It is hard to gauge the number of green-collar jobs nationwide. Welders at a wind-turbine factory are viewed as having green jobs, but what about the factory’s accountant or its janitors? Workers with Sustainable South Bronx, a nonprofit group that plants vegetation to keep the area cooler and reduce air-conditioning demands, would seem to fit the bill. But so would the employees of Tesla Motors, south of San Francisco, who are producing an all-electric Roadster that sells for $98,000.

In the most-often-cited estimate, a report commissioned by the American Solar Energy Society said that the nation had 8.5 million jobs in renewable energy or energy efficient industries. And Jerome Ringo, president of the Apollo Alliance, predicted that the nation could generate three million to five million more green jobs over the next 10 years.

Green jobs are especially good “because they cannot be easily outsourced, say, to Asia,” said Van Jones, president of Green for All, an organization based in Oakland, Calif., whose goal is promoting renewable energy and lifting workers out of poverty. “If we are going to weatherize buildings, they have to be weatherized here,” he said. “If you put up solar panels, you can’t ship a building to Asia and have them put the solar panels on and ship it back. These jobs have to be done in the United States.”

Many advocates of green employment say the jobs should be good for the workers as well as the environment. Two weeks ago in Pittsburgh, more than 800 people attended a national green-jobs conference, where much of the talk was about ensuring that green jobs provided living wages. Many speakers anticipated that the jobs would do so, because they often required special skills, like the technical ability to maintain a giant wind turbine (and the physical ability to climb a 20-story ladder to work on it).

“These jobs will be better for the workers’ future, for their job security,” said Ms. Blake of the Apollo Alliance. “These green technologies are making products that the world wants, like energy-efficient buildings and light fixtures.”

Not everyone, however, is enamored with green jobs. Take the Competitive Enterprise Institute, a Washington group that opposes state mandates requiring that a certain percentage of power come from renewable sources. Myron Ebell, the institute’s director of energy and global warming policy, argues that creating green jobs often does not create jobs on a net basis.

Image RAISING THE ROOF James Wells of Sustainable South Bronx, a nonprofit group that plants vegetation in the area, working on a Bronx rooftop garden. Credit... Michael Nagle for The New York Times

“If you create jobs in wind power or ethanol,” he said, “that will take away jobs in other industries,” like building and operating conventional gas turbine power plants.