The Atmospheric System (SL IB Geography)

• The atmosphere is an envelope of mixed, gases
• Which is held in place by gravitational attraction
• It consists of nitrogen (78%), oxygen (21%) and 1% trace gases 

Gasses of the atmosphere

Other gases include water vapour, nitrous oxide, ozone, and methane 

Atmospheric layers

• The atmosphere is 10,000 km in height
• But gravity compresses 99% of the atmosphere to within 40 km of the Earth's surface 
  • 50% of the atmosphere is in the first 5.6 km

Atmospheric layers

Atmospheric heat budget

• The Sun is Earth’s primary source of energy
• It provides more energy in an hour than humans use in a year 
• Energy is received as short-wave radiation - insolation

Insolation

The atmosphere can block harmful waves from reaching the Earth’s surface

 

• Earth's atmospheric heat budget depends on the balance between:
  • Insolation and
  • Outgoing long-wave radiation 
• Some energy is lost passing through the atmosphere, but there is an overall net gain of energy at the surface 
• Polar regions have a net deficit (they receive about 24% of insolation) due to absorption, reflection and scattering – albedo effect 
• The atmosphere itself has an overall net deficit of energy 
• To compensate, heat is moved from the surface to the atmosphere by radiation, conduction and release of latent heat – the natural greenhouse effect

Earth’s energy budget

The global energy budget model assumes that the surface is flat grassland, hence differences between polar and equatorial regions

 

Atmospheric energy budget as a system

• An energy budget refers to:
• The amount of energy entering a system
• The amount leaving the system
• The transfer of energy within the system

 

Atmospheric Energy System

Input	Energy from the Sun and Earth
Output	Loss of energy to space
Transfer/flow	Convection, conduction and radiation
Stores	Land, oceans, clouds and atmosphere

• If the atmosphere loses more energy than it gains, it will cool down
• However, if the atmosphere gains more energy than it loses, it will heat up
• This is global warming, where more energy is retained in the atmosphere
• There is also the difference between day and night or the diurnal energy budget

Daytime energy budget

• There are 6 components to the daytime energy budget:
  • Incoming (shortwave) solar radiation (insolation) 
    • Strongly influenced by cloud cover and latitude
    • At the equator, the Sun’s rays are more concentrated than at the poles
  • Reflected solar radiation 
    • The amount of reflection depends on the type of surface
    • Referred to as the albedo effect, the higher the percentage, the more insolation is reflected
  • Surface absorption 
    • Depending on the surface, heat is transferred either quickly or slowly to the sub-soil layers
  • Sensible heat transfer (conduction and convection)
    • This involves losing or gaining energy without a phase change
      • Water vapour doesn't change, but moves heat from one area to another
  • Long-wave radiation
    • This is emitted by the surface and passes into the atmosphere, and eventually into space
  • Latent heat transfer (evaporation and condensation)
    • This does involve a phase change - gas to liquid, etc. and uses a lot of energy
    • Sublimation is when a solid turns to gas without becoming a liquid and vice versa

Daytime energy budget

Sensible and latent heat transfers

• Sensible heat is felt when touching a warm object
• Can be measured with a thermometer
• Moves heat from warmer to colder objects by:
  • Conduction: direct contact
  • Convection: fluid moves heat away from a surface (such as the ocean)
• Latent heat (hidden heat) is energy that is absorbed, stored and released at a molecular level
• It cannot be measured by a thermometer
  • For example, when liquid changes to vapour or solid to liquid, heat energy is absorbed from the surroundings
  • When the vapour turns back to liquid or solid, latent heat is released, warming the surroundings 
  • This is why it is cooler by water in summer (water has taken the heat from its surroundings) and warmer in winter (water is releasing heat to its surroundings)

Night-time energy budget

• There are 4 components to the night-time energy budget:
• Long-wave radiation 
• Sub-surface radiation 
• Sensible heat transfer (conduction and convection)
• Latent heat transfer (condensation)

Night-time energy budget

There is no insolation at night, therefore, energy is released 

 

• Long-wave radiation 
• During the night, there is a net loss of energy from the surface
• With clear skies, temperatures fall quickly
• Under cloudy conditions, the loss is reduced as clouds return some longwave radiation to the surface
• Sub-surface supply 
• The heat stored during the day is transferred (conducted) to the cool surface during the night
• This energy supply can reduce the size of night-time temperature drop on the surface
• Sensible heat transfer (conduction and convection)
• Moving warm air adds energy and helps keep temperatures up
• But, if cold air moves in, energy levels will fall, possibly reducing temperatures
• Latent heat transfer (evaporation and condensation)
• At night, water vapour near the ground can condense to form dew
• The process releases latent heat, and supplies energy to the surface, producing a small gain of energy
• However, if there is enough evaporation, this can lead to cooling

• Water vapour, CO₂, methane, ozone, NOx and CFCs all contribute to keeping Earth  warm
• They are natural greenhouse gases (GHGs) and keep a global average temperature of 15°C
• Without them, the Earth’s global temperature would be around -18°C and not suitable for life 

Natural greenhouse effect

Greenhouse gases absorb and then re-emit energy into the atmosphere

Levels of GHGs

• • Water vapour is the most abundant greenhouse gas 
    • It accounts for about 95% of GHGs by volume
    • Water vapour is responsible for 50% of the natural greenhouse effect
    • Human activities indirectly affect temperature and moisture through:
      • Deforestation, land-use changes, and burning fossil fuels
  • Carbon dioxide (CO₂) accounts for 20% of the greenhouse effect
    • Levels have risen from 315 parts per million (ppm) in 1950 to over 421 ppm in 2022
    • 2050 levels are expected to be 550 ppm 
    • Increase is due to human activities - burning fossil fuels and deforestation
      • Deforestation also decreases carbon storage, as trees remove CO2 from the atmosphere during photosynthesis

• • Methane accounts for 17% of the natural greenhouse effect 
    • Methane is 28 times more potent than CO₂ at warming the Earth
    • Produced naturally and through human activities such as:
      • The decay of organic matter in wetlands, forests, and oceans
      • Agriculture (particularly rice growing and livestock farming), fossil fuel extraction, and waste landfills

• • Chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs) account for 1.5% of GHGs in the atmosphere
    • These are man-made chemicals that are:
      • 10,000 times better than CO₂ at trapping heat
      • Increasing at a rate of 6% per year
      • Banned by many countries as they deplete the ozone layer - 1 CFC atom can destroy thousands of ozone molecules

• • • HFCs are weak ozone-depleting substances but are strong greenhouse gases