It may prove to be one of the most important milestones in the history of humankind: representatives from nearly 200 member countries of the Montreal Protocol have agreed on a deal to cut greenhouse gas emissions during a summit in Kigali, Rwanda. The deal would reduce hydrofluorocarbons (HFCs), which is the fastest-growing greenhouse gas on the planet, and it comes at a time where scientists are warning that climate change is quickly spiraling out of mankind’s control.

HFCs are usually used in refrigeration and air conditioning — ironically, as a “green” measure instead of substances that were blamed for depleting our ozone layer. A cut in HFCs could prevent up to 0.5 degrees Celsius (0.9 degrees Fahrenheit) of global warming by the end of this century, according to a statement from the United Nations. That won’t be enough, but it’s a very important start.

“It is not often you get a chance to have a 0.5-degree centigrade reduction by taking one single step together as countries — each doing different things perhaps at different times, but getting the job done,” said U.S. Secretary of State Kerry in a speech Friday, as quoted by CNN.

“Last year in Paris, we promised to keep the world safe from the worst effects of climate change. Today, we are following through on that promise,” said UN Environment chief Erik Solheim. “This is about much more than the ozone layer and HFCs. It is a clear statement by all world leaders that the green transformation started in Paris is irreversible and unstoppable. It shows the best investments are those in clean, efficient technologies.”