The latest auction in California's cap-and-trade market for greenhouse gases fell sharply below expectations, as buyers purchased just 2% of the carbon credits whose sale funds a variety of state programs -- notably, the proposed high-speed rail project. The quarterly auction, conducted May 18 and announced Wednesday, will provide just $10 million for state programs, including $2.5 million for the bullet train. The rail authority had been expecting about $150 million. Whatever prompted the lack of buyers, the auction is a stark example of the uncertainty and risk of relying on actively-traded carbon credits to build the bullet train. The...