With the next Democratic primary being held in Pennsylvania on Earth day, we turn our attention today to “green collar jobs.” While there is certainly no one-size-fits-all panacea for the nation’s struggling industrial cities, proponents of the movement see wide ranging benefits from creating a new economy around environmental awareness.

What exactly constitutes a “green collar job” and whether its a viable economic solution are still a matter of debate and probably will be for some time. Is a job at a plant that only provides the steel for wind turbines a green job? Does an engineering job at a solar energy company warrant the title green collar? Others question whether these jobs are as secure and pay as well as supporters claim.

Some even see this all as a way to avoid talking about the environment on its merits alone. In the Pittsburgh Post-Gazette, Don Hopey writes that the candidates have “mentioned high fuel prices and alternative energy sources — mainly wind power and bio-fuels — but couched them as pocketbook issues or ‘green collar’ job generating new industries.”

Still, such questions haven’t stopped advocates from pushing to get the idea on the national agenda. With possible benefits as large and varied as slowing global warming, revitalizing the economy, and reducing dependence on foreign oil; policies that encourage government support for the creation green businesses must be explored, they say.

The “Good Jobs, Green Jobs“ national conference, held in Pittsburgh last month, represents milestone of sorts for the movement. The conference brought together hundreds of government officials, activists and corporate representatives to discuss how America’s cities can climb out of poverty through green jobs.

“The movement to make American cities more sustainable, efficient and livable is perhaps the greatest new engine for urban economic growth, innovation, and job creation in decades,” said Phil Angelides, chairman of the board of directors for the Apollo Alliance, one of the conference’s conveners.

The message is not lost on the Democratic candidates for president, both of whom purport to be on board with the concept and include it in their platforms.

Indeed, Barack Obama outlined his plan to create 5 million green jobs a month before the conference, although he he generally doesn’t refer to them as “green collar.”

But Hillary Clinton is wont to point out that she proposed the 5 million job creation goal first, back in November.

As such, the New York senator outlined her plan a couple days later. Although the numbers were mostly geared towards Maryland, she expanded on details that had generally been pretty vague.

However, her projections for the number of jobs she will create changes from time to time. Clinton had generally estimated that her Green Building Fund will create 50,000 green collar jobs, but has recently boosted that number to 100,000, although not in all statements.

In response to Clinton’s attack on Obama’s proposal, the Illinois senator’s campaign noted that he actually gave a speech in October – a month before her – saying he would create “millions” of green jobs.