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Disaster averted: Guiding the recovery of the ozone layer with atmospheric monitoring and analytical chemistry

Dr. Steve Montzka,
National Oceanic and Atmospheric Administration, Boulder, Colorado.

International agreements arise out of a common goal to resolve or prevent an adverse condition. In the case of ozone-layer depletion, a prime example is the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. In 2003, Kofi Annan hailed this Protocol as being “perhaps the single most successful international agreement to date,” as it brought together policymakers, industry and scientists with the goal of reducing the threat to the ozone layer posed by human-produced ozone-depleting substances.

As with any agreement, however, success is more likely when commitments can be independently verified and tracked. For over 25 years after the Montreal Protocol was signed, the atmospheric abundance of ozone-depleting gases changed mostly as expected, responding to sharp decreases in reported amounts produced by all countries in the world. Initial signs of ozone recovery were becoming detectable. But around 2015, it became clear that the second most abundant ozone-depleting chemical, CFC-11 (CFCl3), was sharply diverging from its expected trajectory. Fortunately, the anomaly was detected in NOAA’s global atmospheric measurement network. At first, scientists struggled to understand the slowdown in the concentration decline being observed for CFC-11; was the global atmosphere’s cleansing ability changing, perhaps in response to increased greenhouse gas abundances, or was the Montreal Protocol being violated on a large scale? In this presentation, I’ll describe the unraveling of that detective story, highlighting how the available clues provided by high-precision chemical analysis tools, an understanding of atmospheric processes, and close ties to the international policymakers through the Montreal Protocol led to the identification of the first substantial violation of the Montreal Protocol and, ultimately, its apparent resolution. I will also spend some time reflecting on the factors that enabled this success story, and their implications for addressing other global issues caused in part by human emissions of long-lived gases, such as climate change. 

Seminar

CIRES

CU Boulder

Atmospheric Chemistry Program Seminar: Dr. Steve Montzka, NOAA