Reuters: A new U.S. commitment to tackle global warming as outlined by President Barack Obama will be the focus of attention on Wednesday at a meeting of international environment ministers. Obama has already pledged to cut U.S. greenhouse gas emissions to 1990 levels by 2020, and observers will be looking to see if U.S. delegates give new details of American plans for action. The three-day summit brings together industrialized and developing countries on the Italian island of Sicily. …