Difference between revisions of "Urban heat island"

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The '''Urban Heat Island Effect''' is a common observance around metropolises or cities. Essentially, because urban areas both generate and trap heat, a bubble or "urban heat island" (UHI) often forms around the city, slightly altering local meteorological observations as compared to the surrounding areas. [http://science.nasa.gov/NEWHOME/headlines/essd26apr99_1.htm] Several factors contribute to the the Urban Heat Island Effect, such as increased number of roads (asphalt can absorb and radiate heat), increased traffic, and increased industrial activity.
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One example of an occurrence of the Urban Heat Island Effect would be the metropolis of Atlanta, Georgia.<ref>It has been observed that often, with conditions held equal across the mesoscale, Atlanta will observe slightly higher temperatures (on an average of 5-8 degrees Fahrenheit) than areas further away from the center of the metropolis. [http://science.nasa.gov/NEWHOME/headlines/essd26apr99_1.htm Atlanta's Urban Heat Alters Weather Patterns], NASA </ref>
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==Urban sprawl==
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Heat islands are created through the process of urbanization. As a city grows, trees are cut down to make room for commercial development, roads, and suburban growth. Forest growth normally reduces the amount of heat and smog generated by populated areas. The materials used to build over these forests compound the urban overheating problem. Asphalt roads, tar roofs, and other dark, heat-absorbing materials hold in heat long after the sun sets, keeping the cities hotter for longer periods of time.
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Urban sprawl in conjunction with the Urban Heat Island Effect can account for the difficulties that some meteorologists have with predicting extreme short term weather events. An example of such complications is during Winter Storm events in places such as the Ohio Valley. The metropolis of Louisville, Kentucky is a sprawling urban/suburban area, while much of the surrounding area is dramatically rural in comparison. As such, it is not uncommon for Winter Storms to affect the immediate Louisville vicinity much more severely than what is actually observed within the Louisville city limits. Differences in snow totals are usually contributed to the envelope of warm air that surrounds the city, which causes much precipitation to melt into sleet or rain before it reaches the ground, reducing snowfall amounts.
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==Implications for the global warming theory==
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Warwick Hughes argues that:
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:... Atlanta, Macon and Athens were unsuitable stations to measure long-term climate variations.  Using these three stations generates a spurious warming trend in a region where there is clear evidence of long-term cooling. [http://www.warwickhughes.com/climate/atlanta2.htm]
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Citing popular literature, such as Hughes' blog, some skeptics of Global Warming attempt to attribute the global warming trend to the Urban Heat Island effect. However, there has yet to be an entry to a peer-reviewed journal that scientifically extrapolates this premise. In fact, the converse has been argued in paper submitted to credible journals such as Nature.<ref>David E. Parker, a meteorologist with the British government, has concluded that Urban Heat Island effects are most dramatic at night, but their overall effect on global climate patterns is neglible [http://www.nature.com/nature/journal/v432/n7015/abs/432290a.html Climate: Large-scale warming is not urban], Met Office </ref>
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==Notes==
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<references/>
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==External links==
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*[http://www.warwickhughes.com/climate/atlanta2.htm Reviews of station by station claimed IPCC global warming, urban heat island effects in global warming data]
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*Parker, David E., David M. Sexton, and Chris K. Folland. Great Britain. Hadley Centre for Climate Prediction and Research. Met Office. [http://www.metoffice.gov.uk/research/hadleycentre/pubs/HCTN/HCTN_46.pdf Natural and Human Influences on Central England Temperature]. January 2004.
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[[category:meteorology]]

Revision as of 09:12, 17 October 2007

The Urban Heat Island Effect is a common observance around metropolises or cities. Essentially, because urban areas both generate and trap heat, a bubble or "urban heat island" (UHI) often forms around the city, slightly altering local meteorological observations as compared to the surrounding areas. [1] Several factors contribute to the the Urban Heat Island Effect, such as increased number of roads (asphalt can absorb and radiate heat), increased traffic, and increased industrial activity.

One example of an occurrence of the Urban Heat Island Effect would be the metropolis of Atlanta, Georgia.[1]

Urban sprawl

Heat islands are created through the process of urbanization. As a city grows, trees are cut down to make room for commercial development, roads, and suburban growth. Forest growth normally reduces the amount of heat and smog generated by populated areas. The materials used to build over these forests compound the urban overheating problem. Asphalt roads, tar roofs, and other dark, heat-absorbing materials hold in heat long after the sun sets, keeping the cities hotter for longer periods of time.

Urban sprawl in conjunction with the Urban Heat Island Effect can account for the difficulties that some meteorologists have with predicting extreme short term weather events. An example of such complications is during Winter Storm events in places such as the Ohio Valley. The metropolis of Louisville, Kentucky is a sprawling urban/suburban area, while much of the surrounding area is dramatically rural in comparison. As such, it is not uncommon for Winter Storms to affect the immediate Louisville vicinity much more severely than what is actually observed within the Louisville city limits. Differences in snow totals are usually contributed to the envelope of warm air that surrounds the city, which causes much precipitation to melt into sleet or rain before it reaches the ground, reducing snowfall amounts.

Implications for the global warming theory

Warwick Hughes argues that:

... Atlanta, Macon and Athens were unsuitable stations to measure long-term climate variations. Using these three stations generates a spurious warming trend in a region where there is clear evidence of long-term cooling. [2]

Citing popular literature, such as Hughes' blog, some skeptics of Global Warming attempt to attribute the global warming trend to the Urban Heat Island effect. However, there has yet to be an entry to a peer-reviewed journal that scientifically extrapolates this premise. In fact, the converse has been argued in paper submitted to credible journals such as Nature.[2]

Notes

  1. It has been observed that often, with conditions held equal across the mesoscale, Atlanta will observe slightly higher temperatures (on an average of 5-8 degrees Fahrenheit) than areas further away from the center of the metropolis. Atlanta's Urban Heat Alters Weather Patterns, NASA
  2. David E. Parker, a meteorologist with the British government, has concluded that Urban Heat Island effects are most dramatic at night, but their overall effect on global climate patterns is neglible Climate: Large-scale warming is not urban, Met Office

External links