Why Skyscrapers Can Be Green

Occasionally, I catch sight of the San Jose skyline. It's hard to do because it doesn't amount to much. Height restrictions limit how tall buildings in San Jose can be built. Some of the restrictions conform to FAA (Federal Aviation Administration) regulations because part of downtown lies in flight path of nearby airport, but they doesn't apply to all of San Jose (or even all of downtown San Jose). No doubt, some of the height restrictions are due to the well-intentioned efforts by some to keep San Jose beautiful, to keep it green, assuming that buildings that reach to the heavens are bad for the environment. That, however, is a mistaken assumption.

When you prevent developers from building up, they don't stop building. Instead, they build out, which leads to more urban sprawl, longer commutes, increased congestion, and less green space. People who live in high rises also tend to live in smaller dwellings than do those of us who live in the suburbs and in the country, which is why the carbon footprint of high rise urbanites are, on average, smaller than suburban and country dwellers (and why skyscrapers are green). As economist Ed Glaeser puts it ("Why Cities Rock"):

Together with Matthew Kahn, I’ve assembled data on carbon emissions associated with living in different parts of the country. And there are two facts, which I think are important, to come out of that. One of which is that people who live in cities do tend to emit significantly less carbon than people who live in the country, and this is controlling for income and controlling for family size. That’s coming mainly from driving, from the fact that there’s just a lot fewer carbon emissions associated with dense living. It’s not just the move to public transportation; it’s also the drivers within cities — they’re just driving much shorter distances. And then, of course, it’s because of much smaller homes. The higher price of urban space means that people are living in smaller homes, even with the same family size. And that leads to lower electricity usage, lower home heating usage — and those are the facts that I think make cities seem, at least to my eyes, significantly greener.

This is illustrated in the following table, which lists the difference in cost of living in the suburbs as compared to the city center in 10 U.S. cities. These are taken from a paper by Glaeser and Kahn ("The Greenness of Cities: Carbon Oxide Emissions and Urban Development") where you can find the complete table (Table 5) that compares 48 metropolitan areas:

The first column presents the difference in CO2 emissions caused by driving between those who live in the suburbs and those who live in the city; the second lists the difference caused from using public transportation between those who live in the suburbs and those who live in the city; the third, heating; the fourth, electricity; the fifth, total difference; and the sixth, the total translated into $s. What the table shows, for example, is that people living in the suburbs of NY contribute 6,150 more pounds of CO2 emissions from driving than someone living in the city center; 2,367 fewer pounds from using public transportation; 5,650 more from heating their homes; and 4,015 more from using electricity in their homes. While there are a few exceptions, of the 48 metropolitan areas analyzed by Glaeser and Kahn, city dwellers emitted far less carbon emissions than did their suburban counterparts.

Does this mean that everyone should (or wants to) live in high rises located in city centers? Of course not. There's a lot to be said for the suburban life where you can play catch in your front yard and take evening strolls around your neighborhood. Even a city-promoter like Ed Glaeser moved to the suburbs when he and his wife had kids. But that doesn't mean we should adopt policies that incentivize people to move to suburbia when they wouldn't otherwise do so. As Glaeser notes ("Why Cities Rock"):

What I’m arguing against is policies like artificially subsidizing home ownership, like artificially subsidizing highways, and like our very difficult problem of local schooling that are pushing people into suburbs. I’m just arguing that people should be free to choose without government policies that... vastly bias the decision against urban life... 

What I’m championing is rethinking those barriers to building that would enable places where the market demand is there, where there are people that actually want to live in high-rise apartments, I’m championing, eliminating the barriers that stop that from happening. I’m not championing anyone who… loves his quiet, rural area, and saying that gosh we want to shoehorn this person into an apartment. Obviously some people don’t want that, and that’s terrific. It’s wonderful that the market can deliver lots of different living styles.

On a related note, skyscrapers are greener in more temperate climates than they are in climates that are less so. It's greener to build high rises in metropolitan areas like San Francisco and San Jose than in Houston or Memphis. This can be seen in the following graphs (also from the paper by Glaeser and Kahn), which plot energy consumption by average January and average July temperatures, respectively. The first graph illustrates that energy consumption in January is much lower in metropolitan areas where temperatures are higher, and the second graph shows that energy consumption in July is much lower in metropolitan areas where temperatures are lower. The key to lower consumption, in other words, is to build in cities that are neither too hot in the summer nor too cold in the winter.

Unfortunately (at least for the environment), current land-use regulations often make it harder to build in metropolitan areas located in temperate climates than to build in in less temperate ones. And many of these regulations are the result of well-meaning campaigns run by environmentally-conscious individuals concerned about the environmental impact of various development projects. However, when thinking about the environmental impact of proposed development projects, not only do we need to think about their local environmental impact but also their global environmental impact. Just as preventing contractors from building up doesn't prevent them from building out, limiting construction in one part of the country doesn't stop it from happening. It simply moves to another part of the country (or world).  Does this mean that we should scrap all land-use regulations? No, but we need to be smarter about them ("Why Cities Rock"):

Now, you’d think then that if you were interested in reducing America’s entire carbon footprint that people in California would be championing, championing new development in high rises around San Francisco Bay. These areas are by far the lowest carbon related areas in the country, and if you built lots of high rises in these attractive areas where there’s significant demand, you would significantly reduce our overall carbon footprint. Yet, unfortunately, there’s been I think something of a mistake. People have looked at their local situation and thought that by stopping a building they were making things greener. But that’s not really how things work, because if I turn off the spigot of housing in coastal California, it turns on somewhere else. It turns on in the desert outside of Phoenix, it turns on in Houston. And the place where the new building is going on is almost surely going to be more carbon intensive than coastal California. So implicitly by pushing development away from California, many environmentalists have actually increased carbon emissions for the country as a whole.

All of this and much more is the subject of Ed Glaeser's somewhat recent book, Triumph of the City: How Our Greatest Invention Makes Us Richer, Smarter, Greener, Healthier, and Happier. His research was also the subject of a 2011 Freakonomics podcast ("Why Cities Rock"), which can be downloaded from iTunes or listened to at the Freakonomics website (where you can also find the transcript of the interview). It's only 17 minutes long and well worth one's time.