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Learning Center on Caribbean Weather and Climate |
Ozone depletion |
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Ozone depletion at high latitudes is one of the most striking global environmental problems caused by anthropogenic emissions. The observation of low total ozone columns over Antarctica greatly surprised the scientific community. Explanations for the low ozone columns included, e.g. changes in solar activity, e.g. changes in the large-scale circulation patterns in the atmosphere. Freons (also known as chlorofluorocarbons or CFCs) were also proposed as a cause, although the existing theories did not support this. The observed low total ozone columns over Antarctica were though to be erroneous and therefore eliminated from the satellite records. At the same time with the formulation of a new theory, a large international Antarctic research study was carried out in 1987. The study suggested that chlorine originating from freons was the cause of the detected massive ozone destruction. Outside the polar regions free chlorine released from freons is captured by reservoir gases (e.g. hydrogen chloride (HCl) and chlorine nitrate (ClONO2)) preventing large-scale chlorine catalysed ozone destruction. However, in the polar winter and spring atmospheres, polar stratospheric clouds serve as surfaces for capturing free nitrogen oxides from the atmosphere and lead to the release of chlorine from reservoirs. Cold temperatures, below –78 °C, are needed for the formation of polar stratospheric clouds. Cold airmasses are found inside large-scale low-pressure areas (called polar vortices) in winter polar stratospheres. (Read more for example from Question 6. and Question 8. of the Twenty Questions and Answers About the Ozone Layer) The stratosphere contains 90% of the atmospheric ozone, and the remaining 10% is in the lower atmosphere, the troposphere. In the troposphere, high concentrations of ozone may negatively affect human health, forests and agriculture. The lower atmospheric ozone concentrations have been increasing in many parts of the world due to enhanced emissions of nitrogen oxides, hydrocarbons and carbon monoxide. These emissions are mainly originating from traffic, energy production and from biomass burning. Both stratospheric and tropospheric ozone have an effect on climate, because of the infrared and ultraviolet radiation absorption properties of ozone. Learn more about ozone science from the "Executive summary of Scientific Assessment of Ozone Depletion: 2002" published by the Ozone Secretariat of UNEP/WMO or take the Ozone Hole Tour of the University of Cambridge. Download The Ozone Story cartoon! Back to top of this pageGlobal efforts to protect the ozone layer are based on two international agreements. The Vienna Convention 1985 provided for scientific and technical co-operation, and laid the groundwork for the Montreal Protocol. The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted by governments in 1987. It has been modified four times to include an increasing number of ozone-depleting substances, to strengthen the phase out schedules and to improve effective implementation of its provisions. The amendments were adopted in London (1990), Copenhagen (1992), Montreal (1997) and Beijing (1999). The Protocol aims to reduce and eventually eliminate the emissions of man-made ozone-depleting substances. In 2003 there were 184 parties to the Protocol. The Montreal Protocol is successful because of regular revision of the requirements on the basis of the latest scientific and technical information provided by the assessment panels. This has enabled the Parties to react quickly to the new information with appropriate policy measures. The Protocol has common but differentiated responsibilities for developed countries and developing countries. An important part of the Protocol is the Multilateral Fund, the financing mechanism which assists developing countries in meeting their requirements. Industrialized countries have phased out the production and consumption of freons, halons, methyl chloroform, carbon tetrachloride and hydrobromofluorocarbons, and phase-out dates have been agreed for the remaining controlled substances, hydrochlorofluorocarbons and methyl bromide (See Phase-out schedule). Developing countries generally have a 10-year grace period beyond the phase out dates for industrialised countries. Certain productions or uses are exempted from the phase-out requirement, such as essential and critical uses and production for basic domestic needs of developing countries. Read more about the Montreal Protocol from the web site of the Ozone Secretariat of UNEP/WMO and find out if your country has ratified the Protocol! Read the article by Hezra C. Medica originally published at "Antigua Sun" as an additional Caribbean point of view. The article was copied here from the SIDSnetSite (http://sidsnet.org/latestarc/climate-newswire/msg00117.html). Back to top of this pageAs a result of the Montreal Protocol, the increasing trend of freon concentrations in the lower atmosphere has been slowing during recent years. Even a declining trend in some compounds has been measured. Freons and halons break up in the stratosphere, leading to the release of ozone-destroying chlorine and bromine. Despite the success of the Montreal Protocol, the long lifetimes of freons and halons lead the stratospheric concentrations of chlorine and bromine to stay at high levels in the coming decades. Extensive ozone depletion may therefore be detected during the next two decades or so. The ozone depletion phenomenon itself is expected to be detectable until the middle of the 21st century. According to recent scientific results, climate change is also expected to affect stratospheric climate and ozone depletion efficiency. With the carbon dioxide concentration of the atmosphere increasing, the lower atmosphere will become warmer and the upper atmosphere colder. These changes have already been measured. The cooling of the stratosphere will further stabilize the polar vortices which may lead to enhanced ozone depletion. This, in turn, would lead to enhanced UV radiation in the springtime. Back to top of this pageAdditional ozone resources in the net
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