Reuters: The United States, Canada and Mexico have proposed using an existing international protocol to reduce emissions of potent greenhouse gases called hydrofluorocarbons (HFCs) used in refrigerators and air conditioners, the State Department said on Tuesday. The State Department said the three countries believed the Montreal Protocol, which regulates hydrochlorofluorocarbons (HCFCs) blamed for depleting the ozone layer, could also help phase down hydrofluorocarbons (HFCs) used in cooling …