Overview
- The analysis published in PNAS by an MIT team led by Susan Solomon and Jian Guan, released Tuesday, June 30, 2026, reconstructs 20th‑century atmospheric chemistry to reattribute an early phase of ozone loss to tetrachloromethane (CCl4).
- Researchers combined atmospheric models, historical chemical production records and ice‑core measurements to estimate past emissions and the stratospheric ozone response that points to CCl4 as the dominant human driver from about 1920 to 1960.
- The study confirms that CFCs became the much larger driver of ozone depletion after mid‑century, matching laboratory findings from the 1970s and satellite observations of the 1980s that identified severe Antarctic losses.
- Authors say the CCl4‑driven thinning was substantially smaller than later CFC damage and was too limited to produce detectable public‑health effects, though it shows earlier industrial chemicals did alter the atmosphere.
- Because both CCl4 and CFCs were restricted under the 1987 Montreal Protocol, the finding changes historical attribution but not policy or the outlook that international controls have put the ozone layer on a recovery path toward mid‑21st century.