Rajendra Shende requested Dr. Newman to briefly explain for the benefit of the National Ozone Units around the world two recent and apparently contradictory observations relating to levels of stratospheric ozone depletion. One report appeared to be very positive; the other seemed to be a serious warning:
The loss of stratospheric ozone over Antarctica in September 2010 was one of the lowest on record.
A record loss of stratospheric ozone was recorded over the Arctic in March 2011.
Mr. Shende: “How should National Ozone Officers engaged in implementation of the Montreal Protocol, which is considered to be a grand success, explain this situation to their Ministers and their fellow countrymen?”
Dr. Newman: “This low Arctic ozone is very interesting, but in the long term the ozone layer will recover thanks to the Montreal Protocol. Without the Montreal Protocol, this year’s ozone destruction would most likely have been worse. The slow recovery of the ozone layer is due to the fact that ozone-depleting substances stay in the atmosphere for several decades.”
Mr. Shende: “It is stated that the loss observed is also due to the very low stratospheric temperatures. What are the reasons for low temperatures?”
Dr. Newman: “The Arctic stratosphere has been abnormally cold during March because of a lack of weather systems. In a typical winter, we see a number of very large scale weather systems that move upward from the lower atmosphere, the troposphere, into the stratosphere. These weather systems warm up the Arctic during the winter and spring. Surprisingly, these weather systems have been rather weak this winter. The reason for the lack of weather systems is an area of active research.”
Mr. Shende: “UNEP and WMO early this year released the ‘Report of 2010 Assessment of the Scientific Assessment Panel’ which provides an objective synthesis of the impending recovery of Ozone Layer. How does this synthesis match with these recent observations?”
Dr. Newman: (emphatically) “This loss does not change the conclusion of Scientific Assessment Panel that Arctic ozone will continue to increase as chlorofluorocarbons (CFCs) decrease. The Montreal Protocol is an international treaty adopted under the UN umbrella in 1987 to protect the ozone layer – banning the production of ozone-depleting CFCs worldwide today. CFCs released during prior decades however, will take many decades to disappear. Until that time Arctic ozone levels are vulnerable, essentially depending on the year-to-year variations in March-April Arctic stratospheric temperatures at altitudes around 20 km.
It’s like an upset of a great soccer team – events occasionally happen to cause a great team to be poor while a poor team is great. In the end, it’s the entire season that counts.”