California cut greenhouse gases by 2.7 percent in 2016, marking a return to pre-1990 levels.

A 2006 mandate signed into law by former Governor Arnold Schwarzenegger required that the state reduce emissions to 431 million metric tons of carbon – the level produced in 1990 – by 2020. The 429.4 million metric tons produced in 2016 satisfied the mandate four years early.

According to data released last week by California’s Air Resources Board, the emissions reduction was spurred by a drastic reduction in electric power emissions, which fell from 83.67 to 68.58 million metric tons in 2016. The reduction is due to California’s aggressive investment in renewable energy. According to the air board, solar generation grew 33 percent in 2016, while rainy weather boosted hydropower by 39 percent. Use of natural gas for electric generation likewise fell 15 percent that year.

The overall drop in emissions was also aided by regulating vehicle emissions and a carbon pricing and trading program shared with Quebec, Canada.

The data also indicated emissions reductions in the industrial category – including oil and gas production and general fuel use – and agriculture. By contrast, emissions from commercial and residential sources and transportation increased between 2015 and 2016.

“California set the toughest emissions targets in the nation, tracked progress and delivered results,” Governor Jerry Brown said in a July 11 tweet. “The next step is for California to cut emissions below 1990 levels by 2030 — a heroic and very ambitious goal.”

Brown is referring to a state law mandating that emissions levels drop 40 percent below 1990 levels by 2030. The governor also issued an executive order requiring emissions to drop 80 percent below 1990 levels by 2050.