4. Atmosphere

• Atmospheric composition

  • Nitrogen 78.8%
  • Oxygen 20.95%
  • Argon 0.93%
  • Other gases including Xenon, Neon, Hydrogen, Helium, Krypton, Carbon dioxide
• Structure of the atmosphere

  1. Troposphere
  2. Tropopause
  3. Stratosphere
  4. Stratopause
  5. Mesosphere
  6. Mesopause
  7. Thermosphere
• Why does temperature fall with height in the troposphere

  Temperature falls as there are fewer molecules to absorb longwave radiation and distance increases from the surface of the earth, the source of longwave radiation
• Why does temperature rise with height in the stratosphere

  Ozone absorbs shortwave radiation from the sun, increasing temperatures
• Why does height fall with height in the mesosphere

  Atmosphere thins further so fewer molecules to absorb longwave radiation from the earths surface
• Why does temperature rise with height in the thermosphere

  Nearest to the sun so lots of incoming shortwave are absorbed by the few molecules that are present.
• Human impacts on the atmosphere

  • Enhancement of the greenhouse gas effect
  • Acid rain
  • Ozone depletion
  • Smog
• Fusion in the sun

  2 hydrogen = 2 helium + energy
• The electromagnetic spectrum 


  Gamma Rays, X-rays, Ultraviolet, visible light, infrared, radio waves

  • UV is damaging to living cells
  • Visible light is critical for plants in photosynthesis
  • Infrared is the most important energy source for heating the atmosphere
• Absorption of incoming solar radiation

  • Troposphere - Remaining uv and visable light either reflected or absorbed by earths surface; absorbed radiation is re-radiated as infrared energy
  • Stratosphere - Ozone in the stratosphere absorbs lots of uv radiation
  • Mesosphere - some visible light is reflected absorbed or scattered by molecules and clouds
  • Thermosphere - Incoming radiation in mainly uv and and visible light
• The stratosphere if heated by uv from the sun (due to high concentrations of ozone)
• The troposphere is heated by IR from the earth
• The greenhouse effect 


  Without the greenhouse effect the earth would have a mean temperature of -15 degrees C and not 15 degrees C which would be too cold for life to exist

  1. Incoming short-wave solar radiation is absorbed by the earths surface
  2. The earth re-radiates the energy as long wave
  3. Greenhouse gases in the atmosphere absorb about 25% of the outgoing long wave energy heating the atmosphere up
  4. 75% of the outgoing long-wave energy is transmitted into space
• Human sources of Greenhouse gases

  • Combustion of fossil fuels and deforestation (Carbon dioxide)
  • Aerosol propellants, refrigerants, fire extinguishers, foam plastics (Nitrogen oxides)
  • Reaction of atmospheric oxygen and nitrogen in high temps in engines and furnaces (nitrogen oxides)
  • Livestock, anaerobic digestion, landfill and paddy fields, both anaerobic decomposition and leaks from gas fields (methane)
  • Reaction of Nitrogen oxides produced from car engines with uv
• Changes in the oceans due to gcc

  • Changes to wind and current patterns
  • Sea level rise
  • Changes in the thermohaline circulation in the north atlantic
• Sea level rise 


  Caused by:

  • Addition of extra water to the oceans from melting land ice
  • Thermal expansion of the oceans as the water increase in temperature
• Changes in thermohaline currents

  • Cold, salty water is more dense, and therefore travels along the seabed
  • Increase precipitation and ice melting causes water to be less salty, disrupting thermohaline currents (e.g. the gulf stream)
• Changes in winds and currents

  • EL Nino events become more common
  • El Nino is when the cold up-welling ocean current off the coast of Peru (containing nutrients) ceases and the cold water is replaced by warm water flowing from the west
  • This effects the ecology and precipitation of areas around the globe
• Changes in the cryosphere

  • Reduced snow cover - amount and duration
  • Glaciers - changes in extent and speed of movement
  • Ice caps - changes to the thickness and movements
  • Ice shelves and land ice - changes to break up / movements
  • Sea ice - changes in thickness and area
• Albedo effect 


  Albedo is the fraction of solar energy (shortwave radiation) reflected from the earth back into space. Surfaces that are white are more reflective. Therefore, the smaller the cryosphere, the less energy is reflected, warming the planet
• Changes in Climate process

  Proportion of rain and snow - amount, duration, timing, location, direction, velocity
• Ecosystem 


  A community of organisms living in an area, their inter-relationships and interactions with their abiotic environment
• Photosynthesis 


  As temperature increase, the rate of photosynthesis also increases, the rate of growth in plants (and single celled organisms) increases, this leads to more plant biomass and therefore more potential food for herbivores, but also an increase in toxins
• Hibernation 


  A state of inactivity and a decreased metabolism in endotherms (warm blooded animals), to conserve energy during periods when food is unavailable. Hibernating species may benefit from being able to feed more of the year. Or may suffer as by being disturbed more frequently, or when food is unavailable
• Synchronicity 


  Species are often 'interdependent'. Climate change may lead to changes in the timings of ecological events. The survival interdependent species may be reduced. E.g. increased temperature cause means earlier flight for bees before flowering has occurred leaving no food
• Parasites and Disease 


  Warmer wetter climates often help spread parasites and disease. Leads to an increase in the range and breeding sites of vectors (often mosquitos). Increased cases of malaria, rift valley fever and many other (non-human) examples
• Habitats


  Abiotic conditions can change. e.g. Wetlands are strongly dependant on the water cycle. depending on their location, changes in precipitation will cause wetlands to grow or shrink.
• Species distribution 


  Species are adapted to their habitats. Species have a range of tolerances. Changes in abiotic and biotic factors cause a change in species distribution. Climate is changing rapidly, adaptation and evolution are often too slow. migration and colonisation to more suitable habitats.
• Species survival and extinction

  Climate change is leading to a decrease in survival rates for many species. This has and will lead to extinction. Climate change is associated with previous mass extinctions
• Species that are vulnerable to extinction

  • Small ranges
  • High latitudes
  • High elevations
  • Specialist species
  • Slow migrators/colonisers
  • Island species
• Positive feedback mechanisms 


  A situation where an initial change causes a reaction that increases the original change
• Positive feedback - Increased decomposition

  Increased temperatures -> Increased rate of anaerobic decomposition -> increased levels of atmospheric methane -> increased temp
• Positive feedback - Decreased albedo

  Increased temp -> decreased snow and ice -> Decreased albedo -> More shortwave radiation absorbed by earths surface -> more longwave radiation emitted by earth -> increased temp
• Positive feedback - Increased high level cloud 


  Increased temperature -> Increased evapotranspiration -> Increased high level cloud -> No change in shortwave radiation input to earths surface -> More longwave radiation trapped by cirrus clouds -> increased temps
• Positive feedback - release of methane 


  Increased temp -> Release of methane hydrates from sediment -> Increased levels of atmospheric methane -> Increased temp
• Positive feedback - Increased forest fires 


  Increased temps -> Drier peat soil -> Forest fires become more frequent and last longer -> Release of carbon dioxide in the atmosphere -> increased temps
• Negative feedback mechanisms 


  A situation where an initial change change causes a reaction that reduces the original change
• Negative feedback - Increased photosynthesis

  Increased temps -> Increased rate of photosynthesis -> Decreased levels of atmospheric carbon dioxide -> Temp returns to normal
• Negative feedback -> Increased low level cloud 


  Increased temp -> Increased evapo-transpiration -> Increased low level cloud -> Decreased shortwave input to the earths surface -> Temp returns to normal
• Limited historical data

  • Indirect sources (proxy data sources)
  • Some historic data cannot be trusted
  • Often difficult to identify trends