Changes in the atmosphere

Changes in
the atmosphere

Greenhouse effect

is a warming of the lower atmosphere and surface of a planet by a complex process involving sunlight, gases, and particles in the atmosphere. On the earth, the greenhouse effect began long before human beings existed. However, recent human activity may have added to the effect. The amounts of heat-trapping atmospheric gases, called greenhouse gases, have greatly increased since the mid-1800's, when modern industry became widespread. Since the late 1800's, the temperature of the earth's surface has also risen. The greenhouse effect is so named because the atmosphere acts much like the glass roof and walls of a greenhouse, trapping heat from the sun.

Causes of climate change
Impact Global Warming
Limited Global Warming
Agreement on global warming
Analyzing global warming
Kyoto Protocol
Greenhouse effect
Scientific research
Why climates vary
Ocean problems
Southern Ocean
Pacific Ocean
Ozone hole
Environmental problems by petroleum
Changes in the atmosphere
Increasing Temperatures
Can Earth Explode ?
NASA Study
El Nino
The Procedure Of Implementation Afforestation And Reforestation Project Under The Clean Development Mechanism (CDM) In Indonesia
Reducing emissions from deforestation and forest degradation (REDD) in developing countries



Human activity has caused small but important changes in the composition of the air. The amounts of many gases in the air, such as carbon dioxide, are increasing at significant rates. Carbon dioxide enters the atmosphere whenever coal, oil, or other fuels containing carbon are burned. Since the early to mid-1800's, the use of enormous amounts of these fuels has led to a 25 percent increase in the amount of carbon dioxide in the air. Levels of methane and nitrous oxide have more than doubled, and there were no chlorofluorocarbons (CFC's) in the atmosphere before 1930. CFC's are synthetic substances that were formerly used widely as refrigerants in air conditioners and refrigerators and as propellants in aerosol spray products.

Many scientists believe that the increases in the gases and the introduction of CFC's has strengthened the greenhouse effect. A strengthening of this effect would produce global warming, an increase in the average temperature of Earth's surface. (See GLOBAL WARMING.)

CFC's are also involved in the weakening of the protective layer of ozone in the stratosphere and troposphere. CFC's are harmless near the ground, but cause damage when they drift up into the stratosphere and troposphere. There, they break apart and release chlorine atoms. The chlorine reacts with the ozone, converting it into ordinary oxygen molecules. This conversion enables an increased amount of harmful ultraviolet radiation to reach Earth's surface. In 1990, the United States and most other industrialized countries agreed to stop production of most CFC's.

The study of air

Since ancient times, people have known that air is important to life. During the 400's B.C., Empedocles, a Greek philosopher, suggested that four elements-air, earth, fire, and water-combined in various proportions to make up all objects in the universe. Many other Greek scholars accepted this theory. In the 300's B.C., the Greek philosopher Aristotle wrote Meteorologica, which included his observations about the nature of air and the formation of weather.

The early philosophers and scientists could not test their theories about the air because they had no instruments to measure the air's properties. Around 1600, scientists began to use a type of thermometer to study air. Evangelista Torricelli, an Italian mathematician and physicist, invented the mercury barometer in 1643. In the mid-1600's, the Irish chemist Robert Boyle used the barometer to formulate the relationship between the volume of air and its pressure.

During the 1700's, scientists began to investigate the gases that make up the air. Oxygen was discovered by the Swedish chemist Carl Scheele in the early 1770's and independently by the English chemist Joseph Priestley in 1774.

In 1777, Antoine Lavoisier, a French chemist, realized that oxygen in the air enables objects to burn. Daniel Rutherford, a Scottish physician, discovered nitrogen in 1772. In 1894, the Scottish chemist Sir William Ramsay and the English physicist Baron Rayleigh together isolated argon. By the late 1800's, scientists had found that the composition of the air is the same all over Earth.

During the early 1900's, Norwegian researchers headed by the physicist Vilhelm Bjerknes discovered that the movement of enormous bodies of air, called air masses, helps determine weather conditions. The researchers showed that when a warm air mass and a cold air mass meet, a zone of rapidly changing weather, which they called a front, develops. Their model of weather systems vastly improved the accuracy of weather forecasting.

Since the mid-1900's, scientists have made much progress in developing equipment for studying the atmosphere. Today, weather balloons, radars, satellites, and lasers monitor atmospheric conditions, air pollution levels, and changes in the composition of the air. Meteorologists can analyze the data supplied by these devices to prepare detailed weather forecasts.

In December 1999, the National Aeronautics and Space Administration (NASA) launched Terra, the first satellite of an extensive program known as the Earth Observing System. Terra can monitor 16 factors that determine climate, including aerosols, air temperature, clouds, and water vapor.

Contributor: Stanley David Gedzelman, Ph.D., Professor of Meteorology, City College of New York.

Source : World Book 2005.