The Atmospheric System (DP IB Geography)

Revision Note

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

Pie chart showing composition of air: 78% nitrogen, 21% oxygen, 0.96% other gases (mostly argon), and 0.04% carbon dioxide.
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-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

Diagram of incoming short-wave solar radiation showing types of waves penetrating the atmosphere, including radio waves, microwaves, infrared, visible light, UV, X-rays, and gamma rays.
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

Diagram showing solar radiation distribution upon entering Earth's atmosphere: 3% scatter reflection, 19% by clouds, 9% by ground, 17% absorption by molecules and dust, 3% by clouds, and 49% by ground.
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

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

nighttime-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

Diagram explaining how the sun's rays enter Earth's atmosphere. Some thermal energy is absorbed by greenhouse gases, heating Earth, while some escapes into space.
Greenhouse gases absorb and then re-emit energy into the atmosphere

Examiner Tip

Don't get confused - the greenhouse effect is a natural process and is necessary for life on Earth. The accelerated or enhanced greenhouse effect refers to the changes in the greenhouse effect (mostly due to human activity) that are commonly referred to as global warming. 

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

Examiner Tip

Do not confuse the ozone layer with global warming. 

Yes ozone is a greenhouse gas, but the ozone layer protects the Earth from ultraviolet light.

Ozone is different because it absorbs incoming UV light and outgoing infrared light from the Earth.

The hole in the ozone layer increases the rate of skin cancer by allowing more UV rays to enter the atmosphere. It has no effect on incoming solar energy.

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