Skyrocketing incarceration rates for nonviolent drug offenders have come to symbolize the futility of the national "war on drugs." Even the most ardent drug legalization opponents are beginning to view drug use through the lens of public health, rather than criminal justice.

This shift in focus is evident at the White House's Office of National Drug Control Policy, which for decades has been the command center of the federal war on drugs. The ONDCP now emphasizes "balance" as a key component of federal drug strategy. "Drug addiction is not a moral failing but rather a disease of the brain that can be prevented and treated," the agency states on its website. "Drug policy is a public health issue, not just a criminal justice issue."

That said, it doesn't seem that the nation's law enforcement agencies have embraced the new approach. While the number of arrests for all offenses has declined nationally since 1991, the share of arrests related to simple marijuana possession has more than tripled over the same time period.

In absolute terms the number of marijuana possession arrests has more than doubled since 1991, although it has subsided slightly in recent years. But the percent of all arrests related to marijuana possession has steadily risen even as public attitudes toward the drug have shifted, states have relaxed their marijuana laws, and new research has come to light thoroughly debunking the Reefer Madness mindset of earlier decades.

At least 658,000 people were arrested for marijuana possession in 2012, accounting for 42 percent of all drug arrests and 5.4 percent of all arrests for any offense, according to FBI data. The actual numbers are likely even higher, since a handful of states either don't report arrest data to the FBI, or only do so on a limited basis.

But the focus on marijuana arrests varies considerably by state. In New York, an astonishing one out of every eight arrests - 12.7 percent - are for simple marijuana possession. But across the state line in Massachusetts, fewer than one out of every 100 arrests are for marijuana possession.

Marijuana possession arrests by state, 2012

Both states decriminalized marijuana possession - New York in 1977, and Massachusetts in 2009. But in New York, a loophole in the decriminalization law allows arrests for marijuana that is in possession "in public view." If a police officer can trick an unsuspecting person into emptying their pockets - say, during a "stop and frisk" - any marijuana in those pockets is now in public view. Out come the cuffs.

The overall picture is similar if you look at the number of marijuana arrests per 1,000 marijuana users in a given state. Those figures show that Nebraska and Louisiana are the riskiest states to smoke marijuana in, with roughly 50 arrests per 1,000 users. In contrast, a marijuana user is about 40 times less likely to get arrested in Massachusetts, where there are 1.3 possession arrests per 1,000 users.

The state-level data underscore the inconsistency of prohibitionist marijuana policy. New York devotes considerable man-hours and dollars to marijuana possession enforcement compared to Massachusetts, but usage rates are roughly the same in both states: 8.2 percent of New Yorkers admitted using marijuana in the past month, compared to 9.4 percent of Massachusetts residents. So what return, exactly, is New York seeing on its investment in marijuana policing?

The costs of this kind of overzealous drug policing are considerable. The ACLU estimates that in 2010, states spent a total of $3.6 billion on marijuana possession enforcement. But the costs born by the people arrested are even greater. FBI's crime data doesn't track whether arrests lead to convictions, but an arrest in an of itself can be a huge burden, financial or otherwise.

It may cost thousands of dollars in legal fees to fight a marijuana arrest. Some offenders are given the option of attending a drug treatment program  in exchange for leniency. But rehab makes little sense for a recreational marijuana user, and these programs can also be prohibitively expensive. Moreover the arrest itself, regardless of conviction, can show up in background checks for job applications.

Fortunately, the trend toward full legalization appears to be a durable one, at least judging by the public opinion numbers. As more states move toward legalization, law enforcement agencies will be able to allocate that $3.6 billion elsewhere. A good place to start might be the 53 percent of violent crimes that went unsolved in 2012.