The Greenhouse Effect
The greenhouse effect is an increase in the atmospheric temperature caused
by increasing amounts of greenhouse gases. These gases act as a heat blanket
insulating the Earth’s surface absorbing and trapping heat radiation which normally
escapes from the earth. They include carbon dioxide, water vapor, methane,
nitrous oxide, CFC’s, and other halocarbons.
The earth’s atmosphere goes through two processes constantly. Global cooling
is the first process. This process uses the clouds which cover 60% of the earth’s
surface to reflect 30% of the solar radiation. It also uses a sulfate haze, which
is formed by sulfur dioxide from industrial sources that enter the atmosphere and
react with compounds to form a high-level aerosol. These cool the atmosphere by
blocking us from direct contact with the sun. The reflection of the sunlight is
referred to as planetary albedo and contributes to the overall cooling.
The second is the warming process. This is when light energy comes through
the atmosphere and is absorbed by Earth and transformed to heat energy at the
planet’s surface. The infrared heat energy then radiates upward into space. There
the greenhouse gases found naturally in the troposphere absorb some of the infrared
radiation. The gases insulate the Earth, but do eventually allow the heat to
escape. Without these greenhouse gases the earth would be would 33 C colder.
Global temperature is a balance of the effects of the factors leading to
global cooling, and warming. Unfortunately, increased emissions of greenhouse
gases increase the warming process. For example, every kilogram of fossil fuels
burned equals 3 kilograms of carbon dioxide ( the mass triples because each carbon
atom in fuel bond to two oxygen atoms, in the course of burning, and forms C02. )
6 billion tons of fossil fuel carbon are burned each year adding 18 billion tons
of C02 to the atmosphere. This has increase the carbon dioxide concentrations
by 25% and has cause temperatures to increase more than 0.7 C over the last hundred
We hope that the forests will act as a sink for carbon dioxide but instead
they are a net source. This is because the forests are being cut and burned adding
1 to 2 billion tons annually to the 6 billion tons of carbon already from industrial
processes. Fortunately, the top 300 meters of oceans absorb most of the carbon
dioxide emitted by burning fossil fuels.
Other factors are known to increase the greenhouse effect. These factor
are water vapor, methane, nitrous oxide, CFC’s and other halocarbons. Water
vapor is also a major factor in what has been called the supergreenhouse effect
in the tropical Pacific ocean. Water vapor traps energy that has been radiated
back to the atmosphere. The high concentration of H2O vapor contributes
significantly to the heating of the ocean surface and lower atmosphere in the
Methane (CH4) is a product of microbial fermentative reactions and is also
emitted from coal mines, gas pipelines, and oil wells. Methane is gradually
destroyed, but it is added to the atmosphere faster than it can be broken down.
Nitrous oxide (N2O) can be found in biomass burning, chemical fertilizers,
and fossil fuel burning. Nitrous oxide is more dangerous than some of the others
because of its long residence time of 170 years.
CFC’s and other halocarbons are found in refrigerants, solvents, and fire
retardants. Halocarbons have a greater capacity, 10 000 times, for absorbing
infrared radiation, which is about 60% more, than CO2. Although there is increase
in the application of some of these gases, they will decrease in importance in
the future leaving carbon dioxide as the primary dilemma.
In 1981, James Hansen of NASA invented a model with an ability to track
known temperature changes and link them to past and future carbon dioxide levels
as well as global temperature changes. The model suggested the combination of
CO2 and volcanic emissions was responsible for most of the observed changes in
temperature during the 1980’s. A trend of warming of more than 0.7 C coincides
with an increase of 25% in carbon dioxide.
Two major impacts of greenhouse effect are regional climatic changes and
a rise in sea levels. A climactic change will lead to variations in temperature.
Scientists expect more precipitation which may prove to be disastrous for North
America by flooding rivers and lakes.
A rise in the sea levels is anticipated because of an increase in thermal
expansion and the melting of ice caps and ice fields. Like extensive rainfalls,
a rise in the ocean will flood lakes and rivers covering land and may someday bury
In order to control the effects of global warming we must first admit that
it’s occurring, then take steps to end it. We must stop burning the trees and
not replacing them. Most importantly, we must stop polluting the air.