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
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
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
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
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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