Reuters: The United States intends to work toward reducing emissions of potent greenhouse gases found in refrigerators and air conditioning systems but has not yet decided which international venue to use to advance the issue, U.S. officials said on Monday. In a letter to a U.N. agency, the U.S. State Department said hydrofluorocarbons, known as HFCs, “pose a very significant further threat to the climate system because of their high global warming potentials.” The letter, by Deputy …