The hole in the Antarctic ozone layer is approaching the all-time record of 2003 and it is unclear whether the world will ever attain full recovery of the naturally occurring trace gas that shields it from cancer-causing ultraviolet (UV) radiation, according to the United Nations meteorological agency.
“Full recovery of the ozone layer is not expected until the middle of this century, when atmospheric chlorine and bromine are expected to drop below the threshold for the formation of an Antarctic ozone-hole,” UN World Meteorological Organization (WMO) Secretary-General Michel Jarraud said of the campaign to eliminate the use of ozone-destroying chemicals.
“However, it is in fact uncertain whether we may ever reach full ozone recovery,” he added of the layer that filters out ultraviolet radiation that can cause skin cancer, cataracts and other diseases, noting that the latest findings showed the hole close to the 2003 record of 28 million square kilometres.
Given the uncertainties he called for more extensive integration of ground-based observations, satellite observations and numerical modelling.
“The campaign to protect the ozone layer represents an extraordinary success story, but until emissions of CFCs and other ozone-depleting substances are reduced to zero, saving the ozone layer will remain unfinished business,” said Klaus Toepfer, Executive Director of the UN Environment Programme (UNEP), whose Ozone Secretariat supports the Montreal Protocol and Vienna Convention on phasing out ozone-destroying chemicals such as chlorofluorocarbons (CFCs).
Recovery of the ozone layer is divided into three phases, the first being when depletion is less rapid than before. It is here that the Antarctic hole has yet to show signs of improvement. Published results indicate less rapid ozone loss in some areas of the world, but year-to-year variations in meteorological conditions in the stratosphere cause variations in the extent of ozone destruction.
This interannual “noise” makes it difficult to determine whether the minimum has been reached and the start of phase two has begun, WMO said. At least 5-10 more years of observations will be necessary. The second phase is when minimum levels have been reached and the ozone starts to increase again. The third, known as full recovery, is when total ozone has returned to pre-1980 levels, that is before the ozone hole started to form.
In recent years, scientists have become increasingly aware of possible links between ozone depletion and climate change. Increased atmospheric concentrations of greenhouse gases (GHGs) will lead to a warmer climate at the Earth’s surface. At altitudes where we find the ozone layer, the same increase in GHGs is likely to lead to a cooling of the atmosphere, enhancing the chemical reactions that destroy ozone.
At the same time, the amount of water vapour in the stratosphere has been increasing at the rate of about 1 per cent per year. A wetter and colder stratosphere means more polar stratospheric clouds, which is likely to lead to more severe ozone loss in both polar regions.
These observed changes could delay the expected recovery of the ozone layer. It is therefore vital that all nations with stratospheric measurement programmes continue to enhance these measurements and that funding agencies continue to support research on stratospheric ozone and harmful UV radiation, WMO said.