Money can grow on trees.

So proclaims the National Organization for the Reform of Marijuana Laws (NORML) in a new Times Square billboard that urges lawmakers to tax and regulate marijuana like alcohol.

Legalizing marijuana will raise billions of dollars in new tax revenue, the ad declares. How many billions?

According to a 2005 Harvard University analysis endorsed by over 500 distinguished economists, replacing marijuana prohibition with a system of taxation and regulation would produce savings and tax revenues of between $10 billion and $14 billion per year.

A separate economic review, conducted by George Mason University professor Jon Gettman in 2007, estimates that the total amount of tax revenue that could be derived from the present marijuana market would be far higher.

He calculates that the diversion of this market from the taxable economy deprives state and national budgets of $31.1 billion annually.

For state and local governments, taxing and regulating pot could reduce growing deficits. For instance, last summer Oakland, California voters overwhelmingly approved a ballot measure to raise the business tax paid by city-licensed medical marijuana dispensary operators. It is estimated this effort will raise up to a couple of million dollars annually.

In January, members of the California Assembly, Committee on Public Safety, similarly gave a green light to legislation to regulate the commercial production and retail sale of marijuana statewide. Such a plan, if enacted, would raise some $1.4 billion per year for California’s cash-strapped coffers.

But such savings and revenues aren’t only limited to marijuana hotbeds like California. Most recently, Rhode Island state officials reported that decriminalizing minor marijuana possession offenses—a policy whereby police issue offenders tickets rather than making a criminal arrest—could save taxpayers over $230,000 per year. Legalizing and regulating the adult use of the drug outright would conceivably raise millions more.

Presumably, critics of marijuana law reform will allege that legalization will yield few, if any, substantial cost savings to taxpayers. They argue that both alcohol and cigarettes are taxed; yet they maintain that there overall costs to society ultimately outweigh their revenue.

Ultimately, however, even if legalization¹s cost savings were minimal, regulating Ame­rica¹s top cash crop would still be the right thing to do because it would take the pot production out of the hands of criminal enterprises and, increasingly, violent drug gangs.

Any way you do the math, America can no longer afford marijuana prohibition.

It is time to replace this bankrupt policy with legalization, regulation, and education.