The Carbon Cycle

• Hydroelectric dams harness the kinetic energy of falling water to produce electricity.
• Slow carbon cycles are where Earth tries to keep the balance stable. This happens over millions of years.

  For example, the Himalayan Mountains are slowly pushed up and weathered away.
• Fast carbon cycles involve the ongoing flow of carbon between the land, atmosphere and oceans.

  Carbon is measured in petagrams (1 petagram = 1 billion tonnes).
• 𝘾𝘼𝙍𝘽𝙊𝙉 𝘾𝙔𝘾𝙇𝙀𝙎:

  • fast = flows, transfer
  • slow = storage
• 𝙁𝘼𝘾𝙏𝙊𝙍𝙎 𝘼𝙁𝙁𝙀𝘾𝙏𝙄𝙉𝙂 𝙏𝙃𝙀 𝙁𝘼𝙎𝙏 𝘾𝘼𝙍𝘽𝙊𝙉 𝘾𝙔𝘾𝙇𝙀:

  • photosynthesis
  • respiration
  • combustion
  • decomposition
• Examples of combustion include slash and burn agriculture, burning fossil fuels, wildfires, hydrocarbon fuel extraction.
• Wildfires are a problem because forests are considered to be carbon sinks, and trees store a lot of carbon. This carbon is released through combustion.

  Each year, 3-4 million km2 of Earth's land is burned by wildfires.
• Older trees are more susceptible to wildfires, however also store a lot more carbon than younger trees.
• When a wildfire occurs, the ability of photosynthesis to take place is removed because the vegetation is burnt.
• A benefit of wildfires is that the diversity of plant species increases when a decrease in dominant species reduces competition.

  However, the species diversity initially reduces everywhere and is difficult to artificially replant.
• The organisms that make up fossil fuels are 650 million years old.
• 21 petagrams of carbon are released into the atmosphere every year from the burning of fossil fuels.
• Carbon dioxide is responsible for 60% of the radiative forcing caused by greenhouse gases.
• There has been a 40% increase in carbon in the atmosphere since the Industrial Revolution in 1750.
• Greenhouse gas emissions exceeded pre-industrial levels in 2011.
• 40% of human-emitted carbon dioxide isn't removed by carbon sinks.
• 2013 witnessed a 150% increase in CO2 levels since the Industrial Revolution.
• Carbon dioxide emissions are now 54% above the 1990 level.
• A 'fire break' involves clearing trees to prevent wildfire spread.
• As the global temperature rises the frequency of droughts also rises, which leads to drier land. The severity of storms and lightning also increases, as well as high temperatures, both of which increase the likelihood of dry vegetation catching fire.
• 𝙁𝘼𝘾𝙏𝙊𝙍𝙎 𝘿𝙍𝙄𝙑𝙄𝙉𝙂 𝘾𝙃𝘼𝙉𝙂𝙀 𝙄𝙉 𝙏𝙃𝙀 𝙈𝘼𝙂𝙉𝙄𝙏𝙐𝘿𝙀 𝙊𝙁 𝘾𝘼𝙍𝘽𝙊𝙉 𝙎𝙏𝙊𝙍𝙀𝙎:

  • weathering
  • carbon sequestration in oceans
  • volcanic activity
  • diffusion
• Weathering involves the breakdown and decay of rocks in their original place close to the surface. They can be dissolved by mildly acidic rainwater that has absorbed CO2. The carbon in the rocks is held in solution and is transported via the water cycle to the ocean.
• Volcanic activity returns carbon to the atmosphere that has been trapped in deep rocks for millions of years. Volcanoes emit between 130 and 380 million tonnes of CO2 a year. Further, lava contributes to weathering processes and converts CO2 in the air into carbonates in solution.
• Carbon sequestration in oceans involves the transfer of carbon from the atmosphere to plants/soils/rock formations/oceans. It is a process of trapping carbon, for example when in the ocean shell-building animals use it for growth.
• Diffusion of CO₂ into the oceans occurs as CO₂ dissolves into and out of the ocean surface water. The rate of diffusion is controlled by the wind currents and temperatures.
• Oceanic carbon pumps are the movement of carbon from the atmosphere to the ocean, leading to the vertical mixing in the ocean layers. Warm water in surface currents is carried from the warm tropics to the cold polar region, where it is cooled to be dense enough to sink. Cold water rises to the surface and warms, losing CO₂ to the atmosphere (vertical circulation - ensuring carbon is in constant transfer).
• Biological carbon pumps in the ocean are living things moving carbon from the atmosphere into surface waters, deeper and into rocks such as limestone, which trap carbon for millions of years. For instance, blooms of phytoplankton at the surface photosynthesising.
• The carbon budget is the difference between the inputs of carbon into a subsystem and the outputs of carbon from it.
• A carbon sink is an area where the carbon intake is greater than the output (e.g. forests, oceans).
• A carbon source is an area which gives out more carbon than it takes in.
• The Spearman's Rank correlation coefficient tests the relationship between variables.
• A null hypothesis predicts no relationship between variables.
• An alternate hypothesis predicts there will be a relationship between variables.
• The Spearman's Rank (rₛ) equation:

  • Σ = the sum of
  • D = the difference between ranks
  • n = the nu

  A) 1

  B) 2

  C) n

  
• The Spearman's Rank equation gives us a number between -1 and 1. The greater the number the stronger the relationship.
• It is a general aim to be 95% sure of a Spearman's Rank outcome. Therefore, the 0.05 column of the critical value table - in the appropriate row for the number of data pieces - shows us the certainty.
• 𝙧ₛ 𝘾𝙊𝙉𝘾𝙇𝙐𝙎𝙄𝙊𝙉 𝙀𝙓𝘼𝙈𝙋𝙇𝙀:

  Our calculated value of R was 0.840. The critical value of R when n = 12 is 0.503 (at the 5% significance level). Therefore, our calculated value of R is greater than the critical value, so we can reject the null hypothesis and accept the alternate hypothesis. We are 95% certain that fossil fuel emissions increase global atmospheric carbon.
• 𝙇𝘼𝙉𝘿 𝙐𝙎𝙀 𝘾𝙃𝘼𝙉𝙂𝙀:

  • the conversion to agriculture/pasture land and farming practices
  • the conversion to shifting cultivation
  • abandoning agricultural/pastoral land
  • tree plantations (afforestation)
• 𝟭. 𝗖𝗢𝗡𝗩𝗘𝗥𝗦𝗜𝗢𝗡 𝗧𝗢 𝗔𝗚𝗥𝗜𝗖𝗨𝗟𝗧𝗨𝗥𝗘:

  • Sheep can damage soil structure (soil is an important carbon store).
  • Crops have a yearly growth cycle and are short-term stores of carbon.
  • Soil is blown/washed away when crops are harvested.
• 𝟮. 𝗙𝗔𝗥𝗠𝗜𝗡𝗚 𝗣𝗥𝗔𝗖𝗧𝗜𝗖𝗘𝗦:

  • When crops are harvested all nutrients are removed from the soil.
  • Crops are immediately replaced and the 'litter' phase of the nutrient is skipped; no nutrients are returned to the soil.
  • Fertilisers and pesticides damage soil.
  • Cattle farming.
  • Slash and burn.
  • Rice paddies feed 1/2 the population of the world. They are grown in water and decomposed material in the water evaporates, releasing methane.