The Greenhouse Effect



 

Learning Objective

  • Recall the causes of global warming and how humans have aggravated the phenomenon.

Key Points

    • Solar radiation is absorbed at the Earth’s surface and emitted as thermal energy that can be re-absorbed by greenhouse gases.
    • Greenhouse gases include water vapor, carbon dioxide, ozone, and methane; the major components of atmospheric gas—nitrogen, oxygen, and argon—are transparent to infrared radiation.
    • The greenhouse effect insulates the Earth’s surface, making it hospitable to life; however, human activities have increased the concentration of these gases, causing global warming.

Terms

  • greenhouse gasesgases such as water vapor, carbon dioxide, ozone, and methane that absorb and trap heat as it tries to escape from the Earth’s atmosphere
  • global warminga rapid increase in temperatures; caused by greenhouse gases trapping extra heat in the atmosphere; it may produce a number of environmental consequences
  • greenhouse effectan elevation in surface temperatures due to atmospheric gases absorbing and re-radiating thermal energy

While about 30 percent of the solar radiation directed at the Earth scatters at the outer atmosphere, the remainder is either absorbed by clouds and atmospheric gases or is transmitted to the Earth’s surface. The energy that reaches the Earth’s surface is absorbed and subsequently reflected back into the atmosphere in the form of infrared radiation, as shown in the diagram below. This thermal radiation from the surface has a much longer wavelength than the solar radiation that was initially absorbed.

The greenhouse effectA summary of the heat transfer in the Earth’s atmosphere.

The majority of gases in the atmosphere, such as nitrogen, oxygen, and argon, cannot absorb this infrared radiation. Gases known as greenhouse gases, including water vapor, carbon dioxide, ozone, and methane, absorb and trap this heat as it tries to escape from the atmosphere. Greenhouse gases then re-radiate this energy back to Earth, elevating atmospheric temperatures even when the surface is not being directly irradiated by the sun. The cloud layer can also absorb infrared radiation and contribute further to the greenhouse effect.

Without this trapping effect, it is estimated that the surface of the Earth would be approximately 30 degrees cooler than current temperatures. The greenhouse effect modulates the temperature at the Earth’s surface and makes it hospitable to life.

Human activities have increased greenhouse gas concentrations n the atmosphere through the combustion of fossil fuels, release of methane from farms, industrial emissions, and deforestation. This increase in greenhouse gases is producing the phenomenon known as global warming, a rapid increase in atmospheric temperatures that may produce a number of environmental consequences, such as more extreme weather.