Last year was a good one for the global chemistry enterprise. Business expanded in most regions, especially in the U.S., where chemical output increased a robust 3.8%. The 2016 forecast is for continued growth, thanks to low energy prices and healthy customers in industries such as pharmaceuticals and auto manufacturing. Yet executives see clouds in China’s slowing economy, turmoil in Brazil, and weakness in Europe. The economic winds are favorable for now, but they may not last.