From Thermodynamics to Economics and Ecology - Thanatia: The Destiny of the Earth's Mineral Resources - page 66

energy (high quality energy), will eventually degrade into heat at the lowest possible
temperature. All other types of energy will arrive at this point sooner or later.
This is why the Second Law is so devastating, since it truly announces dissipa-
tion. Thermodynamics does not state when this will happen but does guarantee
that it will happen. It is an empirical fact. Expressing this principle in a mathe-
matical way is very simple. If an amount of heat, Q flows spontaneously from hot
bodies (T) to cold ones (T 0 ), with T > T 0 , then
Q
T 0

Q
T

i (3.3)

f i

Having understood this, it becomes easier to link degradation to entropy. The
cold body has gained more entropy than the hot body has lost. The difference
becomes greater as the temperature range between the two increases. This phe-
nomenon is referred to as generated entropy () and increases with the degradation
of energy quality. Since all bodies tend to irreversibly dissipate their energy in form
of heat until reaching the temperature of their surroundings, entropy will always
be generated. Only in the best possible case, known as the reversible process, is
entropy generation zero. In any process undertaken by a system, its entropy and
that of the surrounding environment will increase or, in the best case scenario will
remain constant. In a mathematical way the Second Law can be expressed as:

S universe > 0; with S universe = S system + S surroundings (3.4)

With the above explanations, it is easier to understand what ecological
economists refer to when they use the terms “high entropy” or “low entropy” to
describe the world around them. Low entropy examples include natural feedstock,
fossil fuels, food, wood, a lake or even the sun. A fossil fuel spontaneously reacts
with oxygen in the air and its energy is transformed into heat. Food is metabolised
in a controlled combustion reaction, maintaining body temperature constant and
providing energy to meet its needs. Later that same energy dissipates and heats the
environment. Thermal energy is an unimaginably huge energy drain. This simple
fact allows for a better understanding of Nature.
These ideas bring another reflection: entropy production or destruction does
not always hold negative consequences as seen in the beauty of a river's waterfalls.
Nature does not attempt to restrict the Second Law machine. On the contrary,
Man by installing a hydraulic turbine avoids entropy generation but at the cost of
the river's aesthetics.
It is worth noting that the greatest entropy production taking place on Earth is
not due to anthropogenic activity but rather it is solar in origin. The sun radiates
heat towards the Earth, which is at an average temperature of around 288 K, at
approximately 5,700 K (i.e., the sun's energy is 95% pure exergy). In turn, the
Earth sends this energy back to space at about 2 K, meaning that the Earth's
net energy balance is almost zero. Waves, winds, the formation of clouds, and
the heating of the Earth are only intermediate manifestations of that dissipation.