If per capita carbon emissions in China and India rose to car-happy U.S. levels, global emissions would increase by 127%, according to the International Energy Agency. If their emissions stopped at the levels found in hyper-dense Hong Kong, world emissions would go up less than 24%. As the Asian economies prosper, the United States should hope that they embrace the skyscraper more than the car, and we should reform our own policies that subsidize sprawl.
China, a manufacturing powerhouse, is already the world's biggest carbon emitter, but ordinary Chinese remain remarkably parsimonious in their energy use. Matthew Kahn, Rui Weng, Siqi Zeng and I, in a study published in 2010, estimated carbon emissions for urban households in China, measuring only household emissions and personal transportation. In our sample, the average Chinese household emitted less than 2.2 tons of carbon dioxide a year, which is less than 1/17th of the levels that Kahn and I found in an earlier study of U.S. cities. Even the greenest U.S. metro areas, such as San Jose and San Francisco, emitted almost 12 times as much as carbon as the Chinese metropolitan areas.
Our American households typically used more than 1,000 gallons of gasoline a year driving; the Chinese used about 1/100th as much gasoline. In many American cities, carbon emissions from household electricity use can top 10 tons annually, but in China, the norm was slightly more than 1 ton per year. Poor countries heat before they cool, and China heats with particularly dirty energy sources, but even there, we found that the coldest Chinese cities were emitting about as much carbon in their home heating as Los Angeles, and far less than in the parts of America with real winters.
The low carbon figures among Chinese households today mean that there is frighteningly large room for growth in Chinese energy use. The Chinese bought more than 18 million cars last year alone. India's hot climate suggests that its household emissions may eventually be even higher, once a billion air conditioners come into operation.
Massive Asian energy use raises fears of climate change, but even die-hard eco-skeptics should be anxious that soaring global energy demand will push up fuel costs.
But no one should hope that China, India and Asian nations just stay poor. Fortunately, the same cities that are providing Asia with a path from poverty to prosperity also provide an urban approach to reduced energy use.
Hong Kong is one of the richest places on the planet, with incomes roughly comparable to the U.S. and higher than much of Europe. Yet, its per-capita emissions are one-third of those in the U.S. and barely higher than China's today. Singapore is even wealthier, and its emissions are half the levels in the U.S.
As urbanists Jane Jacobs and David Owen have argued, dense urban cityscapes are not just highly productive, they are green.
Kahn and I, in our previous study of the United States, compared emissions inside and outside major cities, and found significantly lower emissions in urban cores, even holding income and family size constant. This was because dense urban areas have smaller homes and require less driving. Households in areas with more than 10,000 people per square mile use an average of 687 gallons of gasoline a year; households in areas with fewer than 1,000 people per square mile use 1,164 gallons of gas a year. The average detached home consumes 88% more electricity than the average apartment in a large building.
America's interest in promoting a hyper-urban Asia, so different from our sprawling nation, puts us in a slightly awkward position. How can a country of McMansions and Ford Expeditions preach the virtues of low-carbon urban living?
Freedom is America's greatest treasure. This includes the freedom to choose where we live — city or suburb. But we should eliminate the mistaken policies that artificially subsidize sprawl. The federal government subsidizes transportation significantly more in low-density areas than in high-density areas, and that pulls people away from cities. Economist Nathaniel Baum-Snow found in 2007 that each new postwar highway that cut into a city reduced that city's population by 18%. The home mortgage interest deduction induces people to leave urban apartments, which are overwhelmingly rented, and move to suburban homes. Because the deduction scales up with the size of the mortgage, it essentially pays people to buy bigger, more energy-intensive homes.
Reducing such policies, which push Americans away from our green cities, will enable us to make a stronger case for higher-density dwelling in India and China.
Edward Glaeser is a professor of economics at Harvard University and the author of, most recently, "Triumph of the City."