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Edward L. Glaeser

If you love nature, move to the city

By Edward L. Glaeser
February 10, 2011

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ON A pleasant spring day 167 years ago, two young men enjoyed some fishing near Concord and cooked up some chowder in a nearby pine stump. The wind spread their fire to the nearby dry grass, and the Concord Freeman reported that “as every thing around them was as combustible almost as a fireship, the flames spread with rapidity, and hours elapsed before it could be subdued.’’ By the time the sylvan inferno ended, more than 300 prime acres of Concord woodland had been destroyed.

The inadvertent tree-burner was Henry David Thoreau. Today, he is a secular saint of environmentalism, but his contemporaries understandably saw the forest destroyer as a “damned rascal’’ and “flibbertigibbet.’’ It is hard to imagine any Bostonian shopkeeper or merchant who harmed the environment as much as Thoreau.

Thoreau’s story contains a moral that remains relevant today. We are a destructive species, and if you love nature, stay away from it. The best means of protecting the environment is to live in the heart of a city.

A few years ago, environmental economist Matthew Kahn and I estimated the carbon emissions associated with living in different areas of the country. We focused on household emissions, the roughly 40 percent of American carbon emissions associated with personal transportation and home energy. We calculated energy use for households with standardized size and income, so our results wouldn’t reflect the tendency of richer people with larger families to live in the suburbs.

In much of the country, cars are the biggest carbon emitters, and density determines driving. Households in areas with more than 10,000 people per square mile average 687 gallons of gas per year, while households in areas with fewer than 1,000 people per square mile average 1,164 gallons of gas per year. Even among driving families, there is a big difference between gas usage in denser places, like Brookline, and far-flung suburbs.

In the Boston area, a standardized household drives about 1,000 miles per year, which leads to about 23,000 pounds of carbon dioxide emissions. We drive more than New Yorkers, but less than residents of less dense areas like Nashville.

We estimated that a standardized household in Boston’s urban core emits about 6,700 fewer pounds of carbon dioxide per year due to driving habits than an equivalent suburban household. Certainly, when I moved from Cambridge to a woodsy suburb, I spent endless hours in my planet-polluting Subaru. The public transportation that is more common in cities does little to balance the scales.

As for electricity use, electrical appliances account for two thirds of residential use, and summer heat explains most of the differences across the nation. Boston’s relatively mild summers mean that we use less electricity than either the South or the Midwest. Our electricity plants are also pretty green. As a result, emissions from home electricity in the Boston area run at around 9,300 pounds per year, less than one-third the level of super-humid Houston.

Boston is, however, less green because of home heating. Many Boston area residents rely on high-emission oil, rather than natural gas, for heating. The seven tons per year of carbon dioxide associated with heating a standardized household in the Boston area is higher than almost any other large metropolitan area.

There are also substantial electricity and home heating differences between cities and suburbs, mostly because suburbanites have bigger homes, even holding income and family size constant. After all, many people move to the suburbs precisely because they want a bigger home. On average, electricity use is 88 percent higher in single-family detached homes than in apartments in buildings with five or more units.

We estimate that a standardized household in a Boston suburb produces about 4,400 extra pounds of carbon dioxide per year from heating and about 1,800 extra pounds from electricity. All told, the standardized suburban household in the Boston area produces almost six tons more carbon dioxide per year than the standardized urban household.

Living around trees is less green than living around concrete. The next time you want to fight for nature, leave Walden Pond alone and start pushing for denser development in downtown Boston.

Edward L. Glaeser, a professor of economics at Harvard University, is author of “The Triumph of the City.’’ His column appears regularly in the Globe.