I'm a terrible eco-Marxist conspirator. I had to look it up. Thus Wikipedia:
A green job, also called a green-collar job is, according to the United Nations Environment Program, "work in agricultural, manufacturing, research and development (R&D), administrative, and service activities that contribute(s) substantially to preserving or restoring environmental quality. Specifically, but not exclusively, this includes jobs that help to protect ecosystems and biodiversity; reduce energy, materials, and water consumption through high efficiency strategies; de-carbonize the economy; and minimize or altogether avoid generation of all forms of waste and pollution."
But there are a few caveats that should be borne in mind. This is essentially one-time stimulus -- we should not think, and we should not hope that a green infrastructure will be a permanent engine of job creation -- that would mean that it required more people to maintain than the old infrastructure, and would be proportionally more expensive as a result.
We could permanently create manufacturing jobs if the industries that grow up around converting our own economy are successful enough to generate exports. That's possible. But I wouldn't want to promise that to people. There's always heavy competition in the export market. Our manufacturing sector in the United States is in a long-term decline. Perhaps we will end up with thriving new export industries. But it's entirely possible that, as with solar PV and wind, the manufacturing advantages of a country like China will leave our industries on the defensive.
Just as "green jobs" are not going to permanently lower our unemployment rate, they are not going to spring up overnight, either. Unemployment in the United States has a lot to do with the fact that a third of our kids do not graduate from high school. Millions of people are in prison, millions of people are on parole. And you can't pick up a gaggle of high school dropouts from Home Depot, stop off at the prison for the day's parolees, and go and build a wind farm. You have to train people.
There are people to be trained, no doubt. But then you have to decide how fast we're going to convert the economy. If you convert the economy in five years, you'd create a lot of jobs, but in five years you'd have millions of people whose work was finished and whose skills are next to useless. On the other hand, you could do it in fifty years, and then you would be training people for a life-long career. But this would only create one-tenth as many jobs as the first option, and we wouldn't realize the benefits of the conversion for half a lifetime. Downsides either way.
None of this is unique to "green jobs" -- these problems are ubiquitous whenever the government tries to create jobs. Rarely do government programs hit the "sweet spot" of long- or even medium-term job creation. People want "shovel ready" projects. People like "job training," but this is rarely linked to the projects for which we need workers. You could, and it'd be a good and practical thing to do, train a million workers to do residential and commercial weatherization and then weatherize every significant permanent structure in the United States over the next twenty years. Those would be green jobs. But people would be apoplectic at the sticker price.