Briefs: The hole truth

The closely monitored ozone hole above Antarctica is renowned for its unpredictable seasonal behaviour and changes in shape. High-altitude clouds form above Antarctica as soon as the temperature goes below -85°C in winter and spring, seasons during which the hole is at its peak. In spring, sunlight warms the stratosphere and the hole opens up. In its January 22, 2004 issue, Nature has published an article entitled "How can we tell if the Montreal Protocol is working?" The article provides an insight into the lifespan (estimated at 50 years) of CFC-11 and the slow decrease in stratospheric levels of it. The gap between Northern and Southern hemisphere levels of CFC-11 is closing thanks to declining emissions and atmospheric mixing, demonstrating that the Montreal Protocol is working — slowly but surely. The World Ozone and Ultraviolet Radiation Data Centre provides images based on satellite records: