In a decision that could have broad reach, Colorado’s second-highest court on Thursday retroactively threw out a woman’s 2011 convictions for marijuana offenses that are now legal.

The woman, Brandi Jessica Russell, was appealing her convictions for possessing less than an ounce of marijuana and possessing marijuana concentrate, among other charges, when Colorado voters passed Amendment 64 in 2012. The measure made possession of up to an ounce of any kind of marijuana legal for anyone in the state age 21 and over.

“Amendment 64, by decriminalizing the personal use or possession of one ounce or less of marijuana, meets the statutory requirement for ‘a significant change in the law’ and eliminates and thus mitigates the penalties for persons convicted of engaging in such conduct,” a three-judge panel of the Colorado Court of Appeals wrote in the opinion.

The court said its decision applies only to people who were in the midst of an appeal on the effective date of Amendment 64, which was on Dec. 10, 2012.

Russell’s attorney, Brian Emeson, praised the decision, saying it provides at least some people a way to remove a black mark on their records for things Colorado voters now say shouldn’t be punished.

“It’s a decision that certainly represents the will of the citizens of this state,” he said.

Colorado Attorney General John Suthers said in a statement he disagrees with the appeals court’s conclusion that Amendment 64 can be applied retroactively. He said he would likely appeal to the Colorado Supreme Court.

The Supreme Court already has one other weighty marijuana-related issue on its plate, after agreeing in January to take up the case of a man fired from his job for testing positive for marijuana, even though he is a legal medical marijuana patient under state law.

Thursday’s ruling can now be cited as precedent by others appealing their convictions, but marijuana advocate Brian Vicente said it is unknown how many people could be eligible for significant relief. Possession of less than an ounce of marijuana was previously a petty offense in Colorado, and state law specifies that conviction for the offense “shall be punished by a fine of not more than one hundred dollars.”

Vicente said the ruling may be more significant for people convicted of possession small amounts of marijuana concentrate — which was a felony when Russell was convicted and is now treated as a level-1 drug misdemeanor if people are convicted of possessing more than an ounce but fewer than three ounces.

The appeals court’s ruling notes that, “Marijuana and marijuana concentrate are treated separately under the Colorado Criminal Code … but are deemed the same under Amendment 64.” For that reason, the appeals court determined that Russell’s conviction for marijuana concentrate — which brought a sentence of four years of supervised probation — should also be tossed.

Vicente said the same logic could apply to adults convicted of growing six or fewer marijuana plants, which was also a level-1 drug misdemeanor prior to Amendment 64.

Suthers, however, said it is unlikely the ruling will lead to anyone being released from prison.

“It is highly unlikely that there is anyone incarcerated at this time strictly for possession of marijuana concentrate of less than one ounce,” he said in a statement.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold