Developing a hotter L.A.

High-density development can create ‘urban heat islands’ that may add to global warming.

Los Angeles’ accelerating quest to create centers of higher population density — especially downtown, in Hollywood and in Mid-Wilshire — may be on a collision course with California’s crusade to slow global warming by reducing its greenhouse gas emissions. And the potential trouble comes from an unlikely source — buildings.

High-density development is usually considered environmentally friendly if it occurs near subway, rail or bus lines, and people can abandon their cars to get around. But unless people actually do take advantage of public transit and reduce their energy consumption, the environmental costs may outweigh the benefits.
One effect of high-density development that can potentially increase energy consumption is a phenomenon known as the “urban heat island.” This is principally caused by the construction materials — brick, concrete, asphalt, stone and other substances — used most often in building central cities. Because these materials retain heat and cool slowly, they raise the ambient air temperature and make central cities a few degrees warmer than rural and suburban areas. For instance, the temperature difference between Phoenix and its outlying areas can be upward of 10 degrees. The difference is even more pronounced at night because rural and suburban areas have fewer buildings, less concrete and asphalt and more vegetation, and thus cool faster.

Packing taller residential buildings closer together to increase density, without making room for significant areas of green space, such as parks or shaded plazas, only worsens the effect.

This is not an earth-shattering revelation. Researchers have known about the effect of the urban heat island on ambient air temperature for more than 100 years.More recently, however, heat-island studies of such cities as London, Athens, Tokyo, Beijing, Phoenix and Los Angeles have not only shown the problem worsening but have documented the rising level of energy consumption associated with it. The greater the density and the less green space nearby, the more severe the urban heat island can become.

Current research does not suggest that urban heat islands directly contribute to global warming. But they may be a factor in another way. The amount of greenhouse-gas-producing energy needed to operate buildings — heating, cooling and lighting them — makes up a significant portion of our overall energy consumption. Any phenomenon that increases the urban heat island effect — such as more high-density development without consideration for green space and energy efficiency — could potentially result in still-higher energy consumption and greenhouse gas emissions, primarily because of the greater use of air conditioning.

Just how much energy do buildings consume?

Los Angeles Times