Canada, Mexico, and the U.S. are formally proposing to curb production and use of a family of potent greenhouse gases under the Montreal protocol, a treaty to safeguard Earth’s protective stratospheric ozone layer. The three countries want the world to ratchet down releases of hydrofluorocarbons, which are refrigerant chemicals that have largely replaced ozone-depleting substances such as chlorofluorocarbons. On an equal-mass basis, HFCs, used in refrigerators and car air conditioners, have the potential to warm the atmosphere tens to thousands of times more than carbon dioxide. Global atmospheric concentrations of these synthetic chemicals are increasing. The three North American countries are proposing an amendment to the Montreal protocol that would extend the treaty to cover HFCs. “Without this proposal, HFC use in developing countries is anticipated to grow substantially,” because of growing demand for refrigeration and air conditioning, according to EPA. The proposal will be discussed by the 196 countries that are partners in the Montreal protocol at meetings in June and November. More information on the plan is available at www.epa.gov/ozone/intpol/mpagreement.html.