The New York metropolitan area gobbles up more energy than any other major city in the world, according to a new study that aims to calculate the resources consumed in the world's largest cities.
The sprawling region that spreads into surrounding states including Connecticut and New Jersey is part of a growing number of so-called "megacities" sprouting up around the world and consuming more resources as they get larger and richer.
Now an international team of 28 researchers has partnered with the Enel Foundation, a nonprofit arm of Italian energy company Enel Group, to figure out how much electricity, fuel and water these huge cities consume, with an eye toward figuring out how some of them can cut back.
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Chris Kennedy and his colleagues compiled a list of the world's megacities, defined as metropolitan areas with more than 10 million people, most of which extend beyond official city limits.
"I like to call it a 'commutershed,' " Kennedy told CNBC. "It is the region that people will travel around in their daily lives. It is also a common labor market and housing market."
The New York "megacity" is not simply the city of 8.1 million people; it includes the 22 million people who live around the city. That jump makes a huge difference, but Kennedy says it's a more accurate representation of reality.
"What you see in Manhattan is the center, that is the piece you perceive, but the real city is the 22 million," Kennedy said.
There were eight such megacities on earth in the 1970s. As of 2010, there were 27, and that number is growing. Megacities are popping up in China and India, and toward the end of the century, the researchers expect many African megacities to rise and perhaps even surpass Tokyo in population and resource use.
Economists have already observed that larger cities tend to produce more wealth, measured in gross domestic product per person. But research has not focused as much on how urbanization and rising wealth affect resource use, Kennedy said.
The team found that cities not only produce more wealth, they also produce more waste. The world's megacities hold only 6.7 percent of the global population, but produce 12.6 percent of global solid waste, and consume 9.9 percent of global gasoline and 9.3 percent of global electricity.
"Some people have written books about New York as a kind of 'green metropolis' because there are subways and it is high density," Kennedy said. "But what we are finding is when you look at the whole megacity, we are getting a higher-than-average amount of gasoline used and electricity used, and waste produced. We think that is driven by GDP. If these cities are richer and wealthier, they are buying more, and throwing away more."
The New York City metropolitan area uses more resources than Tokyo, even though Tokyo has 12 million more people. For example, New York uses the equivalent of a supertanker of oil more than Tokyo does, every day and a half.
Much of that stems from the fact that New York is less dense than the Tokyo region and uses more fuel for transportation—both cities actually consume roughly the same amount of electricity. But the Japanese megacity has also taken some measures to improve efficiency. It aggressively worked to limit leakage from its water system—Tokyo leaks only 3 percent of its water, when most large cities leak about 20 percent.
By way of comparison, both Sao Paulo and Rio de Janeiro leak more than half of their water out of their public water system—even as both are in the midst of tremendous water shortages.
Other large cities have certain features that enable them to reduce consumption: Seoul, South Korea, has a large wastewater recycling system, and Moscow has the world's largest central heating system, which serves millions of people. London managed to reduce its per-capita electricity use from 2001 to 2010, even though its economy grew. Paris has mild weather, little heavy industry and an excellent regional rail system.
But reducing consumption or waste while maintaining economic growth is tricky, Kennedy said. In fact, megacities that consume fewer resources overall are often places where substantial portions of the population lack a basic standard of living.
Researchers already knew that as cities' economies grow, they tend to spread out, and thus they tend to consume more fuel for transportation, per person, Kennedy said.
But Kennedy's team also found that growing cities even tend to use more electricity per person. Buildings actually get bigger, because there is more space to build on, and those larger buildings use more electricity.
The team expects its list of large cities to grow longer. The Chicago area, with its 9.9 million people, fell just shy of making the cut, but it will probably be among megacities by 2020, Kennedy said.
The research, which was funded by the Enel Foundation, was published in the Proceedings of the National Academy of Sciences.