A decade after California took a global lead by adopting its comprehensive policy to clear the air, transition to clean energy and reduce climate pollution, here’s what we know about what its effect has been: The economy has grown, in recent years outpacing the rest of the nation. Fueled by billions of dollars in private investment, a thriving clean-energy sector has blossomed, creating hundreds of thousands of jobs. Greenhouse gas emissions have dropped, and are on pace to meet the target of rolling them back to 1990 levels by 2020.