Carbon Cycle and Greenhouse Effect

Where is Carbon found on Earth?

  • Sediments and rocks (fossilized material)
  • Ocean, atmosphere (stores inorganic carbon - dissolved carbon dioxide and hydrogen carbonate ions)
  • Soil (mixture of organic and inorganic)
  • Biomass (living things) can become fossilized or stored as oil
  • Methane - produced by decaying organic and inorganic material by methanogenic archaeans under anaerobic conditions
  • Peat - organic matter that isn’t fully decomposed (acidic/anaerobic conditions in waterlogged soils)

Fossils VS Oil

  • Oil, gas, and coal - come from partially decomposed organic matter
    • Oil and gas formed when this matter accumulated in porous rock
  • Fossils - animals such as reef-building corals and molluscs have hard parts that are composed of calcium carbonate
    • these become fossilized as limestone

How can carbon be released into the atmosphere?

  • Respiration
  • Methane
  • Combustion
  • Primarily responsible for recent increases of carbon in the atmosphere

The carbon cycle involves a few basic components:

  • synthesis of carbohydrates from atmospheric carbon dioxide and water (along with sunlight as the energy source) using photosynthesis (fixed carbon in organic compounds from inorganic compounds)
  • consumption of carbohydrates by both producers and consumers through the cellular respiration
  • waster products and dead plant and animal material are decomposed by decomposers
  • any animal and plant matter that isn’t decomposed can fossilize
  • through the combustion of oil natural gas and plant materials, stored carbon compounds are converted into carbon dioxide and water vapour
  • the carbon dioxide produced during this cycle is stored in the atmosphere and the oceans until used during photosynthesis

Source VS Sink

  • Carbon source - emits carbon
  • Carbon sink - receives/stores carbon

The Greenhouse Effect

  • natural process necessary for life as we know it
  • without a natural greenhouse effect, the earth would be 33 degrees (Celsius) colder
  • when energy from the sun enters the earth’s atmosphere, about a third of it is reflected back into space
  • most of the rest is absorbed by the surface of the earth
  • the earth emits this energy as long wave radiation/heat
  • greenhouse gases can absorb longwave radiation and retain it in the atmosphere
    • water vapour
    • carbon dioxide
    • methane
    • nitrogen oxides

Water vapour

  • transpiration
  • evaporation cellular respiration
  • fossil fuel combustion

Carbon dioxide

  • respiration
  • fossil fuel burning
  • decay of materials

Carbon dioxide is removed from the atmosphere by:

  • photosynthesis
  • absorption from ocean

Methane

  • present in smaller quantities than carbon dioxide, but more effective at trapping heat
  • produced from the decay of matter without the presence of oxygen
  • sources:
    • wetlands
    • rice paddies
    • animal digestive processes,
    • fossil fuel extraction
    • decaying garbage

Nitrous Oxide

  • soils and oceans

  • humans contribute through soil cultivation

  • use of fertilizers, nylon production

  • burning of organic material and fossil fuels

  • halocarbons - chemical compounds containing halogens

  • with low concentration but very effective at trapping greenhouse gases (ex. CFCs)

  • replaced with HFCs; safer for the ozone layer but still has a greenhouse effect

How has the atmosphere changed over time

  • ~3 billion years ago, the atmosphere was anoxic
  • anaerobic bacteria survived, died, and became sedimentary rock called stromatolites
  • photosynthesis evolved, used carbon dioxide and produced oxygen, this showed up as black iron oxide bands in stromatolites from 2.5-1.8 million years ago (after atmospheric oxygen increased)

How have humans affected the climate?

  • combustion of fossil fuels is putting more carbon into he atmosphere than can be naturally cycled
  • leading to increased greenhouse gases
  • by increasing the number of greenhouse gases humans have increased the amount of long-wave radiation trapped
  • changing land use:
    • replacing forests with farmland or asphalt increases energy reflected off the earth’s surface
    • also releases some stored carbon into the atmosphere and decreases the means of reabsorbing carbon (less photosynthesis)
  • atmospheric aerosols
    • industrial and agricultural activities are adding significant quantities of particles into the atmosphere

Impact

  • an average rise of only 4 degrees C would increase sea levels by 60cm
    • melting ice and thermal expansion of seawater
  • ice caps will disappear in the next century if rapid warming continues
  • disruption of ocean currents could lead to changing weather patterns
    • gulf stream slows, Britain and Europe could cool, heat is retained in the gulf of Mexico causing hurricanes
    • the greatest warming is predicted for Russia Canada and West Africa
  • dissolved carbon dioxide in oceans could threaten coral reefs
  • coral bleaching is caused by acid from increased carbon dioxide, the stress causes the coral to expel symbiotic algae, losing their colour and dying

Consequences of rising global temperatures on the arctic

  • increased rates of decomposition of detritus previously trapped in permafrost
  • expansion of the range of habitats of temperatures species
    • disrupt ecosystem
  • loss of ice habitat
  • changes in the distribution of prey species
    • affect higher trophic levels
  • increased success of pest species
  • political impacts