The Montreal protocol mitigates climate change

Since 1 January 1989, the signatories of the Montreal Protocol have curbed their production and consumption of CFCl₃, CF₂Cl₂, and other ozone-depleting substances (ODS). The Antarctic ozone hole continues to form every year and let harmful radiation reach the surface. In some years, ozone levels also drop alarmingly in the Arctic. Even so, observations suggest Earth’s beleaguered ozone layer is beginning to recover. According to a new study, the protocol is also providing the polar regions with some protection from another threat: climate change. Olaf Morgenstern of Cambridge University and his colleagues have simulated what Earth’s climate would be like in 2025 if levels of ODS had continued to rise unchecked since 1989. Ozone depletion affects circulation and climate in the stratosphere and, through coupling, in the atmosphere closer to Earth’s surface. The Cambridge model predicts an annual mean warming of around 1 K in the polar regions and a remarkable springtime warming of 2–3 K in the lee of the Antarctic Peninsula. In the Arctic, Canada and Greenland warm considerably more than northern Siberia. The predicted high-latitude patterns resemble observed temperature trends, suggesting a depleted ozone layer could modulate climate change. Morgenstern and his colleagues conclude, “The Montreal Protocol has provided an enormous benefit not only to the stability of the stratospheric ozone layer but also to surface climate.” (O. Morgenstern et al. , Geophys. Res. Lett. , in press.)