Over the weekend, nearly 200 countries signed an amendment to the 1987 Montreal Protocol. The new deal created a legally binding commitment to limit hydrofluorocarbons (HFCs) – a harmful gas often released during the creation and improper disposal of air conditioners and refrigerators. HFCs are a man-made colorless, odorless, and unreactive gas that became a popular substitution for chlorofluorocarbons (CFCs), the gas originally targeted by the Montreal Protocol due to its disastrous effect on the ozone layer. Now that CFCs are almost gone, HFCs are on the rise, but instead of destroying the ozone like its predecessor, HFCs have the capability to trap heat with a global warming potential of 100-3000 times that of carbon dioxide. Their stable chemical composition also allows some HFCs to remain in the atmosphere for hundreds of years. This weekend’s new amendment seeks to phase out HFCs in a three-tiered system with rich countries starting in 2019, China and other ambitious countries in 2024, and all other developing countries in 2028. If the agreement reaches the same success that it had with CFCs, it has the potential to curb approximately .5 degrees Celsius of future warming – a significant amount compared to the Paris agreement’s goal to limit heating “well below” 2 degrees Celsius.