Americans put themselves on the path to green careers.

Kathleen Loa first began thinking about pursuing a green career while she was a student at Oberlin College. Now, armed with a degree in chemistry, she is taking the first step in that direction. She’s serving as an intern at the nonprofit Alliance to Save Energy in Washington, D.C. After earning a master’s in energy policy, she’ll find a job.

“I want to keep working on environmental energy, either through a nonprofit role or a for-profit company,” says Ms. Loa of Claremont, Calif.

That goal puts her in the vanguard of one group seeking eco-friendly jobs – students and recent graduates who hope to join the green boom at the beginning of their careers. A second group includes people in midcareer who want to parlay their current skills into green jobs.

“It’s an exploding field,” says Matthew Wheeland, managing director of GreenBiz.com. “It can be anything from a very technical job of manufacturing solar panels to the sustainability officer of a Fortune 500 company.”

Yet defining just what constitutes a green job remains a challenge.

“A lot of groups around the country are thinking about green jobs, but there’s no clear consensus about what they are,” says Julian Alssid, executive director of the Workforce Strategy Center in New York. Nor are there reliable figures about the number of green positions.

Some eco-friendly jobs are newly created. Others require new skills for existing jobs. “I kind of chuckle when people talk about green jobs,” says Richard Stuebi, a fellow at The Cleveland Foundation in Ohio. “In many ways they look like traditional jobs, just repositioned to sustainable products and services.”

As one example, he points to the burgeoning demand for machinists, fabricators, and welders associated with wind turbines. “That’s now being called a green job,” Mr. Stuebi says. “But the job itself doesn’t look a whole lot different from those in the auto industry 20 years ago. Solar-panel installers are doing a lot of the same things electricians and roofers have done – running wire, drilling holes in roofs. And people who can operate cranes and do onsite pouring of concrete can erect and install wind turbines.”

Some eco-friendly positions deal with energy efficiency in residential and commercial buildings and in transportation. Others involve energy generation, such as wind turbines and solar power. Industries offering green careers range from utilities and construction to manufacturing.

Energy auditors and air-quality auditors represent key emerging occupations. Energy auditors identify cost-effective investments that owners and tenants can make to reduce heating and air-conditioning bills.

Legal services offer other green opportunities. These range from helping companies create voluntary carbon programs to assisting with contracts for green real estate developments, says Larry Ostema, an attorney with Horack Talley in Charlotte, N.C.

“In the last 12 months, there has been an explosion of firms advertising the abilities of their lawyers to assist clients with issues associated with climate change,” says Mr. Ostema, who heads his firm’s Green Initiatives group.

For students like Loa, business schools, law schools, and technical institutes offer degrees with green components. “Our goal is to develop graduates who can bring creative solutions to environmental problems,” says Robert Krueger, director of environmental studies at Worcester Polytechnic Institute in Massachusetts.

“More graduates are looking to make a difference,” says Mitch Baranowski, principal of BBMG, a branding firm in New York that works with green clients. “More than ever, that set of young people cares about doing right by people and the planet. We don’t have enough openings for the number of interested parties we get.”

Marie Kerpan, founder of Green Careers in Mill Valley, Calif., counsels midcareer professionals who want to switch to a green career. “They have concerns about global warming and sustainability, and want to align their values with their work,” she says.

Most midcareer applicants do not go back to school, says Ms. Kerpan, who teaches a green MBA program at Dominican University in San Rafael, Calif. “They can make a direct transfer into a green career. Sometimes it’s applying their skills and experience to a company that has a green product or service or operates with green values.”

Some go into public office – city council or sustainability planner in local government. Others start their own business, such as a green wedding planner. Or they join an existing firm. One green MBA graduate became the sustainability director at a local community bank.

Sometimes another kind of green becomes an issue. “If a $150,000 marketing executive wants to make the same amount of money [in a green job], that’s tough,” Stuebi says. “Most of these companies are relatively small, at a high-growth stage, and don’t have the money to pay high salaries.”

Other recruiters say certain green fields find a shortage of workers. “There’s not a whole lot of human capital out there with experience in clean-tech or sustainable clean technology,” says Andy Zaleta, a partner at Battalia Winston, an executive search firm in Boston. “If we have to find a CEO or a COO for a fuel cell company, there are just not a lot of people to choose from.”

Geoffrey Castro, executive director of an environmental nonprofit organization in Houston, wants to parlay his six years in the nonprofit environmental field into a green corporate job.

The search is slow. A major website for green jobs listed only one position in Houston.

“These positions are not as pervasive down here in the oil-and-gas corridor,” he says.

For those seeking green careers, either at an entry level or as a career change, Mr. Zaleta offers this advice: “Networking, networking, networking.” He notes that 85 percent of people find jobs that way, while only 10 to 12 percent use job placement firms. He suggests alumni associations, energy associations, and clean-energy conferences as possible resources. Some applicants also turn to green-career websites.

Whatever strategies job hunters use, Kerpan says, they must become educated in the green economy. Calling green careers “solutions to mega-problems,” she adds, “We’re already seeing exponential growth. I don’t see any end to this. One can’t even imagine a more dramatic shift in consciousness. It’s going to affect everything. It’s the work of our time.”