The Greenhouse EffectThe greenhouse effect is an increase in the atmospheric temperature causedby increasing amounts of greenhouse gases. These gases act as a heat blanketinsulating the Earth’s surface absorbing and trapping heat radiation which normallyescapes 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 coolingis the first process. This process uses the clouds which cover 60% of the earth’ssurface to reflect 30% of the solar radiation. It also uses a sulfate haze, whichis formed by sulfur dioxide from industrial sources that enter the atmosphere andreact with compounds to form a high-level aerosol. These cool the atmosphere byblocking us from direct contact with the sun.
The reflection of the sunlight isreferred to as planetary albedo and contributes to the overall cooling. The second is the warming process. This is when light energy comes throughthe atmosphere and is absorbed by Earth and transformed to heat energy at theplanet’s surface. The infrared heat energy then radiates upward into space. Therethe greenhouse gases found naturally in the troposphere absorb some of the infraredradiation. The gases insulate the Earth, but do eventually allow the heat toescape.
Without these greenhouse gases the earth would be would 33 C colder. Global temperature is a balance of the effects of the factors leading toglobal cooling, and warming. Unfortunately, increased emissions of greenhousegases increase the warming process. For example, every kilogram of fossil fuelsburned equals 3 kilograms of carbon dioxide ( the mass triples because each carbonatom 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 tonsof C02 to the atmosphere. This has increase the carbon dioxide concentrationsby 25% and has cause temperatures to increase more than 0. 7 C over the last hundredyears. We hope that the forests will act as a sink for carbon dioxide but insteadthey are a net source.
This is because the forests are being cut and burned adding1 to 2 billion tons annually to the 6 billion tons of carbon already from industrialprocesses. Fortunately, the top 300 meters of oceans absorb most of the carbondioxide emitted by burning fossil fuels. Other factors are known to increase the greenhouse effect. These factorare water vapor, methane, nitrous oxide, CFC’s and other halocarbons. Watervapor is also a major factor in what has been called the supergreenhouse effectin the tropical Pacific ocean.
Water vapor traps energy that has been radiatedback to the atmosphere. The high concentration of H2O vapor contributessignificantly to the heating of the ocean surface and lower atmosphere in thetropical Pacific. Methane (CH4) is a product of microbial fermentative reactions and is alsoemitted from coal mines, gas pipelines, and oil wells. Methane is graduallydestroyed, 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 othersbecause of its long residence time of 170 years. CFC’s and other halocarbons are found in refrigerants, solvents, and fireretardants. Halocarbons have a greater capacity, 10 000 times, for absorbinginfrared radiation, which is about 60% more, than CO2.
Although there is increasein the application of some of these gases, they will decrease in importance inthe future leaving carbon dioxide as the primary dilemma. In 1981, James Hansen of NASA invented a model with an ability to trackknown temperature changes and link them to past and future carbon dioxide levelsas well as global temperature changes. The model suggested the combination ofCO2 and volcanic emissions was responsible for most of the observed changes intemperature during the 1980’s. A trend of warming of more than 0. 7 C coincideswith an increase of 25% in carbon dioxide. Two major impacts of greenhouse effect are regional climatic changes anda rise in sea levels.
A climactic change will lead to variations in temperature. Scientists expect more precipitation which may prove to be disastrous for NorthAmerica by flooding rivers and lakes. A rise in the sea levels is anticipated because of an increase in thermalexpansion 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 burycontinents.
In order to control the effects of global warming we must first admit thatit’s occurring, then take steps to end it. We must stop burning the trees andnot replacing them. Most importantly, we must stop polluting the air.Science Essays
