Warnings from the chemical sector on the outlook for earnings are piling up — just as worrying signs about global demand and economic growth begin to multiply across the board. June has proved a bad month for chemical producers, with four European companies warning about their profit outlook for the rest of the year. This week, Lanxess joined Croda, K+S and Victrex in preparing investors for the impact of weak demand, tougher pricing, or destocking by customers. In the US, Cabot blamed softer global demand as it ditched its full-year…