NCPA - National Center for Policy Analysis

Urban Heat Islands

March 4, 2004

An unprecedented rise in carbon dioxide levels occurred 8,000 years ago, according to the University of Virginia, just about the time when humans begin raising livestock and clearing forests for agriculture. Research shows:

  • Levels of methane -- a powerful, yet less prevalent greenhouse gas -- increased 5,000 years ago with the flooding of rice fields and increasing herds of livestock.
  • Ice samples show that the atmosphere has experienced patterns of warming and cooling as far back as 400,000 years ago, long before human influence of the atmosphere.
  • The rising level of methane that occurred 5,000 years ago probably staved off a period of cooling, preventing another ice age.

In addition to the evidence that supports the theory that there have been periods of warming and cooling for thousands of years even without human activity, scientists also dispute the accuracy of current ground-based temperature readings used to support the theory of global warming.

The American Geophysical Union's recent study shows:

  • Temperatures in urban areas such as Atlanta and Houston are artificially raised by as much as 10 degrees in the summer due to concrete and concentrations of human activity.
  • Known as the "urban heat island effect," these temperature readings reflect increases due to localized population growth in specific areas, but do not represent an overall increase in global temperatures.
  • The "urban heat island effect" can artificially raise temperatures in towns as small as 1,000 people.

Sources: James M. Taylor, "Greenhouse Gases Staved Off Ice Age," and "New Study Confirms Dramatic Urban Heat Island Effect," Environment and Climate News, February 2004, Heartland Institute.


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