Reuters: The Obama administration wants to ensure that legislation being crafted by Congress to fight global climate change does not violate international trade rules and backfire on U.S. exports, the top U.S. trade official said in a letter to a Republican lawmaker. The letter from U.S. Trade Representative Ron Kirk, released late on Tuesday, was in response to questions Rep. Joe Barton raised about Energy Secretary Stephen Chu’s recent suggestion that the United States may need to impose a …