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.