More than 170 countries agreed early Saturday morning to limit emissions of key climate change-causing pollutants found in air conditioners, a significant step in the international effort to keep global warming from reaching catastrophic levels. The deal reached in Kigali, Rwanda, comes after years of wrangling over HFCs—short for hydrofluorocarbons—and could on its own prevent a 0.5°C (0.9°F) rise in temperature by 2100.