Title: On science informing international policy: Are emissions of a banned ozone-depleting substance really increasing?
Abstract: Ongoing global-scale measurements of long-lived gases provide unique information for addressing important science and policy-relevant questions. As a recent example, results suggest that some entities may no longer be adhering to global controls on an ozone-depleting gas agreed to in the Montreal Protocol. The observational evidence is straightforward: the concentration of CFC-11, the second most abundant ozone-depleting gas, is no longer decreasing as fast as it was 5 years ago, and the slowdown started first in the northern hemisphere. These changes typically indicate increasing emissions, but this unsettling conclusion seemed highly unlikely, given that production of CFC-11 has reportedly been banned for nearly a decade. Equally implausible, however, was the alternative conclusion: that global atmospheric chemistry or dynamics had changed and altered the atmospheric decline of CFC-11. In this talk I’ll present and update the scientific evidence supporting the assertion that CFC-11 emissions and production have increased in recent years. I’ll also briefly describe the international response to this news, which is encompassed by a decision adopted earlier this month by the international community tasked with ensuring recovery of the ozone layer, the Parties to the Montreal Protocol.