The Atmospheric System (DP IB Geography)

Structure of the Atmosphere

• 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

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

Energy Balance

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

• 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

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

• 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

Natural Greenhouse Effect

• 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

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