OAKLAND, Calif. — Building a green economy has the potential to affect millions of workers in occupations throughout the country, and a new report highlights some of those jobs than can be transformed, with the right investment, into green jobs.

The Job Opportunities for the Green Economy report looks at six investments areas, then shows at the current states of jobs in each area. In total the report shows how 45 occupations employing more than 14 million people across the country can be boosted through investments in green measures.

The report is not an exhaustive list of all green investments or green jobs, but is meant to give a snapshot of a few possible green jobs, said one of the authors, Robert Pollin, Department of Economics and Political Economy Research Institute, University of Massachusetts-Amherst.

"We all know that we have to build a green economy. This is a necessity," he said in a press briefing. "We just show the number of people who are now engaged in these activities that are going to be very important in building the green economy."

The report looks at the investment areas of building retrofits, mass transit, energy-efficient automobiles, wind power, solar power and cellulosic biofuels. For the most part, the jobs identified are common, pre-existing categories.

"The jobs are real, the jobs are there," said Marco Trbovich, assistant to the president of the United Steelworkers of America. Investment in these areas, he said, will create job growth as well as job retention. He cautioned, though, that in many cases public policy will need to change to spur the green economy. For instance, a long-term production tax credit for renewable energy would ensure more investment in wind and solar than one-year tax breaks that might not be renewed, he said.

"Solving global warming is a matter of investment," said Bracken Hendricks, senior fellow at the Center for American Progress. "As we work to reverse the dangerous cost of global warming, we will be investing in very, very concrete job creation and infrastructure."

Although the report does not provide specifics on how the jobs could be affected by investment, the general expectation is that all the occupations could see job growth and wage increases. The report also does not look at service jobs such as accountants, lawyers, clerks and human resources workers. As some job categories grow, though, related service jobs are expected receive more demand.

"Green jobs will not just be in one part of one new niche of the economy," said Carl Pope, Sierra Club executive director. "These are not niche jobs, these are mainstream jobs."

Van Jones, the founder and president of Green For All, said an expanding green economy will provide a chance to fight pollution as well as poverty by providing work for the unemployed or people with jobs that don't pay living wages.

"We want to make sure that this green wave that is going to be created is a green wave that can lift all boats," he said. "As we move forward in this clean and green economy, we have an opportunity to make sure it is inclusive from the beginning."

The report looks at how many people are employed in each job category and the average wages in 12 states: Florida, Indiana, Minnesota, Missouri, Nebraska, New York, Ohio, Oregon, Pennsylvania, Tennessee, Virginia, and Wisconsin.

For the most part, the green jobs aren't anything new and include a range of occupations. To retrofit buildings, electricians, carpenters and building inspectors will be needed. Expanded mass transit will require civil engineers as well as bus drivers. Car companies that make energy-efficient vehicles will need to enlist computer software engineers, welders and engine assemblers. And the creation of wind turbines will rely heavily on steelworkers.

The report was authored by Robert Pollin and Jeanette Wicks-Lim of the Department of Economics and Political Economy Research Institute of the University of Massachusetts-Amherst and commissioned by the Natural Resources Defense Council. It is being released in cooperation with the Green Jobs for America Campaign.