When John Edwards bowed out of the Democratic primary in January, the presidential race lost its most vocal supporter of so called green-collar jobs. His former opponents have carried the mantle forward, however-Senator Hillary Clinton in particular, who introduced an amendment to the 2007 energy bill, calling for green-collar job training.

“Green-collar” is a relatively new title. A few articles have claimed that the first usage was during congressional hearings in the 1970s. In 1991, The New York Times quoted a New York City Commissioner who complained about “green-collar fraud,” referring to companies hawking bogus environmentally-friendly products.

The term took firm root in 1999, when Alan Thein Durning wrote a book called Green Collar Jobs. But then, silence. Not until around 2006 did a handful of green-collar stories really start to pop up again, giving way to a torrent in 2007 and 2008. The press had already developed a case of green fever, showing a particular affinity for “green business” stories. Slowly, and with candidates dropping the term so often, reporters’ attention has moved down the managerial ladder, to environmentally-friendly employment.

Stories like Karen Breslau’s Newsweek piece about the growth in the green-collar job market have sprouted all over the media, adopting a variety of angles. Even local papers are digging in; last week, The Connecticut Post published an interesting piece by its Money editor, Pam Dawkins, arguing that one strength of green jobs is that they “can’t be outsourced.” On Sunday, The Mercury News in San Jose, California, published an op-ed written by a local high school teacher urging readers, “Let’s prepare valley kids to ride wave of green-collar jobs.”

If there is still any doubt that environmentally-friendly employment is a hot topic, the two remaining Democratic candidates should have laid it to rest with frequent promises that they will create five million green-collar jobs over ten years to assuage the nation’s economic and environmental woes. Last week, Clinton gave the nod to Earth Day and green jobs in her victory speech after the Pennsylvania primary.

This is all great news - we will not reduce greenhouse gas emissions unless we pay more attention to human capital in the new “green business” economy. As we’ve seen with other elements of the environmental revolution, however, there is plenty of fluff and a lot of explanation that needs to go along with lofty goals and propositions.

For starters, what is a green-collar job, exactly? The guy who installs solar panels for a living is safely in green-collar territory, but what about the engineer working at Chevron who spends half of his time on traditional, fossil-fuel energy sources and half of his time on renewables? How about the day-rate construction worker pouring concrete for a windmill farm-whose next gig is fixing the shoddy construction in Boston’s Big Dig? What about the workforce at an ethanol plant? Have those once green collars turned back to blue?

We can’t have an intelligent conversation about something if we don’t know what it is, but it might take a while to iron out the definition of a “green job.” In the meantime, it makes sense for journalists to report the lack of consensus. A good example was a New York Times article by Steven Greenhouse in March headlined, “Millions of Jobs of a Different Collar”. Greenhouse quotes three sources, with three different definitions:

• “A green-collar job is in essence a blue-collar job that has been upgraded to address the environmental challenges of our country.” [Lucy Blake, chief executive of the Apollo Alliance]

• “A green job has to do something useful for people, and it has to be helpful to, or at least not damaging to, the environment.” [Carl Pope, executive director of the Sierra Club]

• “Ten years ago, that steel was used for making low-efficiency automobiles, so those jobs were part of the dirty economy […] But now that steel is being used to build wind turbines. So now you can call them green jobs.” [Dave Foster, executive director of the Blue Green Alliance]

Keith Johnson, at The Wall Street Journal’s Environmental Capital blog, noted the same discrepancy, coming to the conclusion that “in a nutshell: ‘green-collar jobs’ can run the gamut from park rangers to Prius mechanics to physicists fiddling with nano photovoltaic research.”

Russ Juskalian is a contributor to The Observatory and a freelance writer.