Ozone (O3) gas is an unstable form of oxygen (O2) and is created by natural processes such as ultraviolet radiation in the upper atmosphere and by lightning. Ozone plays a key role in the atmosphere. The ozone layer absorbs a portion of the radiation from the sun, preventing it from reaching the planet's surface. It absorbs the portion of ultraviolet light called UVB. UVB has been linked to many harmful effects, including various types of skin cancer, cataracts, and harm to some crops, certain materials, and some forms of marine life.

Ozone molecules are constantly formed at any given time and destroyed in the stratosphere. The total amount remains relatively stable. While ozone concentrations vary naturally with sunspots, the seasons, and latitude, these processes are well understood and predictable. Each natural reduction in ozone levels has been followed by a recovery. Scientific evidence has shown that the ozone shield is being depleted well beyond changes due to natural processes.

The ozone layer acts like a giant sunshade. It protects plants and animals from much of the sun's harmful ultraviolet radiation. It shields plants and animal life from UVB, which, in high doses of incidence, can be particularly damaging to environment and natural life. The absorption of UVB by the ozone layer also creates a source of heat, which plays a key role in the temperature structure of the atmosphere.

Ozone layer depletion is a threat to humanity and all living organisms. Ozone layer depletion seems likely to increase the rate of greenhouse warming, by reducing the effectiveness of the carbon dioxide sink in the oceans. Phytoplankton (micro-organisms) in the oceans assimilates large amounts of atmospheric carbon dioxide. Increased UV radiation reduces phytoplankton activity significantly. This means that large amounts of carbon dioxide remain in the atmosphere.

Increasing amounts of UV radiation have an impact on plankton and other tiny organisms at the base of the marine food web. These organisms provide the original food source for all other living organisms in the oceans. A high increase in UV radiation may disrupt many ecosystems on land. Rice production may be drastically reduced by the effects of UVB on the nitrogen assimilating activities of micro-organisms. With a diminishing ozone layer, it is likely that the supply of natural nitrogen to ecosystems, such as tropical rice paddies, will be significantly reduced.

Most plants (and trees) grow more slowly and become smaller and stunted when exposed to large amounts of UVB. Increased UVB also inhibits pollen germination.

The protection of the earth's ozone layer is one of the major challenges over the past 30 years, spanning the fields of environment, trade, international cooperation and sustainable development. The thinning of the ozone layer threatens human health through diseases such as skin cancer, eye cataracts and immune deficiency, affects flora and fauna, and also influences the planet's climate. Ozone depletion is brought about by a number of chemicals known as ozone depleting substances (ODS), the most notorious of which are the chlorofluorocarbons (CFCs).

CFCs, created by humans, are a main cause of the hole in the ozone layer, which permits ultraviolet (UV) radiation to hit the earth surface. This radiation can also damage plant and marine life. Scientists believe that the development of ozone layer hundreds of million years ago allowed the evolution of complex life forms on earth.

Worldwide, CFCs are declining because of the control on their use under the Montreal Protocol, especially among the countries with the heaviest use from 1986 to 1998. Cape Grimm Global Atmosphere Watch Monitoring Station located in Australia measures worldwide CFCs on the troposphere, the lowest layer of the atmosphere, which extends to the ground about 6 miles above sea level.

International cooperation has been the key to protecting the stratospheric ozone layer. Nations agreed in principle to tackle a global problem before its effects became evident or its existence scientifically proven.

In 1977, the United States banned use of CFCs in non-essential aerosols. Canada, Norway and Sweden enacted similar control measures. The European Community (EC) froze production capacity and began to limit use of aerosols. These initiatives, though useful, provided only a temporary respite. After falling for several years, CFC consumption began increasing again in the 1980s, as non-aerosol uses, such as foam blowing, solvents and refrigeration, increased. Stricter control measures were needed and UNEP and several developed countries took the lead, calling for a global treaty on stratospheric ozone layer protection (Benedick 1998).

Due to continuous efforts by the international communities the global consumption of ODS has decreased markedly and the ozone layer is predicted to start recovering in the next one or two decades and to return to a pre-1980 level by the middle of the 21st century of all the future control measures of the Montreal Protocol are adhered to by all countries (UNEP 2000a).

India and China are the largest regional producers and users of CFCs. China's consumption of ODS increased more than 12 percent per year during 1986-94. India is the second largest producer and the fourth largest consumer of CFCs in the world (UNEP 1998). The Multilateral Fund of the Montreal Protocol and GEF have been helping the region meet the goals of the Montreal Protocol. China has made a commitment to phase out the consumption of ODS by 2010. It has already banned the establishment of new CFC- and halon-related production facilities, and developed general and sector-specific plans with the help of the World Bank and the Multilateral Fund. The latter has approved a World Bank project which will help India phase out CFC production by 2010.

Bangladesh accessed the protocol on August 2, 1990. Until August 19, 2004 Montreal Protocol was ratified by 187 countries. Through ratification/ accession to the protocol, government is committed to protecting the ozone layer by phasing out the use of ozone-depleting substances within fixed period of time. As per Montreal Protocol maximum allowable limit of use of ODS for Bangladesh is 580.4 MT (Metric Tons) up to December 2004, 290.2 MT up to December 2007, 087.1 MT up to December 2009 and 000.0 MT for January 2010.

In 1994, the United Nations General Assembly voted to designate September 16 as "World Ozone Day", to commemorate the signing of the Montreal Protocol on that date in 1987.

Bangladesh is going to observe the International Ozone Day on 16 September along with other countries of the world. Through observance of the International Ozone Day it would be possible to create awareness among people to protect the ozone layer and this will ensure sustainable and livable environmnet for all .

The writer is a senior assistant secretary of the Ministry of Environment and Forest and is a reelance contributor to The Daily Star.