temperature increases. If an object loses more energy than it gains, its temperature
decreases. If an object remains at a constant temperature, incoming and outgoing
energy are approximately equivalent.
Heat can be transferred in three different ways. The first is via conduction. This
is a molecule-to-molecule flux of energy and is most efficient in the closely packed
molecules of solids and least efficient in the atmosphere. Thus, conduction is
important in heating and cooling of the soil while negligible in the atmosphere
above shoe top height.
The second mode is via convection. In convection, heat is transferred from
place to place along with the flow of a substance. In our environment both the
atmosphere and water are capable of convective transfer of energy. Convection is
important in bringing energy from Earth’s surface up through the troposphere
and convection sluggishly causes vertical motion in the denser fluid of the oceans.
The third mechanism of heat exchange is via electromagnetic radiation. All
objects above absolute zero (− 273 °C) radiate electromagnetic energy and our Earth
environment is far above absolute zero. The hotter an object, the greater its heat con-
tent by volume and the greater its total electromagnetic emissions. The wavelengths
of the emissions are controlled by the temperatures. Hot objects radiate at relatively
short wavelengths and cool objects radiate at relatively long wavelengths. For in-
stance, the sun’s energy has its most plentiful wavelengths in the visible portion of
the spectrum while the lesser energy in the Earth system is radiated most plentifully
at wavelengths 20 times as long. Electromagnetic radiation does not need any
medium through which to propagate. It can be transmitted through the void of space
and through media such as water or atmosphere in which the molecules are not
closely packed. It occurs at “the speed oflight,” which is immensely faster than
either conduction or convection.
Somewhat more complicated than conduction and convection is the disposition
of electromagnetic energy. As electromagnetic energy contacts mass at Earth’s
surface or in its atmosphere, one of three things can happen: (1) The energy can
be transmitted through the mass and not add to its heat content (such as we are able
to view sunlight that has passed through the entire atmosphere, (2) the energy can
be absorbed by the mass and thus increase the heat content of the mass, or (3) the
energy can bounce off the mass in one direction (reflection) or multiple directions
(scattering) and not add to the heat content of the mass. It is the absorption of
energy by mass that increases its heat and accordant temperature. Different types
of objects heat differently because their physical nature makes them transmit,
absorb, and reflect (and refract) electromagnetic energy differentially. For in-
stance, snow does not melt as quickly as one might suppose because the large
majority of solar radiation is reflectedwithout having a chance to increase the
snow’s heat content.172 Heating and Cooling