ELSS

• Global management strategies - carbon cycle

  • Wetland restoration
  • Afforestation
  • Agricultural practices
  • International agreements
  • Cap and trade
• Wetland restoration

  • Contain 35% of terrestrial carbon pool
  • Destruction of wetlands causes loss of biodiversity and wildlife habitats, and the transfer of CO2 and CH4 to the atmosphere
  • Wetlands store on average 3.25 tonnes carbon / ha / yr
  • Restoration focuses on raising local water tables to recreate waterlogged conditions
• Afforestation

  • Trees are carbon sinks, so afforestation can reduce atmospheric CO2 levels in the medium to long term, and combat climate change
  • It also reduces flood risks and soil erosion, and increases biodiversity
  • China aims to afforest 400,000 km2 by 2050 (started in 1978)
• Agricultural practices

  • Overcultivation and overgrazing leads to soil erosion and the release of carbon to the atmosphere
  • Intensive livestock farming produces 100 million tonnes / year of CH4
  • Zero tillage - growing crops without ploughing the soil reduces the risk of erosion by wind and water
  • Crop residues - leaving stems and leaves on fields after harvest provides ground cover and protection against soil erosion
  • Improving the quality of animal feed so less feed is converted to CH4 (mixing methane inhibitors with it)
• International agreements

  • Paris Climate Agreement aims to reduce global CO2 emissions below 60% of 2010 levels by 2050
  • Agreements are not legally binding, there are no sanctions for not sticking to them, and there is no timetable for implementing them meaning that progress will be slow
  • However, rich countries transfer funds and technologies to assist poorer countries, supporting international relations
• Cap and trade

  • Businesses are allocated an annual quota for their CO2 emissions
  • If they emit less than their quota they receive carbon credits which can be traded on international markets
  • If they emit more than their quota they must purchase additional credits or incur financial penalties
• Global management strategies - water cycle

  • Forestry
  • Water allocations
  • Drainage basin planning
• Forestry

  • Forests are important in the global water cycle because they stabilise the regional water cycle and protect against floods by intercepting precipitation, allowing up to 30% of the water to evaporate back into the atmosphere directly from the canopy without reaching the ground
  • Brazil has received support from the UN and WWF to protect its forests
  • The Amazon Regional Protected Areas programme now covers nearly 128 million acres of the Amazon Basin
  • There is more evaporation because intercepted rainfall sits on leaf surfaces
  • Less run-off due to more interception
• Water allocations

  • In countries of water scarcity, governments allocate water resources
  • Agriculture is the biggest consumer (70% of water withdrawals and 93% of consumption)
  • Wastage of water occurs through evaporation and over-irrigating crops
  • Mulching, zero soil disturbance and drip irrigation reduce water loss by evaporation
• Importance of water

  • Allows organic molecules to mix and form more complex structures
  • Oceans absorb heat, store it and release it slowly
  • Clouds reflect around a fifth of incoming solar radiation
  • Water vapour is a greenhouse gas and absorbs long-wave radiation from the Earth maintaining temperatures almost 15 degrees higher than they would be otherwise
  • Plants - photosynthesis, respiration, transpiration, maintain rigidity and to transport mineral nutrients from the soil
  • People and animals - chemical reactions
  • Used economically for electricity generation, crop irrigation and food manufacturing
• Importance of carbon

  • Stord in carbonate rocks such as limestone, sea floor sediments, ocean water, the atmosphere and the biosphere
  • Life is carbon-based (carbon is in large molecules such as proteins, carbohydrates and nucleic acids)
  • Fossil fuels such as coal, oil and natural gas power the global economy
  • Oil is used in the manufacture of plastics, paint and synthetic fabrics
  • Agricultural crops and forest trees store carbon as food, timber, paper and textiles
• Water stores

  • Oceans 97%
  • Polar ice and glaciers 2%
  • Groundwater, lakes, soils, atmosphere, rivers and biosphere smaller proportions
• Water inputs and outputs

  • Inputs to the atmosphere - water vapour evaporated from oceans, soils, lakes and rivers, and transpired through leaves (evapotranspiration)
  • Outputs from atmosphere - precipitation and condensation (fog), ice sheets release water by ablation (melting and sublimation)
  • Outputs from groundwater - precipitation and meltwater drain as runoff into rivers which flow into oceans or inland basins
  • Inputs into soil - precipitation infiltrates so water under gravity percolates into permeable rocks or aquifers, and groundwater reaches surface as springs or seepages for runoff
• Carbon stores

  • Atmosphere 600 billion tonnes
  • Oceans 38,700 billion tonnes
  • Sedimentary (carbonate) rocks 60,000-100,000 billion tonnes
  • Sea floor sediments, fossil fuels, land plants and soil/peat smaller proportions
• Carbon inputs and outputs (slow carbon cycle)

  • Carbon stored in rocks, sea-floor sediments and fossil fuels is locked away for millions of years
  • 10-100 million tonnes of carbon circulated a year
  • CO2 diffuses from atmosphere into oceans where clams and corals make their shells and skeletons by forming calcium carbonate
  • On death, these organisms sink to the ocean floor, and are converted to carbon-rich sedimentary rocks due to heat and pressure
  • Carbon held in rocks for 150 million years, and are then vented to the atmosphere in volcanic eruptions, or chemical weathering occurs to atmosphere
• Carbon inputs and outputs (fast carbon cycle)

  • Carbon circulates quickly between atmosphere, oceans, biosphere and soils
  • 10-1000 times faster than transfers in slow carbon cycle
  • Phytoplankton and land plants absorb CO2 from atmosphere and combine it with water to make glucose and oxygen through photosynthesis (important in food chain), respiration is the opposite
  • Decomposition of dead organic material by microbial activity returns CO2 to the atmosphere
  • Atmospheric CO2 dissolves in ocean surface waters, oceans ventilate CO2 back to the atmosphere
  • Carbon stored in oceans for 350 years
• Water balance equation

  • Precipitation = evapotranspiration + streamflow +/- storage
• Precipitation

  • Rain, snow, hail etc.
  • Vapour in atmosphere cools to its dew point and condenses into tiny water droplets or ice particles to form clouds
  • Droplets aggregate, reach a critical size and leave the cloud as precipitation
  • Precipitation impacts water cycle at drainage basin cycle
  • Rain reaches the ground and flows into rivers, but at high latitudes it is snow so remains on the ground for several months (time lag between snowfall and runoff)
  • Intensity is the amount of precipitation falling in a given time, high intensity moves overland because the rate exceeds infiltration capacity
• Transpiration

  • Diffusion of water vapour to the atmosphere from the stomata of plants
  • Responsible for around 10% of moisture in the atmosphere
  • Influenced by temperature, wind speed and water availability to plants
• Condensation

  • Phase change of vapour to liquid water, when air is cooled to its dew point
  • At this critical temperature, air becomes saturated with vapour resulting in condensation
  • Clouds form through condensation in the atmosphere
• Formation of clouds

  • Water vapour cooled to its dew point
  • Air, warmed by contact with the ground of sea surface, rises freely through the atmosphere
  • As the air rises and pressure falls it cools by adiabatic expansion (vertical movement of air known as convection)
  • Air moves horizontally across a relatively cooler surface (known as advection)
  • Air masses rise as they cross a mountain barrier or as turbulence forces their ascent
  • A relatively warm air mass mixes with a cooler one
• Evaporation

  • Phase change of liquid water to vapour
  • Heat needed for it to occur as molecular bonds of water are broken
• Interception

  • Vegetation intercepts some precipitation, storing it on branches, leaves and stems
  • The moisture either evaporates (interception loss) or falls to the ground
  • Rainwater that is briefly intercepted before dripping to the ground is known as throughfall
  • A higher wind speed, trees with a larger surface area, and conifers cause more interception (conifers because they have leaves all year round, and water adheres to the spaces between the needles)
• Infiltration, throughflow, groundwater flow and runoff

  • Infiltration by gravity into soil and lateral movement, or throughflow to stream and river channels
  • Overland flow across the ground surface to stream and river channels
  • If soils are underlain by permeable rocks, water seeps or percolates deep underground, it moves slowly through the rock pores and joints as groundwater flow, and emerges at the surface as springs or seepages
• Ablation

  • Loss of ice from snow
  • A combination of melting, evaporation and sublimation
• Precipitation

  • Atmospheric CO2 dissolves in rainwater to form weak carbonic acid
  • Natural process
  • Rising CO2 concentration in the atmosphere has increased the acidity of rainfall, and ocean surface waters which could harm marine life
• Weathering

  • Most weathering involves rainwater which contains dissolved CO2 from the soil and the atmosphere
  • Limestone and chalk dissolved in carbonation, releases carbon to the rivers, oceans and atmosphere
  • Rainwater mixes with dead and decaying organic material in the soil to form acids which attack rock minerals (important in Amazon rainforest)
• Decomposition

  • Bacteria and fungi break down dead organic matter, extracting energy and releasing CO2 to the atmosphere, and mineral nutrients to the soil
  • Higher rates in warm, humid environments, but lower rates in cold environments
• Combustion

  • When organic material reacts or burns in the presence of oxygen, releasing CO2
• Carbon sequestration in oceans (physical inorganic pump)

  • Involves the mixing of surface and deep ocean waters by vertical currents, creating a more even distribution of carbon
  • CO2 enters the oceans from the atmosphere by diffusion, and the surface ocean currents transport the water and its dissolved CO2 pole-wards where it cools, becomes more dense and sinks
  • Deep ocean currents transport the carbon to areas of upwelling, where it rises to the surface and diffuses back into the atmosphere
• Carbon sequestration in oceans (biological organic pump)

  • Phytoplankton combine sunlight, water and dissolved CO2 to produce organic material
  • Carbon locked in phytoplankton accumulates in sediments on the ocean floor or is decomposed and released into the ocean as CO2
• Negative feedback in drainage basins and carbon cycle

  • Drainage basin - unusually heavy rainfall increases the amount of water stored in aquifers
  • Raises the water table, increasing flow from springs until water table reverts to normal levels
  • Carbon cycle - burning fossil fuels increases atmospheric CO2 and also stimulates photosynthesis
  • Negative feedback response should remove excess CO2 from atmosphere and restore equilibrium
• Aquifers

  • Permeable or porous water-bearing rocks such as chalk
  • Groundwater abstracted for public supply from aquifers by wells and boreholes
  • After emerging in springs and seepages, groundwater feeds rivers and makes a major contribution to their base flow
• Artesian basins

  • An aquifer confined between impermeable rock layers may contain groundwater which is under artesian pressure
  • If this groundwater is tapped by a well or borehole, water will flow to the surface under its own pressure
• In 2019, fossil fuels accounted for 84% of global energy consumption
• Fossil fuel consumption releases 10 billion tonnes of CO2 to the atmosphere annually
• Sequestration of waste carbon

  • Carbon capture and storage
  • CO2 separated from power station emissions
  • CO2 compressed and transported by pipeline to storage areas
  • CO2 injected into porous rocks deep underground where it is stored permanently
• Positive feedback in the water cycle

  • Higher temperatures cause more evaporation and so the atmosphere holds more water vapour
  • More cloud cover and precipitation is therefore caused
  • Positive feedback effect because water vapour is a greenhouse gas which absorbs long-wave radiation from the Earth, causing further rises in temperature
• Negative feedback in the water cycle

  • More atmospheric water vapour causes greater cloud cover which reflects more solar radiation back into space
  • As less solar radiation is absorbed by the atmosphere, oceans and land, global temperatures fall
• Positive feedback in the carbon cycle

  • Global warming intensifies the carbon cycle, speeding up decomposition and releasing more CO2 to the atmosphere, amplifying the greenhouse effect
  • In the Arctic tundra, as sea ice and snow cover shrinks, large expanses of sea and land are exposed, causing more sunlight to be absorbed, warming the tundra and melting the permafrost