Earth's Life Support Systems

Earth Basics

Earth's Atmosphere:

  • Earth has a breathable atmosphere.
  • 21% Oxygen, 0.04% Carbon Dioxide which is a poisonous gas but helps to keep the Earth warm.
  • Earth's atmosphere is kept on the planet by its pull of gravity.

Earth's Climate:

  • The temperature on Earth does not go from one extreme to the other (Mercury= -200 to 375 degrees celsius)

Earth's Light:

  • Earth takes 24 hours to spin on its axis so each side of the planet recieves light regularly (Venus= 243 days)
  • The Sun's gravity keeps the Earth in its orbit.
  • Earth's distance from the Sun means it recieves the perfect amount of heat and light to support life. (GOLDILOCKS ZONE- distance from sun allows the presence of H2O)
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Uses of water for flora, fauna and people

FLORA-

  • Need water for photosynthesis1, respiration2 and transpiration (Carbon Dioxide+Water = Oxygen and Glucose)1 (Oxygen+Glucose= Carbon Dioxide+ Water)2
  • Need water to maintain their rigidity and to transport mineral nutrients from the soil.

FAUNA AND PEOPLE-

  • Water is the medium used for all chemical reactions in the body including circulation of oxygen and nutrients. Water is a byproduct for when you sweat.
  • Essential resource for economic activity- generate electricity, irrigate crops, provide recreational facilities, satisfy public demand for drinking water and sewage disposal and for industries such as food manufacturing.
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Stores in the global water cycle

1. Lithosphere (1.7%) - the rigid outer part of the earth, consisting of the crust and upper mantle. It's divided into tectonic plates.

2. Biosphere (0.00004%)  - the space at the Earth's surface and within the atmosphere occupied by living organisms.

3. Hydrosphere (96.5%) - all the waters on the earth's surface, such as lakes and seas.

4. Cryosphere (1.7%) - the frozen part of the Earth's surface, including the polar ice caps, continental ice sheets, glaciers, sea ice and permafrost.

5. Atmosphere (0.001%) - the envelope of gases surrounding the planet.

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Water Stores 2

Oceans contain 97% of all water on the planet leaving only 3% as fresh water. Of this fresh water, 75% is frozen in the ice caps of Antarctica and Greenland. Water stored below ground in permeable rock amounts to just 20% of all fresh water. Given its pivotal role it is perhaps surprising that only a minute fraction of the Earth's water is found in the atmosphere. This is explained by the rapid flux of water in and out of the atmosphere: the average residence time of a water molecule is just 9 days.

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Global Hydrological Cycle

  • The total amount of water in the cycle is always the same: no water enters or exits.
  • Energy from the  sun enters and leaves the system and is required to 'drive' the system.
  • It is a closed system.
  • Stores are said to 'flux'- amount of water changes constantly.
  • Processes/ flows are physical mechanisms which drive the flux of material between stores.
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Drainage Basin System

  • Energy comes into and leaves the drainage basin system. 
  • Mass can also enter and leave.
  • Therefore it is an open system.
  • A drainage basin is an area of land drained by a river and its tributaries (river system). It includes water found in the water table and surface run-off. 
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Processes in Hydrological System 1

Evapouration - the process by which liquid water is transformed into water vapour. A large amount of energy is required, and this is usually provided by heat or by the movement of air.

Sublimation - when ice sheets, glaciers and snow fields release water by the direct change of state from a solid to a gas without passing through the liquid stage.

Transpiration - the process by which water is lost from a plant through the stomata in its leaves.

Evapotranspiration - the total amount of moisture removed by evapouration and transpiration from a vegetated land surface.

Condensation - the process by which droplets of water or ice are formed when water vapour is cooled to dew point. During the process, latent heat of condensation is released. 

Ablation - the melting of ice, mainly during summer months, and usually at the snout end of the glacier.

Precipitation  - water in any form which falls from the atmosphere to the surface of the earth. It includes rainfall, snow, sleet and hail.

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Process in Hydrological System 2

Interception - the process by which raindrops are prevented from falling directly on to the soil surface by the presence of a layer of vegetation. 

Overland Flow - when the outcome of rainfall intensity on a slope is greater than the rate at which the water can infiltrate into the soil. A thin layer of water forms on the surface and it begins to move downslope under gravity.

Infiltration - the passage of water into the soil. Water is drawn into the soil by gravity and capillary action. As the soil becomes more saturated, the infiltration rate falls steadily.

Throughflow - the transfer of water from the soil storage zone to a channel at a much slower rate than overland flow.

Percolation - the downward vertical movement of water within a soil. The water then enters a groundwater store. Rate depends on the size of pores that the water travels through.

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Processes in Hydrological System 3

Groundwater Store - water that collects underground in the pore spaces in the soil and rock.

Groundwater Flow - water fills all the spaces available so the rock or soil is saturated. The water can then be transferred slowly through rock and into the bed of the river.

Runoff - all the water that enters a river and flows out of the drainage basin. Overland flow, through flow and groundwater flow all contribute to this. 

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The Water Balance

This is the balance between inputs into a drainage basin and outputs. Water Balance equation-

Precipitation (P) = Evapotranspiration (E) + Streamflow (Q) +/- Storage

Water Surplus - occurs when precipitation is greater than evapotranspiration and streamflow. This will create saturated soil. Water surplus occurs from December to May.

Water Deficit - occurs when precipitation is less than evapotranspiration and streamflow. This will create dry soil.

Soil Moisture Utilisation - when plants and animals are using the soil for processes such as transpiration and evapotranspiration.

Field Capacity Attained - precipitation is greater then evapotranspiration, Since September, the store of water in the soil has been 'recharging' -soil is completely saturated.

Soil Moisture Recharge - water is replaced using overland flow following utilisation in the summer,

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Carbon Cycle Stores

The carbon cycle has stores (known as sinks or pools) in rocks, sea floor sediments, oceans, the atmosphere and biosphere. Sedimentary rocks hold 99.9% of all carbon on the Earth. The sizes of the various stores are:

  • Atmosphere 600Gt
  • Ocean Surface 700Gt
  • Ocean Deep Layer 38000Gt
  • Soil 2300Gt
  • Terrestrial Biomass 560Gt
  • Fossil Fuels 4130Gt
  • Sedimentary Rocks 60,000,000-100,000,000 Gt

Gt= Gigatonnes 1Gt= 1 billion tonnes 

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Sub-Systems of Carbon Cycle

Terrestrial 'fast' Carbon Cycle - this relates to the uptake of CO2 from the atmosphere by plants during photosynthesis. CO2 is released back into the atmosphere during plant and animal respiration. CO2 and Methane are released back during the decomposition of organic matter. The cycling of Carbon between the soil, vegetation and atmosphere is relatively rapid.

Oceanic Carbon Cycle - Carbon is held in a dissolved form in the water of the ocean and in the tissues of oceanic organisms. Inputs and outputs to this cycle take place through gas exchange with the atmosphere and through an input of organic carbon and carbonate ions from continental runoff. Because of the size of the oceanic carbon store, small changes in carbon cycling have global impacts. Ocean sediments are an important long-term Carbon store.

FAST CYCLES

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Sub-Systems of Carbon Cycle 2

Atmospheric Carbon Cycle - Atmospheric Carbon occurs as CO2 and Methane. Methane is a more powerful greenhouse gas but is short- lived in the atmosphere, CO2 is removed from the atmosphere through interactions with the terrestrial and oceanic carbon cycles, e.g. photosynthesis and water absorption.

Slow Carbon Cycle - The 'slow' cycle refers to the cycling of Carbon between rock stores, the atmosphere and oceans through processes of weathering over millions of years. Weathering of rocks on continents creates a net carbon sink in the oceans. Chemical weathering by rocks through carbonic acid produces carbonate run off, which is transferred to the oceans. Here, organisms use it to create shells; when the organisms die the carbonate sediment produced eventually forms limestone. This long-term Carbon store is released to the atmosphere through volcanic activity.

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Cloud Formation

Clouds are visible masses of water droplets or ice crystals held in the atmosphere, they form when:

  • air is saturated either because it has cooled below dew point or evaporation means the air has reached its maximum water-holding capacity.
  • condensation nuclei are present.

The greater the amount of moisture in the cooling air, the greater the condensation and cloud formation.

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Causes of Precipitation

Condensation that is a direct cause of precipitation can occur when:

1. air temperature is reduced to dew point, e.g. warm moist air passes over a cold surface on a clear night or heat is radiated out into the atmosphere and the ground gets colder, cooling the air above it.

2. the volume of air increases as it rises and expands but there is no addition of heat (abiatic cooling). In this example, the air may be forced to rise for three different reasons, each resulting in precipitation:

  • air is forced to rise over hills and mountains producing orographic rainfall.
  • air masses of different temperatures and densities meet; the warm air rises over the cool sinking air and results in frontal rainfall.
  • warm air rises from hot surface on a sunny day causing convectional rainfall.
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Processes in Carbon Cycle 1

Precipitation - atmospheric CO2 dissolves in rainwater to form weak carbonic acid. Rising concentrations of CO2 in the atmosphere resulting from anthropogenic emissions have increased the acidity of rainfall and ocean surface waters.

Photosynthesis - plants use energy from sunlight and combine CO2 from the atmosphere from the soil to form carbohydrates. Carbon is stored for long periods of time- trees live long time and take long time to decompose.

Respiration - plants release CO2 back into the atmosphere through respiration. Soil respiration- microscopic organisms in soil respire.

Decomposition - this process by fungi and bacteria releases CO2 into the atmosphere. It also produces soluble organic compounds dissolved in run-off from land surface.

Combustion - fossil fuels contain carbon captured by living organisms over periods of millions of years and stored in the earth's crust. The fuels are mined and combusted, forming CO2.

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Processes in Carbon Cycle 2

Carbon Sequestration - CO2 moves from the atmosphere to the ocean by the process of diffusion. At low latitudes, warm water absorbs CO2. At high latitudes where cold water sinks, the carbon is transferred deep into the ocean. Where the cold water returns to the surface and warms again, it loses CO2 to the atmosphere; in this way CO2 is in constant exchange between the oceans and the atmosphere. This vertical circulation is a process called the oceanic carbon pump. Phytoplankton also fix CO2 through photosynthesis, and the carbon passes through the oceanic food web. When organisms die the shells sink into deep water; the decay of marine organisms releases some CO2 into deep water (the biological pump). Some material forms layers of carbon-rich sediments which over millions of years turns into sedimentary rocks.

Weathering - breaks down rocks on the Earth's surface. Large particles deposited on shore; sediment accumulates; layers build; surface pressure; shale rocks formed. Within the ocean, dissolved sediments mix with the seawater and are used by marine organisms to make skeletons and shells containing CaCO3. When these organisms dies the carbonate collects and sinks and sedimentary rocks form.

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Land Use Change 1

Urbanisation - 

  • Natural surfaces; vegetation and soil replacedby impermeable concrete, brick tarmac surfaces.
  • Infiltration reduced.
  • Urban drainage systems remove surface water rapidly, e.g. gutters.
  • Water levels of rivers rise rapidly owing to quick transfer of surface water.
  • In particular, urban development on floodplains reduces water storage capacity and leads to increased river flow and flooding.
  • Urban growth reduces the amount of surface vegetation.
  • CO2 emissions from energy consumption, transport and industry increase.
  • Increase in CO2 emissions from cement manufacture.
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Land Use Change 2

Forestry-

  • Plantations of natural forest increase interception of rainfall, e.g. conifers which are evergreen and planted at high density.
  • Evaporation increases as leaf store water evaporates directly back to the atmosphere.
  • Run-off and stream discharge is reduced. 
  • Transpiration in forested areas is higher than for farmland and moorland.
  • Localised deforestation means that evapotranspiration is lower as new minimal vegetation cover has fewer leaves and fewer roots; there is less interception because of reduced canopy, overland flow and throughflow increase, increased river discharge and risk of localised flooding.
  • Changing land use to forestry increases carbon stores,
  • Forest trees extract CO2 from the atmosphere and sequester it for 100s of years- carbon stored in wood of the tree stem.
  • Forest trees are only an active carbon sink for the first 100 years after planting and so forestry plantations have a rotation of 80-100 years.
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Land Use Change 3

Farming Practices-

  • Irrigation diverts water from rivers and groundwater supplies to cultivated land. Some of this water is used by plants from soil storage and released by transpiration.
  • Interception, evaporation and transpiration are all lower in agroecosystems than in forest and grassland ecosystems.
  • Ploughing increases soil moisture loss and can form drainage channels which increase run-off and lead to soil erosion.
  • Underground drainage channels in farmland increase water transfers to rivers.
  • Use of heavy machinery can compact the soil and increase run-off.
  • Clearance of forest from farming reduces above and below-ground carbon stores.
  • Ploughing reduces soil carbon storage and exposes soil organic matter to oxidation.
  • Harvesting means that only small amounts of organic matter are returned to the soil, further reducing carbon stores.
  • Rice paddies generate methane.
  • Livestock releases methane gas as a by-product of digestion.
  • Emissions from tractors increase CO2.
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Land Use Change 4

Water Extraction-

  • It is the process of taking water from a surface or ground source either temporarily or permanently.
  • Uses can be agricultural, industrial or domestic.
  • Hydrogeology is used to monitor safe levels of water extraction as over-extraction can lead to several issues such as: rivers drying up, damage to wetland ecosystems, sinking water tables and empty wells.
  • In coastal areas, intrustion of salt water from the sea degrades groundwater and leads to difficulties of usage for different purposes.
  • Aquifers: water-bearing rocks include chalk and sandstone. Groundwater is abstracted for use by wells and boreholes. The border between saturated and dry rock is the water table and this fluctuates according to season and amount of water abstraction.
  • Artesian Basins: sedimentary rocks may form a basin shape or 'synacline'; an aquifer trapped between impermeable rock layers that may contain groundwater which is under artesian pressure. A well could allow the water to flow to the surface.
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Fossil Fuel Combustion

There remains a high global dependency on fossil fuels (coal, oil and gas). Approximately 10 billion tonnes of CO2 are released into the atmosphere anually. Anthropogenic carbon emissions impact significantly on the carbon stores of the atmosphere, oceans and biosphere. Combustion of fossil fuels and the resulting transfer of carbon from geological stores to the atmosphere and oceans is the main cause of global warming. One possible solution is carbon capture and storage (CCS). However, this is limited by high capital costs and by the fact that the process uses large amounts of energy and requires storage reservoirs with specific geographical conditions.

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Positive and Negative Feedback

Feedback is a natural response to a change in a system's equilibrium. The feedback can be positive (when the initial change causes further change) or negative (the system change is countered and equilibrium is restored). Sometimes, on factor can induce both positive and negative feedback, e.g. atmospheric water vapour. 

POSITIVE FEEDBACK IN WATER CYCLE - surface temperature increases slightly> increased evaporation from the oceans>  more water vapour in the atmosphere> increased greenhouse effect > surface temperature increases...>

NEGATIVE FEEDBACK IN WATER CYCLE - surface temperature increases slightly> increased evaporation from the oceans> more low clouds in the atmosphere> reflects more sunlight back into space> surface temperature reduces. 

POSITIVE FEEDBACK IN CARBON CYCLE - global warming will intensify carbon cycle> speed up decomposition> release more CO2 into atmosphere> amplyfying greenhouse effect.

NEGATIVE FEEDBACK IN CARBON CYCLE - global warming> more CO2> stimulates photosynthesis> carbon fertilisation occurs> excess CO2 extracted from atmosphere and store in biosphere> eventually carbon would end up in long-term storage in soils and ocean sediments> restortation of equilibrium.

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Variations in the Cycle Pathways over Time

There is close monitoring on climate change and the potential damage it could cause through satellite technology and remote sensing of global air temperatures, sea surface temperatures, sea ice thickness and rates of deforestation

Short Term Changes:

  • Diurnal Changes= occurs within 24 hours (water cycle). Evaporation and transpiration are both much lower at night as temperatures drop. Downpours in the afternoon because of intense convectional heating are a feature of some global climates. Carbon flows from the atmosphere to vegetation during the day; the flux is reversed at night. Low levels of sunlight reduce photosynthesis in vegetation on land and in phytoplankton in oceans.
  • Seasonal Changes= seasons are controlled by variations in the intensity of solar radiation. This has an impact on rates of evapotranspiration and precipitation which impact the water cycle. Seasonal variations in the carbon cycle are shown in month-to-month variations in net primary productivity (NPP). In summer months in the northern hemisphere, there is a net flow of CO2 from the atmosphere to the biosphere as vegetation is in full foliage so photosynthesis is rapid.
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Long-Term Changes

Over the last 1 million years the global climate has been unstable, with large fluctuations in temperatures occuring at regular intervals . In the past 400,000 years, there have been four major glacial cycles, with cold glacials followed by warmer inter-glacials. 

Impacts of Glacials on Water Cycle: sea levels fall, ice sheets and glaciers expand, ice sheet advance destroys forest and grassland, water stored in biosphere shrinks, evapotranspiration declines, water cycle slows due to reduction in evapotranspiration and water storage.

Impacts of Glacials on Carbon Cycle:  less CO2 in the atmosphere. Changes in oceanic circulation bring nutrients to the surface; phytoplankton grows rapidly and fixes CO2 in photosynthesis; when phytoplankton die the carbon is stored deep in the ocean. Less exchange of carbon between the soil and the atmosphere due to ice coverage. Because of the increase in ice coverage there is less vegetation and a reduction in the carbon fixed by photosynthesis. 

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Importance of Research and Monitoring

  • Cycling of carbon and water are central to supporting life on Earth and an understanding of these cycles and how they are changing is central to managing global challenges such as the impacts of climate change and consequences for future water, food and energy supply.
  • Changes in the water and carbon cycles are central to analysis of environmental change and the global challenges presented. 
  • Understanding of regional variations in the sources and sinks of CO2 helps identify sequestration and emission management options.
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Links and Interdependence of the Cycles

The water and carbon cycles interact directly where carbon is transported, dissolved or suspended in running water. Transport of weathering products and organic matter from the continents to the oceans is an important aspect of carbon cycling which is directly linked to water flux. Similarly, the impact of the changing atmospheric carbon concentrations on global climate has a profound effect on water cycling, impacting terrestrial and oceanic evaporation and patterns of precipitation. 

The two cycles are also linked through the role of ecosystems in carbon cycling since moisture availability is a key control on plant distribution and plant life plays a key role in terrestrial carbon cycling. 

Climate change and land-use change may lead to significant change in the functioning of terrestrial ecosystems which impact both water and carbon cycling.

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Interlinkages

Atmosphere - atmospheric CO2 has a greenhouse effect. CO2 is involved in photosynthesis by terrestrial plants + phytoplankton. Plants, which are store carbon, extract water from the soil and transpire it as part of the water cycle. Water is evaporated from the oceans to the atmosphere, + CO2 is exchanged between the two stores.

Oceans - ocean acidity increased when exchanges of CO2 are not in balance (i.e. inputs to the oceans from the atmosphere exceed outputs). The solubility of CO2 in the oceans increases lower sea-surface temperatures (SSTs). Atmospheric CO2 levels influence: SSTs + thermal expansion of oceans; air temperatures; the melting of ice sheets + glaciers; + sea level.

Vegetation and Soil - water availability influences rates of photosynthesis, NPP, inputs of organic litter to soils + transpiration. The water storage capacity increases with organic content. Temperatures + rainfall affect decomposition rates + release of CO2 into the atmosphere.

Cryosphere - CO2 levels in atmosphere determine the intensity of the greenhouse effect+melting of ice sheets, glaciers e.t.c. Melting exposes land + sea surfaces which absorb more solar radiation and increase temperatures. Permafrost melting exposes organic material to oxidation + decomposition which releases CO2 and CH4. Run-off, river flow+evaporation respond to temperature change.

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Human Activities Causing Change

  • Rising demand for water for irrigation, industrial and domestic usage has created water shortages in many areas across the globe, such as Bangladesh. India and the Colorado Basin in the USA.
  • Increased soil erosion (due to deforestation and poor agricultural practices) is leading to a decline in the carbon store in soil.
  • Urbanisation reduces evapotranspiration that would naturally occur from vegetation; as a result, precipitation can decline. Urban areas also increase run-off and reduce infiltration which can lower water tables.
  • Fossil fuels account for 87% of global primary energy consumption. This has removed billions of tonnes of carbon from geological stores,
  • Acidification of the oceans threatens the biological carbon stores of oceans and the carbon fixed by the process of photosynthesis in phytoplankton.
  • Deforestation reduces the carbon store in the biosphere and the carbon fixed by photosynthesis.
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Impact of Long-Term Climate Change 1

Water Cycle:

  • Global warming has increased the amount of evaporation and thereby the amount of water vapour in the atmosphere. The positive feedback of water vapour- a greenhouse gas- further increases global temperatures, evaporation and precipitation.
  • Increased precipitation in areas where there is urbanisation, building on floodplains and deforestation will increase flood risks.
  • Water vapour is a source of energy in the atmosphere which can lead to more extreme weather events, e.g. storms and tornadoes.
  • Water stored in the cryosphere will shrink as global warming increases melting of glaciers and will be transferred into oceans.
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Impact of Long-Term Climate Change 2

Carbon Cycle-

  • Impacts are more complex, but the long-term impact of climate change will probably be an increase in the carbon stored in the atmosphere, a decrease in the carbon stored in the biosphere and the oceans.
  • Higher temperatures increase rates of decomposition, and the rate of carbon transfer from the biosphere and soil to the atmosphere will increase.
  • Where temperatures are so high the aridity increases, forests will be replaced by grasslands which reduces the carbon store in woody vegetation.
  • Global warming may allow boreal forests to spread north.
  • In permafrost areas carbon is being released from frozen ground as temperatures rise.
  • Ocean acidification (caused by CO2 dissolving in the oceans and creating carbonic acid) is limiting the capacity of oceans to store carbon.
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Global Management Strategies for Carbon Cycle

Afforestation - this is planting trees in areas where deforestation as taken place or new areas. Trees act as an important carbon sink and so they can reduce atmospheric CO2 and reduce flood risks and soil erosion. The UN's Reducing Emissions from Deforestation and Forest Degredation (REDD) schemes encourage developing countries to conserve their forests.

Wetland Restriction - wetlands account for 35% of the terrestrial carbon pool and include marshes, peatlands, floodplains and melgroves. They form important carbon sinks and protection schemes include International Convention on Wetlands and the European Union Habitats Directive. Restoration at a local level involves raising water tables to create waterlogged conditions. Water levels can be maintained also by diverting drainage ditches and installing sluice gates.

Improved Agricultural Practices - mulching adds organic matter and prevent carbon losses from the system. Rotation of cash crops with cover crops can increase the biomass returned to the soil. Imporved crop varieties can increase productivity and enhance soil organic carbon (SOC).

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Global Management Strategies for Carbon Cycle 2

Reducing Emissions - 

  • Carbon Trading - businesses can be allocated a quota for CO2 emissions; carbon credits are recieved for emissions lower than the quota and the financial penalties or the opportunity to purchase additional credits are the consequences of exceeding for the quota. Carbon offsets are credits to countries and businesses for schemes such as afforestation and renewable energy.
  • International Agreements -  reaching consensus and action from all countries is complex and frequently affected by self interests of different countries. The only significant global agreement has been the Kyoto Protocol (1997) where most ACs agreed legally binding reductions on CO2 emissions. Even so, India and China were exempt and the USA did not ratify the agreement. After Kyoto expired in 2012, a new agreement was reached in the Paris Climate Convention 2015 for implentation in 2020. Countries set their own voluntary targets which aren't legally binding.
  • Transport Innovations - road transport initiatives include sustainable transport schemes, congestion charging (London), park and ride schemes (Cambridge) and integrated transport networks (Curitiba, Brazil); there is a range of mitigation strategies in the aviation industry, e.g. adopting fuel-efficient routes and cruising at a lower speed.
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Global Management Strategies for Water Cycle

  • Forestry - trees impact on many processes of the water cycle, e.g. interception, infiltration. The important role of forests in the functioning of the global water cycle is recognised internationally by projects such as the UN's Reducing Emissions from Deforestation and Forest Degredation (REDD) scheme and the World Bank's Forest Carbon Partnership Facility (FCPF) which fund many projects in Africa, Asia and South America.
  • Drainage Basin Planning - aims; surface storage (restoring wetlands), run-off (reduce artificial drainage in urban areas, permeable surfaces in urban areas, afforestation projects), groundwater storage (limiting abstraction of water, limiting artificial recharge). EU's Directive Framework= 10 river basins identified in England and Wales, each district has its own River Basin Management Plan, set targets on groundwater levels, water quality and abstraction rates.
  • Water Allocations - agriculture is the biggest consumer- 90% of consumption globally. Wastage of water through evaporation and over-irrigating crops. Better Management; better water harvesting (storage in reservoirs and ponds), recovering and recyclong of water waste. Improving Management Strategies; minimising water loss from evaporation (zero soil disturbance, mulching, drip irrigation),
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