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Battery Park
When summer temperatures rise to uncomfortable levels, cities take a bigger beating than the rest of the landscape. This urban heat effect is especially brutal in big, dense, concrete-dominated cities like New York.
Armed with a thermal imaging camera that detects infrared radiation, artist Nickolay Lamm spent the afternoon in NYC capturing the city's heat signatures on August 15, 2013. The results are a compelling illustration of why it feels like you might melt there in the summer.
"The general message is that manmade surfaces tend to be warmer than natural surfaces," said atmospheric scientist John Frederick of the University of Chicago, who studies energy budgets of various types of surfaces. "This has implications for energy demand (and people’s individual electricity and natural gas bills). In summer, the heat island effect will increase the demand for cooling, and in winter the same effect reduces the demand for heating."
The complex temperature structure of urban settings shows up clearly in the thermal image above, Frederick says. The trees in Battery Park, whose leaves can cool by transpiration, have the coldest temperatures an appear blue. A black lamppost that absorbs sunlight efficiently is hot and red, while building materials display a range of temperatures depending on their thermal properties and exposure to the sun.
Compare the thermal image to the one at the right. The warm brick wall of the building on the left shows up bright pink, while the windows are green because they are in contact with an air conditioned interior, and remain cooler than the wall. The vertical walls provide added area for absorption of solar radiation and increase urban heating in their immediate vicinity, while vegetation can provide cooling to offset the urban heat island effect, Frederick says.
The thermal image below shows the impact that light and dark colors have on heat absorption. Dark surfaces contribute to the urban heat island effect, while white surfaces have the opposite effect, Frederick says. The white stripes of this crosswalk reflect sunlight and are cooler (yellow, orange) than the street’s dark surface (red). Contact with the air below street level apparently keeps the sewer grate relatively cool (green).
White roofs and light-colored walls will reflect more solar radiation and remain cooler than dark surfaces. But, solar radiation provides only part of the heating, Frederick says. The atmosphere also generates longwave infrared radiation, which is a major factor.
"If we had eyes that responded to longwave infrared radiation, the world would look very different," Frederick said. "It would remain bright 24 hours per day since the longwave radiation emitted by the objects around us is always there. Since the longwave radiation is invisible to us, most people do not realize how important it is in determining the temperature of the Earth’s surface and as a mechanism for objects to lose energy and cool themselves."
Metallic surfaces are better at reflecting the longwave part of the spectrum. This is probably why the Empire State sign in the image to the left appears dark and cool. In most cases, reflected energy leaves the immediate environment and ends up being dissipated in the atmosphere or even escaping into space.
But in a densely built urban area, both the solar energy reflected and longwave energy emitted by one surface could be absorbed by other surfaces and cause heating. This leads to a “radiation trapping” effect in urban canyons where tall buildings are densely packed, Frederick says. This effect is probably common in New York City.
Check out the rest of the hot city in more of Lamm's photos on the following pages. And keep in mind that he took these images on an average August afternoon when termperatures maxed out around 83 °F, an unpleasant level as any New Yorker will tell you, but far from the record of 97 °F.
All photos: Nickolay Lamm / StorageFront.com.
The complex temperature structure of urban settings shows up clearly in the thermal image above, Frederick says. The trees in Battery Park, whose leaves can cool by transpiration, have the coldest temperatures an appear blue. A black lamppost that absorbs sunlight efficiently is hot and red, while building materials display a range of temperatures depending on their thermal properties and exposure to the sun.
Compare the thermal image to the one at the right. The warm brick wall of the building on the left shows up bright pink, while the windows are green because they are in contact with an air conditioned interior, and remain cooler than the wall. The vertical walls provide added area for absorption of solar radiation and increase urban heating in their immediate vicinity, while vegetation can provide cooling to offset the urban heat island effect, Frederick says.
The thermal image below shows the impact that light and dark colors have on heat absorption. Dark surfaces contribute to the urban heat island effect, while white surfaces have the opposite effect, Frederick says. The white stripes of this crosswalk reflect sunlight and are cooler (yellow, orange) than the street’s dark surface (red). Contact with the air below street level apparently keeps the sewer grate relatively cool (green).
White roofs and light-colored walls will reflect more solar radiation and remain cooler than dark surfaces. But, solar radiation provides only part of the heating, Frederick says. The atmosphere also generates longwave infrared radiation, which is a major factor.
"If we had eyes that responded to longwave infrared radiation, the world would look very different," Frederick said. "It would remain bright 24 hours per day since the longwave radiation emitted by the objects around us is always there. Since the longwave radiation is invisible to us, most people do not realize how important it is in determining the temperature of the Earth’s surface and as a mechanism for objects to lose energy and cool themselves."
Metallic surfaces are better at reflecting the longwave part of the spectrum. This is probably why the Empire State sign in the image to the left appears dark and cool. In most cases, reflected energy leaves the immediate environment and ends up being dissipated in the atmosphere or even escaping into space.
But in a densely built urban area, both the solar energy reflected and longwave energy emitted by one surface could be absorbed by other surfaces and cause heating. This leads to a “radiation trapping” effect in urban canyons where tall buildings are densely packed, Frederick says. This effect is probably common in New York City.
Check out the rest of the hot city in more of Lamm's photos on the following pages. And keep in mind that he took these images on an average August afternoon when termperatures maxed out around 83 °F, an unpleasant level as any New Yorker will tell you, but far from the record of 97 °F.
All photos: Nickolay Lamm / StorageFront.com.
