, potentially affecting their livelihoods

Question 67

how does ecotourism mitigate climate change in the Amazon?

Answer 67

-this promotes conservation by providing economic incentives to protect natural areas, e.g. the Yachana Lodge in Ecuador ( a remote area of the Amazon ) employs local people and supports community development while minimising environmental impacts -visitors learn about the rainforest and its conservation, fostering a deeper appreciation and commitment to its protection, which provides funding for conservation projects and wildlife protection, but environmental degradation can result if it's not managed properly ( e.g. over-visitation and habitat disturbance )