Rewind four years ago to the presidential campaign and you'll recall that An Inconvenient Truth, a documentary about climate change, was fresh in the minds of many Democrats.  

As a candidate Barack Obama pledged to enact a market-based cap-and-trade carbon-emissions system designed to reduce air pollution. Obama envisioned the government auctioning off carbon-emission permits for a set price per metric ton of a greenhouse gas such as carbon dioxide.

Under Obama's plan, auctioning revenue would hand the president an extra $15 billion per year, which he would invest in clean-energy technology and -- voila! Five million new jobs in the clean-energy sector in the next 10 years.

We're reviewing that 5-million figure here.

Despite the president's support for cap and trade, the bill stalled in Congress. That means the main pot of money intended to create Obama's 5 million green jobs -- $150 billion over 10 years -- doesn't exist.

Obama would have another problem in meeting his original green jobs promise -- it would be difficult to prove he achieved it.

That's because the federal government didn't count green jobs until this year. But two years ago, Congress appropriated money for the Bureau of Labor Statistics to survey businesses and establish a baseline number. The bureau says the U.S. had an estimated 3.1 million jobs related to green goods and services in 2010. Later this year we'll learn how many green jobs existed in 2011. But we do not know how many comparable green jobs existed in 2009 or in the pre-Obama years.

Economists from the Brookings Institution, a nonpartisan policy research group, made their own definition of a green job and calculated seven years' worth of historical data from 2003 to 2010. They estimate the U.S. economy had 2.1 million green jobs in 2003 and 2.7 million in 2010.

"Green job growth has increased during the Obama Administration, and green jobs have grown faster than jobs in all sectors,” said Jonathan Rothwell, one of the Brookings researchers who wrote the report.

But Rothwell cautioned against assuming those new jobs were the result of Obama policies. He noted that few of the jobs added -- about 17 percent of the roughly 211,000 new jobs in 2009 and 2010, were in the clean-technology areas targeted by the Obama administration.

The American Recovery and Reinvestment Act, better known as the economic stimulus, supported green industries through more than $90 billion in tax credits, grants, loans and loan guarantees for bolstering public transit and increasing clean energy production in the wind, solar, geothermal, biofuel, and electric-car industries.

"The stimulus bill and Obama administration budgets have certainly increased spending on green activities, and that spending has created jobs,” Rothwell said. "Whether or not Obama administration policies have been effective or worthwhile investments of tax dollars very much depends on the program, how it was designed and implemented, and how the companies fare going forward.”

Kate Gordon, a senior fellow at the liberal policy research group, the Center for American Progress, said the Obama administration has supported green job growth in more ways than direct spending. Case in point: His administration set higher fuel economy standards, which encourage the production of fuel-efficient vehicles and vehicles running on alternative energy sources.

The last point we should address is the timeline. It is true that Obama's promise came with a 10-year deadline. Theoretically, he could win reelection, find a source of revenue to fund green job growth and still meet that goal. Nonetheless, the key to his green-job creation plan -- a cap-and-trade law -- has no prospects of passing in 2012. Even if he wins reelection, he is likely to face ongoing opposition by Republicans in Congress, making a landmark law on climate change improbable.

The near future looks bleak for Obama's green jobs promise, but since he gave himself a 10-year window, we'll leave this promise In the Works for now.