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WORLD METEOROLOGICAL ORGANIZATION |
UNITED NATIONS ENVIRONMENT PROGRAMME |
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3. CURRENT STATUS OF THE GLOBAL OZONE OBSERVING SYSTEM AND MONITORING OF THE UV-B AND ASPECTS OF ATMOSPHERIC OZONE SCIENCE AND RESEARCH
Under this agenda item the meeting heard with interest reviews of the current state of ozone research and systematic observations (presented by Dr Rumen D. Bojkov) and on UV-B potential impacts (presented by Dr Jan C. Van der Leun) which are summarized below. These were preceded by an overview of the WMO Global Atmosphere Watch (GAW) system for environmental monitoring and research (presented by Dr John M. Miller).
3.1 There has been considerable progress in our understanding of stratospheric processes since the last report. This has been achieved through intense national and international efforts both in terms of routine measurements and specific more intense observational campaigns, together with developments in theoretical understanding and numerical models. The ability to stimulate and predict ozone change has improved with three new dimensional modelling capabilities now available. However, although good progress has been made uncertainties in the scientific details remain particularly with regard to ozone loss at middle latitudes, sources and sinks of some ozone depletory, notably methyl bromide, and the microphysical and chemical processes associated with ozone depletion.
3.2 There has been a marked increase in the number of UVB monitoring sites both for broadband and spectral measurements and progress is being made towards better coordination and standardization of such measurements. By contrast there have been only very limited improvements in our understanding and ability to quantify the effects of increased UVB radiation with all of the recommendations that were made in the last report remaining unfulfilled.
3.3 Dr Bojkov provided a most comprehensive review of the state of the ozone layer. He emphasized that the atmospheric observations, laboratory investigations and theoretical and modelling studies of the past few years have provided deeper understanding of the anthropogenic and natural chemical changes in the atmosphere and their relation to the decline in the Earth's ozone and possible effects on the radiative balance of the climate system. These studies indicate that the byproducts of human made CFCs and halons are the culprit for the Antarctic ozone destruction and support preventive actions agreed by the Montreal Protocol aimed at recovery to the natural state of the ozone layer sometime in the second half of the 21 century. The highlights of the main points made by Dr Bojkov are summarized in the following paragraphs.
3.4 The total ozone decline, which started in the 1970's, continues. It is statistically significant all year round except over the 20°N-20°S tropical belt. The GOODS quality-controlled data from more than 40 stations with long-term observations supplemented by another 100 stations and satellites operating during the last 20 years show that the ozone decline over the middle and polar latitudes is close to 10 per cent relative to the ozone levels of 1950s and 1960s. Taking into account known natural variability (e.g. annual and solar cycles, the Quasi-Biennial Oscillation), the decline in both hemispheres is especially strong during the winter-spring ( > 6-7 per cent per decade) and is only half that during the summer autumn seasons. Detailed studies show a statistically significant increase in the rates of the negative ozone trends by ~1.5-2.0 per cent during 1981 - 1991, compared with 1970-1980. The ozone loss is latitudinally and longitudinally non-symmetrical which in a long-run may have important circulational consequences.
3.5 Numerical expressions of ozone trends over a few major
regions as linear trend since 1970 (panel a) and over the middle latitudes and
the northern and southern polar regions since 1979 (panel b) are shown in Table
1 where the minus signs are omitted! The estimated error is given as ±2
but it is seen that the declining rates are significant to more than 3
(99% confidence) and this is therefore, further confirmation of the validity
of the global character of the ozone decline. An acceleration of the negative
trends during the past 15 years is obvious from Table 1. The year-round trend
for the globe since 1980s is ~ -3.5±0.4 percent per decade.
3.6 The main ozone losses occur in the lower stratosphere, where over middle latitudes, especially during November-May, the partial ozone decline has exceeded 20 per cent during the last two decades. At the same time all European and Japanese ozone sounding stations show increase of the tropospheric ozone especially strong during the 1960s through the 1980s which should have a significant radiative impact.
3.7 There is strong evidence that ozone concentrations in the boundary layer over populated regions of the northern hemisphere have augmented by more than 50 per cent during the past 30 years, owing the photochemical production from anthropogenic precursors (e.g. CO, NOx, hydrocarbons) (e.g. WMO, 1994). It is further documented that export of ozone from North America is a significant source for the North Atlantic region during summer. It has also been shown that biomass burning is a significant source of ozone (and carbon monoxide) in the tropics during the dry season. An increase in UV-B radiation (e.g. from stratospheric ozone loss) is expected to alter the concentrations of some chemically and climatically important tropospheric constituents such as OH, CO, and CH4. This may cause a decrease of tropospheric ozone in the background-clean troposphere but, in some cases, it will increase production of ozone in more polluted regions. Many processes affecting troposhperic ozone balance are not adequately represented or tested in the models and the accuracy of these projections is therefore limited.
)
using GO3OS data, Jan 1964 to March 1994
| Dec. Jan. Feb. March | May,
June, July, Augu. | Sept. Oct. Nov. | |||
|---|---|---|---|---|---|
| Regions | Latitude | (a) linear trend fit since 1970 | Year | ||
| Arctic | 60-80°N | 3.7 ± 2.0 | 2.2 ± 0.9 | 1.3 ± 1.0 | 2.8 ± 1.1 |
| Western Siberia | 56°N | 3.8 ± 2.0 | 2.3 ± 1.2 | 3.2 ± 1.4 | 3.3 ± 1.1 |
| Eastern Siberia And Far East | 53°N | 3.2 ± 1.8 | 1.9 ± 1.8 | 2.6 ± 1.5 | 2.8 ± 1.2 |
| European Rus. Fed. | 52°N | 5.3 ± 2.0 | 2.8 ± 1.2 | 3.0 ± 1.3 | 3.9 ± 1.0 |
| Dobson Europe | 40-59°N | 3.9 ± 1.6 | 1.2 ± 0.9 | 1.0 ± 1.0 | 2.3 ± 0.8 |
| North America | 46°N | 3.0 ± 1.0 | 2.1 ± 0.8 | 1.1 ± 0.6 | 2.2 ± 0.6 |
| Central Asia | 42°N | 2.9 ± 1.5 | 1.2 ± 1.4 | 2.5 ± 1.2 | 2.1 ± 0.9 |
| Antarctica | 65-90°S | 4.2 ± 1.0 | 3.7 ± 2.0 | 16.6 ± 2.2 | 7.3 ± 1.2 |
| (b) linear trend fit since 1979 | |||||
| Arctic | 7.5 ± 3.8 | 4.4 ± 1.8 | 3.6 ± 2.2 | 5.6 ± 2.0 | |
| 35° - 60°N | 6.8 ± 2.4 | 3.8 ± 1.5 | 2.5 ± 1.0 | 4.5 ± 1.2 | |
| 35° - 60°N | 3.6 ± 1.2 | 4.9 ± 1.3 | 7.3 ± 2.0 | 5.0 ± 1.0 | |
| Antarctica | 4.6 ± 2.4 | 22.1 ± 7.2 | |||
3.8 An accurate assessment of the radiative effect of ozone changes is limited by the lack of detailed information on the variation in vertical distribution of ozone with latitude and longitude. However, recent calculations (e.g. WMO 1994) support earlier conclusions that lower stratospheric ozone depletion in recent decades has resulted in a negative radiative forcing (i.e., a cooling effect on the climate) and has offset by about 15-20% the positive greenhouse forcing due to increases in other gases. The increase of tropospheric ozone since pre-industrial times may have enhanced the total greenhouse forcing by as much as 20%. The tropospheric ozone increase from the 1970s to the 1980s has caused positive radiative forcing equal to the forcing due to the changes of all other greenhouse gases during the same period. Such changes could have an impact on the radiative balance of the earthatmosphere system and the thermal structure of the atmosphere and thus cause as yet unpredictable changes to atmospheric circulation patterns.
3.9 The drastic (by over one third) decline of total ozone over the Antarctic appearing during the austral-spring season since the early 1980s when the total ozone amount decrease to less than 200 m atm cm and commonly called "ozone hole" continues with new strength. Ozone values in August 1995 were generally 25% to 30% below the pre-ozone-hole averages. The ozone layer over the Antarctic during the austral-spring of 1995 underwent massive destruction especially during the second half of September and October when the deficiency was about 50% from the pre-ozone-hole 1957-1979 average and for a few days reached 70%. Starting at the end of September and lasting for a period of six consecutive weeks, the balloon soundings at Marambio, Neumayer and Syowa indicated nearly complete annihilation of the ozone at altitudes between 14 and 20 kilometres. During this period, the spread of the ozone hole (area covered with less than 220-200 m atm cm of total ozone) exceeded 20 million km2 (about twice the area of Europe) which lasted an unprecedented 40 days. Comparing the number of days when the ozone hole covered area exceeded 15 million km2 during the past 5 years shows that the 1995 event was the longest lasting. In 1991 there were - 32 days; in 1992 - 49; in 1993 - 63; in 1994 - 55 and in 1995 - 71 !. The ozone hole event in 1995 did not disappear until early December and thus was the longest lasting on record.
3.10 In the Northern Hemisphere middle and polar latitudes during the first three months of the winter-spring season (December-January-February of 1996) the average ozone amount was about 5 to 10% below the long-term (1957-1979) averages. This corresponds to the ozone level decline expected due to human made CFCs by linearly extending the observed trend since the early 1970s. With this background however during many days in January, mid February and March over the region from Greenland - Scandinavia to the western part of the Russian Arctic there was ozone deficiency exceeding 15- 20%. Ozone values of below 250 m atm cm were recorded for many days. In contrast with the Antarctic, the extremely low ozone values in the Arctic lasted for weeks but not months. The polar stratospheric vortex with its extremely cold lower stratosphere was dominant over the same region and obviously the low temperatures facilitated the ozone destruction processes in the presence of ClO. Record setting ozone deficiencies of -20 to -35 percent were also observed in 1995 winter-spring especially over Siberia and in both 1992 and 1993 winter-springs over North America, Europe and Siberia. It is obvious that during the winter-spring seasons when the equatorial stratospheric winds (QBO) are in their westerly phase the ozone deficiencies are greater.
3.11 Dr J.C. Van der Leun briefly reviewed the environmental effects of ozone depletion. He noted that an increase in UV-B radiation could have impacts on human and animal health, terrestrial plans, aquatic ecosystems, biogeochemical cycles, air quality and materials. Impacts in all these areas are discussed in the 1994 Assessment on Environmental Impacts of Ozone Depletion (UNEP), which was also published as a special issue of Ambio (May, 1995). Such impacts are the main reason for people to be interested in depletion of the ozone layer. He noted that there are well-developed programmes for research on atmospheric processes, and on measurement of UV radiation but unfortunately very little on effects.
3.12 Progress in effects research is slow, yet, there are indications that even with full implementation of the agreements to protect the ozone layer, there will still be significant effects. Lack of knowledge makes it impossible to develop mitigation strategies and priority setting. The potentially important coupling of the problems of ozone depletion and global warming - by UV damage to phytoplankton, cannot be quantified because there is insufficient knowledge on the damage response of phytoplankton to UV.
3.13 Dr Van der Leun concluded by stating that research funding for effects studies is disproportionally low, and it is urgent that this be changed. That will also be an effective way to sustain public support for the efforts to protect the ozone layer.
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