Urban heat island: Global threat or environmental myth

Threat

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by Tabren Wyldstar

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In recent time scientists have tried to answer the age-old question about whether the legendary "urban heat island" actually exists. Reading over their "findings" I find myself pondering whether their research is valid.

The experience for most city dwellers is that the urban heat island is a real phenomena and not imaginary. Frequently weather reports will give one expected high for the suburbs of a given city and a higher temperature for the expected high in the downtown region. This anecdotal evidence is compelling, but hardly scientific.

According to available information, scientists have attempted to use data gathered from weather recording stations in and around urbanized regions (IE cities) and thermal scans from Earth orbit to measure the thermal "footprint" of cities, attempting to validate or debunk the existence of urban heat islands. Their findings pointed toward debunking the issue, however, I find several things wrong with their tests.

First, most weather recording stations are located within parks and other "green" regions, ostensibly to prevent contamination of their readings from adjacent buildings. The problem here is, most such facilities are far enough away from the central districts to render their readings unusable or immaterial to the question at hand and being in a "green" zone would lower the temperature effect one is attempting to measure.

Second, specific to the thermal "footprint" scan, the test was done during the night, after the buildings would have been cooled internally by artificial air conditioning and well after the pavement in the city would have cooled. Again, this negates in part (if not entirely) the relevance of their findings.

I propose a rethinking of the term "urban heat island" to better account for and understand its existence and environmental impact.

Traditionally the urban heat island effect has been thought to be caused by heat building up in the walls of buildings and in the pavement around the buildings. Although this sounds feasible and is somewhat correct, it completely misses understanding the true cause: a lack of vegetation in the affected areas. In undeveloped or lightly developed regions the trees and plants of the region absorb solar energy and transform it through photosynthesis into stored chemical energy. Within urbanized environments this energy is instead stored as heat in the buildings and pavement and begins rapidly dissipating when the solar energy of the day is taken away at sunset.

Recent support for this idea cropped up in a surprising manner. NASA, changing its method of temperature measurement, noted that some of the warmest years in the past century have not been in the last few decades, but during the 1930s. This was the dust bowl era, marked by windstorms that swept Colorado and Kansas topsoil downwind as far away as New York City and Boston. The grass and trees of the mid-west withered from lack of water. For all intents and purposes the fields of Colorado, Kansas and Oklahoma became one enormous paved surface, devoid of meaningful vegetation.

A secondary source of heating comes from the vehicles we use to move about the city. Our cars and buses not only contribute terrifying amounts of carbon dioxide and carbon monoxide into the environment, but also contribute significant amounts of thermal pollution. This effect is most apparent during the day when we humans are out and about our daily activities. Since a large percentage of our vehicles travel from the dispersed suburbs into the heart of the city, these mobile heat sources accumulate quickly in our downtown regions, adding their heat emissions to the microclimate of the city. At night when we return to the suburbs, this heat is again distributed over a larger area and becomes more manageable by nature.

The urban heat island effect is more pronounced during winter months in northern cities. Prior to urbanization accumulated snow would reflect considerable solar energy back into space. With the proliferation of pavement in our cities, heat is retained longer, causing lower accumulated snow levels on pavement and allowing them to clear more rapidly. Once the snow is melted the pavement once again begins absorbing heat from solar energy.

Additionally we humans tend to clear the pavement of snowfall immediately or shortly after it accumulates on pavement surfaces (streets and sidewalks). This is primarily to allow safe travel between points in our city to keep our local economy operational, even after a major snowfall. An unintended consequence is the allowing of pavement to once again begin heating up from solar energy instead of that energy being reflected away by the blanket of snow.

To summarily dismiss the urban heat island effect because of night-time temperature scans or temperature readings taken mostly from park areas is not, in my book, good science. Nor is it good science to blame the buildings and pavement alone. Like most issues the causes and sources of urban thermal pollution are diverse. Research into the issue must take into the equation the entire environment that might affect the issue, including the effects mankind itself has on the issue.

When we change our perspective, mankind's responsibility in such matters becomes ever clearer. Yes, the buildings and pavement contribute to the urban heat island, but one does not blame the gun when a killer murders an innocent. We begin building the urban heat island not with the laying of a foundation or paving of a road, but by cutting down the forest and plowing under the grass to prepare the Earth for our constructs. What does that tell you about how we must reverse the environmental crisis that is looming on the horizon?

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