Fundamentals of the physical environment,
Chapter 2, 3, 4, 5, 6, 8
2. Energy and earth
CONCEPTS OF ENERGY
Radiant, thermal, kinetic, chemical and potential energy are the forms of energy that are important for
environmental processes.
Radiant energy: The form of energy the sun emits > short wave radiation.
Thermal (heat) energy: Most of the energy that gets absorbed converts into thermal energy. It warms the
surface and atmosphere of the earth by exciting the molecules of which they are composed.
Kinetic energy: Kinetic energy is the energy of movement. Every moving object has kinetic energy.
Chemical energy: Chemical energy is the energy bound up in a chemical structure. It gets released when the
substance breaks down.
Potential energy: Potential energy is related to gravity. The higher an object the more potential energy it has
because it can fall a greater distance.
Sensible and latent heat
There are two other forms of thermal heat: Sensible heat and latent heat.
Sensible heat is the exchange of warm air down a temperature gradient. Latent heat is the energy that is
‘trapped’ in different forms of water. This energy gets released when for example water vapour condensates.
Methods of energy transfer
The energy the earth receives is not equally distributed. As a result of these differences, spatial transfers of
energy take place, for energy is redistributed to minimize the inequalities. There are three forms of energy
transfer for thermal heat: Radiation, convection and conduction.
Radiation: Radiation is the process by which energy is transmitted through space (mostly because of
electromagnetic waves).
Convection: Convection is the physical movement of objects containing heat. The object is not a solid form, for
example air or water. Convection can transfer both sensible and latent heat.
Conduction: Conduction is the movement of heat from molecule to molecule. This happens when a molecule
which contains much heat collides with a molecule that doesn’t contain much heat. A part of the heat will then
get passed on to the other molecule.
Energy transformations
The nature of energy often changes, but the amount of energy always stays the same. Energy can always be
converted to other forms of energy, but they follow defined pathways.
,GENERAL PATTERNS AND PRINCIPLES OF ELECTROMAGNETIC RADIATION
Every object that has a temperature above absolute zero (0K or -237 degrees Celsius) emits radiation.
If temperature rises, the intensity of the radiant energy increases and the wavelength decreases.
If temperature fall, the intensity of the radiant energy decreases and the wavelength increases.
In addition, the amount of radiation reaching any object is inversely proportional to the square of the distance
from the source.
Radiation can penetrate matter (e.g. x-rays), but most of the time it gets reflected or absorbed.
How much energy can be absorbed depends on multiple factors: the physical structure of the material, the
colour, the surface roughness, the angle of the incoming radiation and the wavelength.
A black body can absorb all radiation. A perfect black body does not exist. An object absorbs energy and
reflects the remainder. The amount of radiation reflected from a surface is called the albedo. Formula albedo:
The amount of energy reflected/total amount of energy = a percentage.
Solid substances absorb most energy, but gasses are very selective. This means that the atmosphere, which
partly exists of gasses, can only absorb and emit certain wavelengths. The atmosphere is also composed of
dust, water droplets and ice crystals. These particles reflect light waves in different directions. This process is
called scattering and it only changes the direction of the wavelengths. Gas molecules are most effective at
scattering light in the blue wavelength, which makes the atmosphere look blue. When the sun sets or rises the
angle of the wavelength is different which makes the sky look red or more colourful.
Absorption of radiant energy has more far-reaching consequences than reflection or scattering. If an object
absorbs radiant energy its temperature will rise because the radiant energy transforms into thermal energy.
Re-radiation will have a different temperature and will therefore be
emitted at a different wavelength.
THE PLANETARY SETTING
The energy input for system earth is radiant energy from the sun. The
output is reflected and reradiated energy. The earth could be modeled as
a black box system if the model only shows the amount of input and
output.
Exogenetic energy
The input of energy for system earth is called exogenetic because it
originates outside of the earth. The input of energy to earth is an average
values because it varies a lot. There are multiple reasons for these variations: The rotation of earth around its x-
, axis every 24 hours, the rotation of earth around the sun every 365 days and the angle of earths x-axis which
can also change but in a timescale of thousands years.
The sun also emits energy that is called corpuscular radiation or solar wind which is composed of ionized
particles and magnetic fields. There is a connection between variations in the strength of the solar wind and
activity on the surface of the sun. The solar wind interacts with the magnetosphere, the magnetic field that
surrounds Earth, and this interaction is visible as the aurora.
Diurnal variation
Earth rotates on its x-axis which leads to a changing
distribution of incoming solar radiation, insolation. The size
of the area the sunlight reaches and the intensity both
depend on the angle of the insolation, as seen in the next
figure. The duration of the day also affects the amount of
radiation received.
Seasonal variation
Seasonal variations arise from the changing axial tilt of Earth
relative to the sun throughout the year. The orbit of the sun
is not a circle but an ellipse, which is the reason why in
January the earth is closer to the sun than in June. This also
means the amount of energy received varies.
Endogenetic energy
A small proportion from the energy received comes from the earth itself, and thus it is called endogenetic
energy. The most obvious source is the earths hot interior.
This form of energy only accounts for 0.0001% of the total energy supply.
ENERGY OUTPUTS OF THE GLOBE
Nature of earth’s energy output
The output of energy is in radiant form, but not identical to the input. Earth has modified it by different
processes.
- Some of the incoming energy gets reflected to space by clouds or the surface with little change in
radiative properties.
- Some of the insolation gets scattered. Most of it towards earth, but some of it back to space as short-
wave energy.
