The promise of the green economy and the clean-tech revolution is that they will bring a new wave of job opportunities - productive and respectable jobs at every part of the economic spectrum, from line workers to senior managers. Nonprofit groups like the Apollo Alliance have made this part of their raison d'etre. A steady drumbeat of studies since the late 1990s has told us that burgeoning markets for solar, wind, clean transportation, and other technologies would represent the next big wave of job creation. Cities and states have been positioning to become clean-tech hubs, eyeing the workforce development potential. Organizations representing low-income populations have been viewing the green economy as an entry point for those near the bottom of the economic ladder.

So, now that clean technology and the greening of business seem to be in full swing, where are all the jobs? So far, they're nowhere in sight - at least not in any appreciable numbers.

The reasons are many and varied. Most of the big companies in the clean-energy business - the BPs, GE, and PG&E's of the world - don't seem to be going on hiring sprees, typically creating clean-tech business units from within. So, too, with much of the green business activity - it has to do with efficiency, with doing more with the same or fewer resources, and that includes human resources. Few of the start-ups are undergoing massive hiring, and when they do, they're more often in the market for engineers and other skilled professionals. And the jobs that are being created are disperse, geographically, meaning that there are few robust Silicon Valley-like clean-tech clusters, where companies congregate and jobs proliferate.

Despite such obstacles, there seems to be new energy building behind the notion of a Big Green Job Machine. Last week in Pittsburgh, for example, a Good Jobs, Green Jobs conference, organized by the Sierra Club and the United Steelworkers union, drew more than 900 people from business, government, nonprofits, academe, and labor unions to share strategies for increasing job opportunities in the environmental and clean-tech sectors.

There were about 8 million green jobs in the U.S. in industries that attracted $148 million in investment in 2007, up 60 percent from the year before, Lois Quam, managing director of alternative investments at Piper Jaffray, told the conference. I haven't yet seen the research on which this was based, but I'm intrigued. As I noted in our State of Green Business report, tracking green job creation has been difficult. One reason is that green jobs, at least by my definition, aren't often identified as such, and can be found throughout companies of all sizes and sectors. Does a procurement manager - whose job entails implementing her company's environmentally preferable procurement mandate, thereby seeking out and purchasing millions of dollars a year of recycled, energy-efficient, and other green products - count as a "green job"? What about the loading dock laborer whose job it is to make sure all packaging materials are recycled? Or the facility manager working to replace maintenance staples with green cleaning products? Are these counted among the "green jobs"? Possibly, but I doubt it.

Fact is, there's no good definition of "green job." Consider this report, released last week, by Raquel Rivera Pinderhughes, professor of urban studies at San Francisco State University. Titled Green Collar Jobs: An Analysis of the Capacity of Green Businesses to Provide High Quality Jobs for Men and Women with Barriers to Employment (Download - pdf), it focuses on opportunities in the San Francisco Bay Area. According to Pinderhughes,

Green collar jobs are blue collar jobs in green businesses - that is, manual labor jobs in businesses whose products and services directly improve environmental quality...What unites these jobs is that all of them are associated with manual labor work that directly improves environmental quality.

Pinderhughes lists 22 types of green collar jobs, from food production (using organic and/or sustainably grown agricultural products) to furniture making (from environmentally certified and recycled wood), from parks and open space (maintenance and expansion) to printing (with non-toxic inks and dyes and recycled papers). It's a good list, but it doesn't seem to cover all that's out there.

Another report, Green-Collar Jobs in America's Cities (download - pdf), released for the Pittsburgh event, lays out steps for creating comprehensive green-collar job strategies at the local level. It also profiles some of the great work already underway around the country. The guide - published by Green For All, the Apollo Alliance, the Center for American Progress, and the Center on Wisconsin Strategy - focuses on local green jobs in clean energy industries: energy efficiency, renewable energy, alternative transportation, and low-carbon fuels.

Yet another new report, Greener Pathways, from the same consortium, profiles some of the best examples in the U.S. where work is underway to develop green jobs, including green construction career development in California, Iowa's biofuels job-training bonds, wind technician training in Oregon; and Pennsylvania's green re-industrialization.

It's all very encouraging, but it feels like there's one key group that's not yet at the table: companies. A look at the impressive speaker roster for the Pittsburgh event reveals only eight of 86 speakers from the private sector - and only three large companies: BP, Gamesa, and Johnson Controls.

Why aren't bigger companies more engaged? Do they not foresee a need for talent in this arena? Are their labor pools overflowing? Or are they simply not tuned in to the opportunity? Any ideas?

For now, groups like the Apollo Alliance and Green for All will have to go it alone, and they have their work cut out for them, helping to ensure, in the words of Green for All founder and president, Van Jones, that "the clean-tech wave lifts all boats." It won't be easy, especially without the active participation of companies in the clean and green sector.

As Jones told me recently: "The next set of challenges have to do with going from rhetoric to reality."