Sacramento Bee: Lower pollution levels brought on by California’s struggling economy have prompted the state to ratchet down its proposed cap on greenhouse gas emissions for 2012. On Friday, the California Air Resources Board unveiled new regulations for its cap-and-trade program, which places limits on the amount of carbon that the state’s largest oil refineries and power companies can emit. Under the new rules, ARB will cap the amount of carbon emissions by those companies at 168 million metric tons for…