California’s insurance commissioner on Monday asked all insurance companies doing business in the state to voluntarily divest from coal companies and said he will also require insurance companies to disclose their coal company holdings. Coal use by utility companies has plummeted amid low natural gas prices and new federal regulations aimed at curbing carbon emissions, a major contributor to climate change. Ten years ago coal produced 50 percent of the nation’s power supply but now accounts for only about 35 percent, according to the U.S. Energy and Information Administration.