Across New York City, for example, the police arrested black people on low-level marijuana charges at eight times the rate of whites over the last three years, with Latino people arrested at five times the rate of whites. The race effect was especially clear in Brooklyn, where officers arrested people for marijuana possession in the Canarsie precinct, which is 85 percent black, at four times the rate of the precinct that includes Greenpoint, where only 4 percent of the residents are black, despite the communities producing marijuana complaints by telephone at the same rate.

A similar picture emerged in Queens, where the police precinct covering majority-black Queens Village had an arrest rate more than 10 times that of the precinct that serves Forest Hills, where blacks are a tiny portion of the population, even though the rate of complaints was the same.

These disparities are all the more indefensible because low-level marijuana arrests have no public safety benefit. A 2017 analysis by Harry Levine, a sociology professor at Queens College, debunked the oft-heard claim that petty marijuana arrests get serious offenders off the street, noting that 76 percent of those arrested for marijuana possession during the previous year had never been convicted of any crime.

But such arrests do immense damage to people who often have had no other contact with the criminal justice system. The charges are typically dismissed if the person stays out of trouble for a year, but over that period, having an open court record can get the person shut out of housing, job opportunities or entry into the armed services. In addition, people who journey to court to answer charges that the system intends to dismiss end up losing hundreds of dollars in wages.

Beyond that, the arrest disparities are strongly reminiscent of the ones that persuaded a Federal District Court judge to rule in 2013 that the city’s stop-and-frisk practice violated the Constitution by illegally detaining and frisking minority citizens over a period of many years. If the city isn’t careful, it could find itself hauled into court again — this time for marijuana arrests.