Reuters: California aims to avoid major economic shocks with its carbon cap-and-trade system slated to start in 2012, the state’s chief climate change regulator said on Monday, adding that the most populous U.S. state would try to harmonize its system with any federal plan. California vaulted to the vanguard of U.S. climate change in 2006 with an aggressive law that aimed to cut greenhouse gas emissions to 1990 levels by 2020 and make it the trend-setter in clean energy and …