Emissions of CFC-11, a chlorofluorocarbon once frequently used in cooling and insulation systems to improve the quality of life, can also endanger life. Upon entry into the stratosphere where solar ultraviolet radiation is strong, CFC-11 decomposes, resulting in the release of chlorine, which degrades the ozone layer that shields life from harmful UV rays. In 2018, a team of scientists discovered an alarming upward spike in global CFC-11 emissions from 2013 to 2017. In 2019, a second team traced much of this spike to eastern China. Then in 2021, both teams found that global CFC-11 emissions had spiked downward from 2018 to 2019, and traced much of this downward spike to the same area—indicating that China had most likely curbed illegal manufacture of the ozone-depleting chemical. As a result, a major impediment to the ozone layer’s full recovery was now removed.

Key to the successful tracking and tracing of CFC-11 emissions from China was the Advanced Global Atmospheric Gases Experiment (AGAGE). Measuring the ozone-depleting and greenhouse gas composition of the Earth’s atmosphere continuously for the past 45 years through a global network of sophisticated monitoring stations, AGAGE has contributed significantly to the protection of life on Earth. In addition to monitoring and pinpointing sources of emissions of chemicals banned by international agreements such as the Montreal Protocol, which outlawed the use of chlorofluorocarbons (CFCs) such as CFC-11, the network has estimated the lifetimes of ozone-depleting and greenhouse gases in the atmosphere; determined concentrations of the atmosphere’s major “cleansing agent,” the hydroxyl radical (OH); and provided data to inform international policy discussions concerning atmospheric greenhouse gas emissions that drive climate change.

To celebrate these and other achievements, and to explore the network’s history and impact, recent results and next steps, more than 70 AGAGE scientists, collaborators and invited guests from research institutions around the world—many representing dozens more researchers at their home institutions—gathered on October 8-13 at the MIT Endicott House and online to attend a conference celebrating the 45th anniversary of AGAGE ((formerly known as the Global Atmospheric Gases Experiment (GAGE) and Atmospheric Lifetime Experiment (ALE)). (See 45th anniversary photo gallery.)