The Concept of Energy 87
forms in order to be transferred to us. It began as nuclear energy and then
through successive processes became heat energy, light energy, chemical
energy and finally the heat energy and kinetic energy of our bodies.
Global Warming and Greenhouse Gases
The sunlight from Sun warms the Earth constantly heating the
atmosphere and the surface of the Earth. As the atmosphere and the
surface of the Earth heat up a certain amount of that heat is radiated back
into outer space otherwise our planet would overheat to the point that life
on our planet would not be sustainable. There has been a delicate balance
in nature in which the amount of incoming energy and outgoing energy
are approximately equal which keeps the temperature on Earth in the
moderate range. Over the course of time there have been moderate
fluctuations in the amount of energy coming from the Sun, due to
volcanic activity, fluctuations in the Sun’s output and fluctuations in the
Earth’s orbit about the Sun known as Milankovich cycles. These
fluctuations have resulted in Ice Ages, the last one of which ended
10,000 years ago. Another factor affecting the warming and cooling of
the planet is fluctuations in albedo, the reflection of sunlight back into
outer space due to ice and snow cover. One of the factors affecting the
amount of heat radiated out from the Earth into outer space is the amount
of carbon dioxide, CO 2 , in the atmosphere, which is approximately
0.0383% of all the gases in the atmosphere. CO 2 , however, absorbs a
significant percentage of the heat radiated off the surface of the Earth and
therefore contributes to the warming of the planet.
The balance of CO 2 in the atmosphere before the massive intervention
of industrial age human activity was maintained by plants absorbing or
breathing in CO 2 and exhaling oxygen. The replenishing of CO 2 into the
atmosphere comes form the respiration of animals breathing in oxygen
and exhaling CO 2. There is also a certain amount of CO 2 that enters the
atmosphere due to forest and brush fires caused by lightning and certain
amounts of emissions due to volcanic activity. That balance has been
seriously eroded by our burning of fossil fuels, which is dumping large
quantities of CO 2 into the atmosphere. As the amount of CO 2 has
increased a greenhouse effect has taken place where more energy in the
form of sunlight has entered the Earth’s atmosphere than is now exiting.
There is an analogy with a glass greenhouse because glass is transparent
to visible light but is opaque or blocks the lower frequency infrared