Ozone depletion: Serious threat to biodiversity
THE OZONE layer is a thin layer which protects the earth from dangerous ultraviolet rays. When this layer becomes thinner or damaged, the ultraviolet radiation reaches to earth and can cause eye cataract, skin cancer, and mutation to humans, reduce crop yield and damage arable land. The ozone layer is a region high in the stratosphere, containing ozone (a form of oxygen, O3), located in the stratosphere in a region that is 10 to 50 km above the Earth (lower near the poles), with the highest ozone concentrations in a region that is variously called the lower stratosphere, the tropopause, or simply the “ozone layer”.
The ozone layer is essential to life on earth, as it absorbs harmful ultraviolet-B (UV-B) radiation from the sun. In recent years the thickness of this layer has been decreasing, leading in extreme cases to holes in the layer. Measurements carried out in the Antarctic have shown that at certain times, more than 95 per cent of the ozone concentrations found at altitudes of between 15 and 20 km and more than 50 per cent of total ozone are destroyed, with reductions being most pronounced during winter and in early spring. Natural phenomena, such as sun-spots and stratospheric winds, also decrease stratospheric ozone levels, but typically not by more than 1 to 2 per cent.
The main cause of ozone layer depletion is the increased stratospheric concentration of chlorine from industrially produced CFCs,
halons and selected solvents. Once in the stratosphere, every single chlorine atom can destroy up to 100,000 ozone molecules. The amount of damage that an agent can do to the ozone layer is expressed relative to that of CFC-11 and is called the Ozone Depletion Potential (ODP), where the ODP of CFC-11 is 1.
Biodiversity has been defined by as “the total variety of life on Earth.” This term can also be used to reflect the range of species at a site, the size of the gene pool, or even the number of different ecosystems on the planet. Biodiversity is important for sustainable development because it represents the wealth of biological resources available to us and future generations for food, clothing, medicine, and housing. Declining biodiversity is widely seen as one of the most serious environmental problems around the world today.
There are serious impacts of ozone depletion on biodiversity. For example, increased UV radiation reduces the levels of plankton in the oceans and subsequently diminishes fish stocks. It can also have adverse effects on plant growth, thus reducing agricultural productivity. A direct negative economic impact is the reduced lifespan of certain materials.
In forests and grasslands increased UV-B radiation is likely to result in changes in species composition (mutation) thus altering the bio-diversity in different ecosystems. Physiological and developmental processes of plants are affected by UV-B radiation, even by the amount of UV-B in present-day sunlight. Despite mechanisms to reduce or repair these effects and a limited ability to adapt to increased levels of UV-B, plant growth can be directly affected by UV-B radiation.
Phytoplankton form the foundation of aquatic food webs, Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net productivity. The position of the organisms in the euphotic zone is influenced by the action of wind and waves. Solar UV-B radiation has been found to cause damage to early developmental stages of fish, shrimp, crab, amphibians and other animals, and their habitats. The most severe effects are decreased reproductive capacity and impaired larval development. Even at current levels, solar UV-B radiation is a limiting factor, and small increases in UV-B exposure could result in significant reduction in the size of the population of animals that eat these smaller creatures.
Human activities since the start of the Industrial Era (around 1750) have caused increases in the abundances of several long lived gases, changing the radiative balance of Earths atmosphere. These gases, known as “greenhouse gases”, result in radiative forcing, which can lead to climate change. Other international assessments have shown that the largest radiative forcing come from carbon dioxide, followed by methane, troposphere ozone, the halogen containing gases, and nitrous oxide. All these forcing are positive, which leads to a warming of Earths surface. In contrast, stratospheric ozone depletion represents a small negative forcing, which leads to cooling of Earths surface. In the coming decades, halogen gas abundances and stratospheric ozone depletion are expected to be reduced along with their associated radiative forcing. The link between these two forcing terms is an important aspect of the radiative forcing of climate change.
An increased level of solar UV radiation is known to have adverse effects on synthetic polymers, naturally occurring biopolymers and some other materials of commercial interest. Synthetic polymers, naturally occurring biopolymers, as well as some other materials of commercial interest are adversely affected by solar UV radiation. Todays materials are somewhat protected from UV-B by special additives. Therefore, any increase in solar UV-B levels will therefore accelerate their breakdown, limiting the length of time for which they are useful outdoors.
Ozone depletion could be cured with care. A mechanism for the disposal and safe destruction of Ozone Depleting Substances (ODSs) and equipment containing ODSs does not reliably exists in many countries and should be implemented as soon as possible, with qualified and conscientious personal for the maintenance.
The effects of ozone depletion are real and of great global significance. It is important that we as individuals educate ourselves of the truths concerning the depletion of ozone. If each human in this world would be willing to make a small sacrifice for the greater good, the future of our ozone layer undoubtedly would be secure, which will result in preservation of biodiversity.