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Infrared, Gases and the Greenhouse Effect

by Ron Kurtus (2 February 2007)

The Earth is heated by absorption of light from the Sun. The heating process results in infrared radiation being emitted from the Earth. The Greenhouse Effect is the process where certain gases in the atmosphere absorb this infrared radiation and heat the Earth further. This effect is important in keeping the Earth at a reasonable temperature, but an excess of absorbing gases in the atmosphere can drastically change the climate and cause numerous problems.

Questions you may have include:

• How is the Earth heated by radiation?
• What is the Greenhouse Effect?
• What problems can be caused by excessive heating of the atmosphere?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Useful tools: Metric-English Conversion | Scientific Calculator.

How the Earth is heated

The Earth is heated to relatively moderate temperatures by the absorption of some of the Sun's radiated energy. About 30% of the light from the Sun is reflected, while the other 70% is absorbed, resulting in heating the Earth.

Although the radiation that we see from the Sun is visible light, the range of wavelengths of radiation extends far beyond the visible to include infrared and ultraviolet radiation.

Atmosphere absorbs radiation

Ozone (O₃) in the atmosphere absorbs much of the harmful ultraviolet rays from the sun. Oxygen (O₂), water vapor (H₂O) and carbon dioxide (CO₂) in the atmosphere absorb some of the infrared radiation. This absorption of the ultraviolet and infrared radiation by these molecules provided them with more energy, resulting in heating the atmosphere.

Some reflected and the rest absorbed

Some of the visible and infrared radiation that passes through the atmosphere is reflected back into space by the bodies of water—oceans and lakes—and snow cover.

The remaining radiation is absorbed in the ground and water around the Earth. This material becomes warm and re-radiates longer wavelength infrared, which is then absorbed in the atmosphere.

This absorption of re-radiated infrared by gases in the atmosphere—especially carbon dioxide—heats up the atmosphere even more and is called the "Greenhouse Effect" by many people.

(See Infrared Radiation for more information about that subject.)

Greenhouse Effect

The Greenhouse Effect is really a misnomer and not a correct description of how the Earth is heated by the Sun. A greenhouse uses glass windows to trap the infrared in the building, thus heating its air. In the Greenhouse Effect, gases in the Earth's atmosphere absorb the radiation and thus heat the air. It is a much stronger effect than simply having glass windows trap infrared and warm air.

Although this "Greenhouse Effect" has done a good job at keeping the temperatures on the Earth at a reasonable level over many years, the excess of certain gases in the atmosphere has thrown that level off kilter and has resulted in what is called global warming.

Excess of carbon dioxide

Carbon dioxide seems to be the most active molecule in absorbing infrared radiation and thus in heating the atmosphere. CO₂ has stayed at the proper percentage in the atmosphere until recently, when an increasing amount of the gas has been emitted due to the burning of fossil fuels. Automobile exhaust and industrial smoke contribute the most CO₂.

Problem of methane

A potential problem is that the recent increase in temperature is melting the tundra in the Siberian area of Russia. This is causing the release of enormous quantities of methane gas (CH₄) that has been locked in the frozen soil. This gas can cause a greater absorption of infrared radiation than CO₂, thus causing an even greater heating of the atmosphere. Once the tundra starts to melt, even getting rid of automobiles will not stop the global warming trend.

Warming trend seen

Although the average temperature around the Earth has fluctuated over the eons, it seems that there has been a rapid increase in recent years as the world becomes more industrialized. This has been noticed in the melting of glaciers that have existed for thousands of years.

Note that there are some who claim that global warming is not a problem and is not caused by the greenhouse effect. But most scientists say that the gases are caused by human activity.

Problems caused by global warming

Runaway increases in the temperature of the Earth can cause numerous problems. The Arctic and Antarctic ice caps can start to melt, thus raising the level of the ocean and flooding many coastal cities.

Increased temperature will reduce the amount of snowfall in the mountains. Many countries depend on the runoff of that snow to help irrigate their farms and provide food for their people.

Increased temperatures mean more energy in the air, and thus more violent storms.

Existing plants and crops depend on certain climate conditions to grow. Increased average temperatures can disrupt the growing process in many areas.

Summary

The Greenhouse Effect is the process where infrared radiation from the Sun is absorbed by gases in the atmosphere, thus helping to heat the Earth. An excess of absorbing gases such as carbon dioxide in the atmosphere can drastically change the climate and cause numerous problems.

Answers to Readers' Questions

This is the only Earth we have

Resources

The following resources provide information on this subject:

Websites

Physical Science Resources

Books

Top-rated books on Global Warming

Top-rated books on Physical Science

Miscellaneous

Mini-quiz to check your understanding

1. What does carbon dioxide in the atmosphere do?

2. What can happen when there is an excess of CO₂ and CH₄ in the atmosphere?

3. Why are there more violent storms with increased temperatures?

If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.

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Infrared, Gases and the Greenhouse Effect