San Francisco Chronicle: Some cities urge residents to go on citywide exercise kicks. Others promote municipal book clubs. Berkeley wants its citizens to go on a collective low-carbon diet. To meet its ambitious goals to reduce greenhouse gas emissions, Berkeley is encouraging all 100,000 residents to join support groups to help individuals fight global warming. Like Alcoholics Anonymous and Weight Watchers, the groups are part social, part confessional and partly about accountability. “It does …