The achievement is roughly equal to taking 12 million cars off the road or saving 6 billion gallons of gasoline a year.
"California set the toughest emissions targets in the nation, tracked progress and delivered results," California Gov. Jerry Brown said. "The next step is for California to cut emissions below 1990 levels by 2030 - a heroic and very ambitious goal."
California is ahead of schedule in relation to Assembly Bill 32 passed in 2006, which mandated that the state reduce its emissions to 1990 levels (431 million metric tons) by 2020.
Former governor Arnold Schwarzenegger applauded the news on Twitter.
California emitted 429 million metric tons of climate pollutants in 2016, a drop of 12 million metric tons, or 3 percent, from 2015, according to the Greenhouse Gas Emissions Inventory.