10.16: Greenhouse Effect

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How does the atmosphere resemble a greenhouse?

Farmers use greenhouses to extend the growing season. A greenhouse traps thermal energy. Days that are too cool for a growing plant can be made to be just right. Similar to a greenhouse, greenhouse gases in the atmosphere keep Earth warm.

The Greenhouse Effect

When sunlight heats Earth’s surface, some of the heat radiates back into the atmosphere. Some of this heat is absorbed by gases in the atmosphere. This is the greenhouse effect, and it helps to keep Earth warm. The greenhouse effect allows Earth to have temperatures that can support life.

Gases that absorb heat in the atmosphere are called greenhouse gases. They include carbon dioxide and water vapor. Human actions have increased the levels of greenhouse gases in the atmosphere (Figure below). The added gases have caused a greater greenhouse effect. How do you think this affects Earth’s temperature?

Diagram of the natural and human enhanced greenhouse effect

Human actions have increased the natural greenhouse effect.

Like a blanket on a sleeping person, greenhouse gases act as insulation for the planet. The warming of the atmosphere is because of insulation by greenhouse gases. Greenhouse gases are the component of the atmosphere that moderate Earth’s temperatures.

Greenhouse Gases

Greenhouse gases include CO₂, H₂O, methane, O₃, nitrous oxides (NO and NO₂), and chlorofluorocarbons (CFCs). All are a normal part of the atmosphere except CFCs. The table below shows how each greenhouse gas naturally enters the atmosphere (Table below).

Greenhouse Gas	Source
Carbon dioxide	Respiration, volcanic eruptions, decomposition of plant material; burning of fossil fuels (driven by humans)
Methane	Decomposition of plant material under some conditions, biochemical reactions in stomachs
Nitrous oxide	Produced by bacteria
Ozone	Atmospheric processes
Chlorofluorocarbons	Not naturally occurring; made by humans

Different greenhouse gases have different abilities to trap heat. For example, one methane molecule traps 23 times as much heat as one CO₂ molecule. One CFC-12 molecule (a type of CFC) traps 10,600 times as much heat as one CO₂. Still, CO₂ is a very important greenhouse gas, because it is much more abundant in the atmosphere.

Summary

Greenhouse gases include CO₂, H₂O, methane, O₃, nitrous oxides (NO and NO₂), and chlorofluorocarbons (CFCs).
Greenhouse gases trap heat in the troposphere. Some greenhouse gases can trap more heat than others.
Levels of greenhouse gases in the atmosphere are increasing due to human activities.

Review

What is insulation? What effect does insulation have on global temperature?
What is the greenhouse effect?
How does Earth's atmosphere resemble a greenhouse?