Tom Johnson, the coordinator of the West Central MEG Drug Task Force, gathers marijuana plants after a drug raid. He doesn't realize that he's part of the problem. (AP Photo/La Crosse Tribune, Erik Daily)

New arrest data from the FBI shows that arrests for simple marijuana possession are down year-over-year, from 658,000 in 2012 to 609,000 in 2013. They are down sharply from their peak of 775,000 in 2007. But marijuana possession arrests still make up about 5.4 percent of all arrests, and they account for a whopping 41 percent of all drug arrests.

The total number of arrests for all offenses continues to drop sharply, from a high of 15.3 million in 1997 to 11.3 million in 2013. But marijuana possession arrests have not declined at the same rate - these arrests accounted for 1.6 percent of all arrests in 1990, but make up 5.4 percent of all arrests today.

There's a bit of a caveat here - the FBI data doesn't distinguish between full-on arrests for marijuana possession, and citations for the same in the 18 or so states that have decriminalized possession. But depending on the state, even a citation can have long-lasting consequences.

Moreover, arrests for all drug offenses made up a record share - 13.3 percent - of total arrests this year. Drug violations represent the single largest category of arrests tracked by the FBI.

As NORML notes, if we assume ACLU's conservative estimate of a cost of $750 for each marijuana possession arrest, it means that states spent more than $450 million on these arrests in 2013 alone.

These numbers come from FBI tallies of state and local police department arrest reports. Because participation in the program is voluntary and some states don't participate in it at all, these figures are a floor - not a ceiling.

With four states plus D.C. having legalized marijuana since 2012, the cognitive dissonance underlying our nation's drug policies is becoming more stark. Certain states are spending millions of dollars annually to arrest and incarcerate people for a behavior that may be completely legal just across the border.

That may help explain why calls for full federal decriminalization and legalization of marijuana have grown louder this year. According to ACLU's estimate, in 2010 the states spent a total of $3.6 billion on marijuana possession enforcement, from arrests to court costs to incarceration.

As I noted earlier back in August, state-level discrepancies in marijuana enforcement, even between states with ostensibly similar regulation regimes, can be striking. 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

However, New York's marijuana arrest numbers are set for a big drop. The New York Times reports that the NYPD will stop arresting people for pot possession and instead simply issue them a ticket - putting the department in compliance with the state's decriminalization law that was passed nearly 40 years ago.

Overall, the decriminalization of marijuana is notable for the unity of public opinion behind it and the resistance of most legislators to even talk about it.. According to the Pew Research Center, 76 percent of Americans say people caught with small amounts of marijuana should not be subject to jail time. Even groups that fiercely oppose the full legalization of marijuana, like Project SAM, agree that possession of small amounts should be a civil offense, not a criminal one.

But most of our national-level lawmakers cut their teeth during the "tough on crime" days of the '80s and early '90s. Legislative change, particularly at the federal level, will be slow in coming. Which is why voters in many states have simply taken the issue in their own hands and passed drug reform measures via ballot.