Next: Nitrogen loading  Previous: Climate change  Contents

Stratospheric ozone depletion

Global consumption of chlorofluorocarbons (CFCs), the most prevalent ozone-depleting substances (ODS), fell from 1.1 million tonnes in 1986 to 160 000 tonnes in 1996 (see graph below), thanks to an almost complete phase out by industrialized countries (UNEP 1998a). Several factors contributed to the success of policies directed at reducing the consumption of ODS: damage to the ozone layer could be ascribed to a single group of substances, alternative substances and processes were developed at acceptable costs, a scientific assessment was introduced to make adjustments to the Montreal Protocol as required, the Protocol contained flexible implementation schemes and evaluation procedures, and the principle of 'common but differentiated' responsibilities was recognized for the developed and developing countries.

Global CFC production (Click image to enlarge) Source: UNEP 1998a

CFC production has fallen from a peak of more than 1 million tonnes a year to 160 000 tonnes in 1996 as a result of the Montreal Protocol

One measure of the Protocol's success is that the ozone layer is now expected to recover to pre-1980 levels by the year 2050. Without the Protocol, levels of ODS would have been five times higher then than they are today, and surface UV-B radiation levels would have doubled at mid-latitudes in the northern hemisphere (UNEP 1999).

The total combined abundance of ODS in the lower atmosphere peaked in about 1994 and is now slowly declining (WMO, UNEP, NOAA, NASA and EC 1998). While total chlorine is declining, total bromine is still increasing, as is the abundance of CFC substitutes. If reductions in the use of ODS continue as envisaged in the Montreal Protocol, then concentrations of these substances in the stratosphere should have peaked between 1997 and 1999, and should begin to decline during the next century. The rate of decline in stratospheric ozone levels at mid-latitudes has already started to slow. The unusually low ozone values above the Arctic in late winter/spring observed in six out of the past nine years could have been accentuated by the unusually cold and prolonged stratospheric winters experienced during those six years (WMO, UNEP, NOAA, NASA and EC 1998).

Challenges in the protection of the ozone layer   CFC production in developing countries, notably Brazil, China, India, Republic of Korea, Mexico and Venezuela, more than doubled between 1986 and 1996, while consumption rose by some 10 per cent (UNEP 1998a). Because production levels in the years 1995-97 will be used as base levels to determine the timing of phase out in developing countries, scheduled to begin in mid-1999 with elimination due by 2010, the current high production will inflate the allowed levels of production for years to come. The Russian Federation will not eliminate its production of CFCs before the year 2000, and some of the European transition economies are experiencing economic and technical difficulties with CFC substitution (UNEP 1998c). Halon production, mostly for use in fire-fighting equipment, is rising again, primarily in developing countries. For example, production of halons in China grew nearly fourfold between 1991 and 1996 (UNEP 1998a). This trend is of particular concern since a given amount of halons can destroy up to ten times more ozone than the same amount of CFCs. CFC elimination is being undermined by a rise in illegal trading. Substantial demand still exists in the developed world, mostly to service existing refrigeration and cooling equipment. Illegally-imported virgin CFCs are cheaper than legally recycled CFCs or new CFCs obtained from limited existing stocks. The incentives for smuggling are therefore high. Estimates of the size of the global CFC black market range from 20 000 to 30 000 tonnes annually.

Despite significant progress in bringing the problem of ozone-layer depletion under control, a number of outstanding challenges remain (see box right). Past (and continuing) emissions of ODS will result in increases in UV-B radiation that are likely to lead to increases in the incidence and severity of a variety of short- and long-term human health effects, particularly on the eyes, the immune system and the skin. Recent evaluations of UV-related excess skin cancer risks in Europe caused by ozone depletion suggest that, even though stratospheric ozone concentrations should reach a minimum around the year 2000 (which assumes that the measures in force are fully implemented), excess skin cancer incidence is not expected to begin to fall until about 2060, because of the time lags involved.

The response of terrestrial ecosystems to increased UV-B is evident primarily in interactions among species rather than in the performance of individual organisms. Recent studies indicate that increased UV-B affects the balance of competition among higher plants, the degree to which higher plants are consumed by insects and the susceptibility of plants to pathogens (UNEP 1998b). Increased UV-B can be damaging for crop varieties but this may be offset by protective and repair processes.

Current ozone losses and UV-B increases     ozone UV-B   loss (%) increase (%) Northern hemisphere, mid-latitudes, winter/spring 6 7 Northern hemisphere, mid-latitudes, summer/autumn 3 4 Southern hemisphere, mid-latitudes, year-round 5 6 Antarctic spring 15 22 Note: figures are approximate and assume other factors, such as cloud cover, are constant Source: WMO, UNEP, NOAA, NASA AND EC (1998)

In terms of overall impact, ozone depletion interacts with the climate change process. Stratospheric loss of ozone has caused a cooling of the global lower stratosphere: changes in stratospheric ozone since the late 1970s may have offset about 30 per cent of the warming effect of other greenhouse gases over the same period (WMO, UNEP, NOAA, NASA and EC 1998). There are also complex interactions between ozone depletion, climate change and the abundance of methane, nitrous oxide, water vapour and sulphate aerosols in the atmosphere. For example, carbon is an important element in the absorption of UV radiation. Climate change and acid rain have led to decreases in the dissolved organic carbon concentration in many North American lakes (Schindler and others 1996). As organic carbon levels have decreased, UV radiation has been able to penetrate much more deeply into surface waters, resulting in greater UV-B exposure of fish and aquatic plants.

While the potential impact of stratospheric ozone depletion means there is no room for complacency, the cooperative measures that followed the identification of the problem remain an outstanding and encouraging example of the ability of the international community to act in unison in protecting the global environment.

Next: Nitrogen loading  Previous: Climate change  Contents