Earth’s Energy System
By Reason McLucus
Those who talk about global warming take a very superficial view of
earth’s energy system. Even many who call themselves
scientists seem to think earth is a simple system of solar
radiation in, heating of earth's matter and radiation out. They
believe that earth must radiate as much energy out as it absorbs or it
will become hotter. They ignore the role of the biosphere and the
complex energy role of water. Earth would be uninhabitable if it
didn't convert much of the solar radiation it receives into other forms
of energy besides heat.
Much of the energy on earth exists as potential energy rather than just
the specific form of kinetic energy known as heat energy. The
standard definition of “heat energy” is the motion of
atoms/molecules. Gas molecules actually move around more as they
become “hotter”. Molecules that are part of a solid cannot move
independently so they vibrate along with the other molecules that
are part of the solid. Kinetic energy includes wind and objects
moving through the air or along the ground. This motion is not a
form of heat energy, but friction caused by moving through the air,
particularly for falling objects, may raise the temperature of the
object.
Earth’s climate cannot be understood without examining its
complex energy system.
Solar radiation provides most of the energy for earth. Radiation
hitting solid and liquid portions of earth is converted into heat
energy. Some radiation also heats the atmosphere directly.
Plants use solar radiation to store energy in the form of
chemical bonds of complex carbon molecules. This energy is a from of
potential energy. Cold blooded animals, and even some
warm blooded animals, use solar radiation for heat. Humans use
radiation to produce vitamin D and changes in skin pigment.
A significant amount of solar radiation is reflected back into space.
Geothermal energy provides some localized heating of earth.
Natural radioactivity provides a very limited amount of heat.
Human activity generates more heat than either source, but in areas of
human settlement which cover only a small portion of the earth. The
fossil fuels humans use for energy are essentially from solar radiation
that plants stored in the past. Geothermal energy could have a
significant affect in polar regions, such as the undersea volcano near
the recently collapsed Larson B ice shelf in Antarctica.
Humans can affect solar heating through alterations of
microclimates including alterations in the biosphere and
construction including roadways comprised of black asphalt.
Humans can reduce solar heating by encouraging plant growth including
planting trees. Replacing plant covered areas with roads and
buildings causes those areas to become hotter because radiation is
converted to heat rather than being stored in carbon molecules.
Elimination of trees by itself can lead to a process that causes areas
to become heat producing deserts. These deserts may in turn
affect the air circulation patterns that move heat energy around the
globe. There is less certainty about impact on ocean currents
that also circulate heat energy around the globe. The earth
receives sufficient energy from the sun to melt both polar ice caps,
but the heat is received and circulated unevenly. Thus melting of
ice caps could indicate an increase in heat circulation to polar areas
rather than an increase in the amount of heat energy on earth.
Water plays a major role in earth’s energy system. In solid form
as ice and snow it reflects most radiation striking it back into
space. Dirt or soot in the snow may convert radiation into heat
energy. Liquid water has a more complicated role. In the
liquid state, water is transparent to solar radiation but also reflects
some radiation into space depending on the angle at which the radiation
strikes it. Plants in water like plants on land store radiation
in carbon molecules. Fish are heated by solar radiation, or the
heat in the water. They use the heat energy for growth and to move
around. If the ocean fish populations decline, this heat
energy will not be converted to increasing the mass of the fish or
powering their movements. The oceans will warm as a result.
Traditional physics recognizes three basic forms of heat transfer:
conduction, radiation and convection. Physicists ignore a fourth
form of heat energy transfer, evaporation of water, because it does not
directly change temperature. Those who talk about global
warming concentrate on the radiation and ignore the fact that earth
isn’t a good radiator. Most of the earth is covered by water
which isn’t a good radiator because it is either reflective or
transparent to radiation. Substances which are transparent or
reflective are poor radiators.
Conduction plays a far more important role in atmospheric heating than
does radiation. As land, human structures and water warm up
they conduct heat to cooler air that is in what physicists call
“thermal contact”with the land, etc. The warmed air rises
allowing cooler air to replace it. The process of conduction
causes the substance receiving heat to become the same temperature as
the substance losing heat. The process depends primarily on the
difference in temperature of the two substances. The greater the
difference the more heat is transferred.
The amount of heat transferred by radiation on the other hand depends
only on the characteristics and temperature of the substance losing
heat. The substance emitting the radiation will only convert a
fraction of its energy into radiation which should mean that a
substance will transfer less heat energy by radiation than by
conduction. If those who talk about radiation heating of the
atmosphere have evidence that natural radiation can heat the
atmosphere they should provide that evidence instead of simply stating
the belief as if they had gotten it from the Bible or Koran.
The atmosphere does not trap heat by trapping radiation. The term
"greenhouse gases" is used because some falsely believe that
greenhouses remain warm by trapping radiation. Actually
greenhouses remain warm because they keep heated air from
escaping. Air doesn't transmit heat very well. Heat
energy passes through solid objects. Air molecules carry heat
around with them until they encounter cooler objects to transfer the
heat to or they rise and convert the heat to another form of kinetic
energy and potential energy.
Convection heat transfer involves the movement of heated air or water
to cooler areas and then conducting heat to the cooler substances
there. Examples of major convection heat transfer systems are the
North Atlantic Oscillation and the Gulf Stream. Low
pressure and high pressure systems are minor convection systems which
may redistribute hot or cold air.
Evaporation heat transfer differs from conduction and radiation in that
it only transfers heat energy into the air, but may not change the
temperature of the air. Evaporation reduces the temperature of
the substance the water evaporates from. Air temperature may also
drop if heat from the air contributes to the evaporation.
Water has some peculiar thermal properties. It has a high
specific heat of 1.0 (water needs 1 calorie per gram to raise the
temperature by 1 C). That is it takes more heat energy to
raise the temperature of water than to raise the temperature or air,
metals, etc. Air has a specific heat of about 0.2 depending upon
the degree of confinement. Water also has a high heat of
vaporization of 540 calories per gram at its boiling point. This means
that in order for water to evaporate each gram must absorb the amount
of heat necessary to heat 540 grams of water 1 C. This amount of
heat energy must be released for water vapor to condense back to a
liquid state. (Water at lower temperatures such as is found in
the ocean requires more energy to evaporate, but I will use the 540
calorie per gram figure to avoid complicating the discussion.)
When water evaporates from the ocean, lakes, etc. it carries this heat
energy into the atmosphere and may carry it up 10 miles or farther
before releasing it and condensing. Plants and animals also
transfer excess heat energy to the air by evaporating water.
Plants evaporate water through their leaves. Animals exhale water
vapor when they breathe. Some animals including humans cool
themselves by evaporating water from their skin. Soil also may transfer
heat to the air by evaporating water.
This process doesn’t directly raise the temperature of the air, but
does move heat energy up into the atmosphere. Increases in the water
vapor content of the air slows temperature changes because of water’s
high specific heat. The condensation of water in the air does
raise air temperature. With water’s high heat of
vaporization and specific heat, each gram of water vapor that condenses
in the atmosphere releases sufficient heat energy to heat over 2 kg of
air by 1 C. Water’s high heat of fusion of 80 calories per gram
increases the heating when water droplets freeze in the air. Water must
release 80 calories per gram of heat energy to freeze. This
freezing typically occurs during winter months or at higher altitudes
during summer.
The energy water vapor carries into the atmosphere provides the energy
involved in the production of lightning, especially the lightning that
occurs above clouds referred to by names such as “sprites” and “blue
jets”.
As water vapor rises in the atmosphere a portion of its heat energy
changes to a different form of kinetic energy to allow it to
rise. This kinetic energy then changes to potential energy.
When water falls as rain some of this potential energy turns to
kinetic energy and may move dirt or water around. Water that
becomes hail may carry enough energy to damage objects on the
ground. Water falling in higher altitudes retains some of its
potential energy when it hits the ground. If that water
subsequently flows through hydroelectric dams, the generators convert
some of that potential energy into electrical energy.
Atmospheric water that forms clouds can affect both air and ground
temperature. Clouds block the rise of warm air keeping heated air
closer to the ground. High air pressure also keeps heated air close to
the ground. A common misconception is that clouds cause
heating by blocking radiation, but any radiation would still move out
from under the cloud cover in microseconds.
On the other hand clouds reflect solar radiation back into space
preventing it from heating the earth’s surface. Clouds,
particularly the particles in clouds that water droplets condense on,
absorb some radiation and may produce sufficient heat to evaporate the
water in the clouds. This process is sometimes referred to as the sun
“burning off” the cloud cover. Radiation that evaporates
water in clouds does not heat the atmosphere itself.
Snow and ice are part of an important feedback loop that may affect
temperatures and climate. Snow reflects sunlight back into space
reducing the amount of heating. Thus as snow cover increases
temperatures will remain below freezing longer. Below freezing
temperatures mean precipitation that falls will wall as snow or ice
rather than rain. Lower temperatures are more likely to be close
enough to the dew point to encourage more snowfall. The amount of
water the air can hold increases with higher temperatures. The
dew point is the lowest temperature the air can fall to without having
to give up water.
When snow cover declines more land is open to sunlight and is heated by
the sun resulting in higher air temperatures. The higher air
temperatures mean the temperature will be more likely to remain above
freezing and precipitation will fall as rain instead of snow.
Those who blame humans for “global warming” ignore the possibly
significant impact human intervention in this feedback loop may be
having on climate. For example, in North America prior to
significant human settlement, vast areas would be covered with snow
with no open ground to allow solar heating of the air. Urban heat
islands allow snow to evaporate faster in the cities with some of the
heat gradually spreading to the countryside.
Clearing snow off rural highways may not seem like a significant act,
but the cleared roads provide the opportunity for solar heating of the
ground and air. As snow heats the pavement some of the heat
spreads to the surrounding ground allowing additional
melting. Pavement can become hot enough from solar
radiation that snow will not only melt, but some of it may even absorb
enough heat to evaporate.
This human affect on the snow feedback loop won’t eliminate winter, but
may reduce its length and allow more days with above freezing
temperatures during winter. Early snows will be less likely to
trigger early cold weather. Early snows that remain on the ground
will slow warm ups after early movement of cold Arctic air into
temperate areas.
Those who talk about “global warming” oversimplify earth’s energy
system. Earth is not a simple system involving radiation in and
radiation out. Solar radiation received by earth is converted
into other forms of energy and used for such activities as powering the
biosphere.
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