San Diego County released a draft climate plan on Thursday, pledging to dramatically reduce greenhouse-gas emission by limiting backcountry sprawl and using at least 90 percent renewable energy by 2030. The proposed blueprint for fighting global warming comes five years after the San Diego chapter of the Sierra Club first sued the county over an earlier version of the plan. Lawyers for the environment group argued in court that the county’s original vision lacked specificity on how it would realize deep cuts in climate-warming emissions.