Chapter 2
The Earth's Global Energy Balance

Chapter Overview

Electromagnetic radiation is the primary focus of Chapter Two. Practically all environmental processes active at the earth's surface can be traced back to the receipt of solar radiation. However, the energy available to drive environmental processes is unequally distributed across the globe. Sun angle affects the intensity of energy received at a location. Clouds reflect and scatter solar radiation thus reducing insolation received at the surface. The reflectivity of the surface also determines how much insolation can be absorbed. Large energy inputs to low latitudes yields a region of energy surplus while high latitude locations suffer from energy deficits. The earth's global atmospheric and oceanic circulation systems work to redistribute this energy to maintain a global energy balance.

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Key Concepts

• Electromagnetic radiation is a form of energy emitted by all bodies in the form of waves.
• The hotter the body the shorter the wavelength of emission and the more energy it will emit.
• The sun emits most of its energy as shortwave while the earth emits longwave radiation.
• The intensity of solar energy is strongest in the visible wavelengths.
• Over the long term, solar energy absorption is balanced by longwave energy emission from the earth.
• The angle of the sun's rays determines the intensity of insolation. The larger the angle, the higher the intensity.
• The seasonal pattern of insolation serves as the basis for dividing the globe into latitudinal zones.
• Ninety nine percent of the earth's atmosphere is composed of two gases, nitrogen and oxygen.
• Carbon dioxide and water vapor are good absorbers of longwave radiation and re-emit the energy as counterradiation thus contributing to the greenhouse effect.
• Ozone is found primarily in the stratosphere and absorbs UV light.
• Sensible heat is the quantity of heat held by a body and can be sensed by touching or feeling and moves by conduction between objects.
• Latent heat is energy that is stored during evaporation of water and released during condensation.
• Clouds scatter incoming solar radiation to create diffuse radiation.
• The absorption of radiation by the earth depends on the surface's albedo or reflectivity. Albedo is largely determined by surface color and sun angle.
• As incoming energy exceeds outgoing, a net radiation surplus exists between 40 degrees north and 40 degrees south latitude.
• Poleward of 40 degrees north and 40 degrees south latitude outgoing energy exceeds incoming energy.
• The earth's global atmospheric and oceanic circulation enables poleward transport of energy to address this imbalance.

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Key Terms

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Web Links

The Earth's Radiation Balance (Dr. Steve Ackerman, Space Science and Engineering Center, University of Wisconsin, Madison)

This site provides access to several good images and animations as well as background information about the earth's radiation balance. Sponsored by Cooperative Institute for Meteorological Satellite Studies, Space Science and Engineering Center, University of Wisconsin - Madison.

Visualizing the Differences Between Seasons

Visualizations of the seasonal difference in insolation, surface temperature and net radiation can be viewed at this Learning Through Collaborative Visualization Project sponsored site.

Ozone Depletion Resource Center (United States Environmental Protection Agency)

This site has links to ozone deletion resources of interest to the general public. Use the UV Index to protect yourself from the sun's ultrviolet radiation, see what individual action you can take to protect the ozone layer, or read about the environmental indicators of ozone depletion.

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