Nations worldwide will begin limiting the amount of hydrofluorocarbons (HFCs) they use within the next dozen years, under an international deal finalized earlier this month. HFCs, potent greenhouse gases used as refrigerants, were adopted as replacements for ozone-depleting chemicals including chlorofluorocarbons. Under an agreement completed in Kigali, Rwanda, industrialized countries will begin reducing their use of HFCs by 2019. Most developing countries, including China, will freeze their HFC use starting in 2024 then pare their consumption back starting in 2029. A handful of developing countries that have hot climates—Persian Gulf states, India, and Pakistan—opted for a slower HFC reduction path. They agreed to freeze use of these substances starting in 2028 and begin ratcheting it back by 2032. Global chemical companies, which are introducing more climate-friendly alternatives to HFCs, such as hydrofluoroolefins, support the deal. But Greenpeace International’s Paula Tejón Carbajal says the success of the agreement will hinge on how fast developing countries switch to so-called natural refrigerants, such as ammonia or carbon dioxide, and avoid the use of HFOs, which she calls toxic.