Another group of substances, hydrofluorocarbons (HFCs), were introduced as non-ozone depleting alternatives to support the timely phase-out of CFCs and HCFCs. HFCs are now widespread in air conditioners, refrigerators, aerosols, foams and other products. While these chemicals do not deplete the stratospheric ozone layer, some of them have high GWPs ranging from 12 to 14,000. Overall HFC emissions are growing at a rate of 8% per year and annual emissions are projected to rise to 7-19% of global CO2 emissions by 2050. Uncontrolled growth in HFC emissions, therefore, challenges efforts to keep global temperature rise at or below 2C this century. Urgent action on HFCs is needed to protect the climate system.
With the full and sustained implementation of the Montreal Protocol, the ozone layer is projected to recover by the middle of this century. Without this treaty, ozone depletion would have increased tenfold by 2050 compared to current levels, and resulted in millions of additional cases of melanoma, other cancers and eye cataracts. It has been estimated, for example, that the Montreal Protocol is saving an estimated two million people each year by 2030 from skin cancer.
The phaseout of controlled uses of ozone depleting substances and the related reductions have not only helped protect the ozone layer for this and future generations, but have also contributed significantly to global efforts to address climate change; furthermore, it has protected human health and ecosystems by limiting the harmful ultraviolet radiation from reaching the Earth.
A number of commonly used chemicals have been found to be extremely damaging to the ozone layer. Halocarbons are chemicals in which one or more carbon atoms are linked to one or more halogen atoms (fluorine, chlorine, bromine or iodine). Halocarbons containing bromine usually have much higher ozone-depleting potential (ODP) than those containing chlorine. The man-made chemicals that have provided most of the chlorine and bromine for ozone depletion are methyl bromide, methyl chloroform, carbon tetrachloride and families of chemicals known as halons, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs).
The scientific confirmation of the depletion of the ozone layer prompted the international community to establish a mechanism for cooperation to take action to protect the ozone layer. This was formalized in the Vienna Convention for the Protection of the Ozone Layer, which was adopted and signed by 28 countries, on 22 March 1985. In September 1987, this led to the drafting of The Montreal Protocol on Substances that Deplete the Ozone Layer.
The principal aim of the Montreal Protocol is to protect the ozone layer by taking measures to control total global production and consumption of substances that deplete it, with the ultimate objective of their elimination on the basis of developments in scientific knowledge and technological information. It is structured around several groups of ozone-depleting substances. The groups of chemicals are classified according to the chemical family and are listed in annexes to the Montreal Protocol text. The Protocol requires the control of nearly 100 chemicals, in several categories. For each group or annex of chemicals, the Treaty sets out a timetable for the phase-out of production and consumption of those substances, with the aim of eventually eliminating them completely.
When did we realize ozone depletion was an issue, and how did we fix it By 1985, the globe had already seen advancements in the scientific understanding of ozone depletion and its impacts on human health and the environment. It was then that the Vienna Convention for the Protection of the Ozone Layer was created in response. This agreement is a framework convention that lays out principles agreed upon by many parties. It does not, however, require countries to take control actions to protect the ozone layer. This would come later in the form of the Montreal Protocol.
The Vienna Convention was the first convention of any kind to be signed by every country involved, taking effect in 1988 and reaching universal ratification in 2009. This speaks to the enormity of ozone depletion at the time and the willingness of countries around the world to work together to solve it. The Convention aimed to promote cooperation among nations by exchanging information on the effects of human activities on the ozone layer. In doing so, the creators of the Convention hoped policymakers would adopt measures to combat those activities responsible for ozone depletion.
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. Exposure to solar UVB radiation has been shown to affect both orientation and motility in phytoplankton, resulting in reduced survival rates for these organisms. Scientists have demonstrated a direct reduction in phytoplankton production due to ozone depletion-related increases in UVB.
These reactions convert the inactive chlorine reservoir chemicals into more active forms, especially chlorine gas (Cl2). When the sunlight returns to the South Pole in October, UV light rapidly breaks the bond between the two chlorine atoms, releasing free chlorine into the stratosphere, where it takes part in reactions that destroy ozone molecules while regenerating the chlorine (known as a catalytic reaction). A catalytic reaction allows a single chlorine atom to destroy thousands of ozone molecules. Bromine is involved in a second catalytic reaction with chlorine that contributes a large fraction of ozone loss. The ozone hole grows throughout the early spring until temperatures warm and the polar vortex weakens, ending the isolation of the air in the polar vortex. As air from the surrounding latitudes mixes into the polar region, the ozone-destroying forms of chlorine disperse. The ozone layer stabilizes until the following spring.
Stratospheric ozone has been depleted by 5 to 6 percent at middle latitudes, but has somewhat rebounded in recent years. The largest recorded Antarctic ozone hole was recorded in 2006, with holes of slightly smaller size since then. Newman, Stolarski, and other colleagues have used their model to simulate how the real world ozone layer will recover as well. Because of climate change from greenhouse gases, they say, the ozone layer will probably not look exactly like it did in the 1970s.
NOAA scientists at the South Pole Station record the ozone layer's thickness by releasing weather balloons carrying ozone-measuring instruments called ozonesondes that measure the varying ozone concentrations as the balloon rises into the stratosphere.
The ozone layer acts as a natural filter, absorbing most of the sun's burning ultraviolet (UV) rays. Stratospheric ozone depletion leads to an increase in UV-B that reach the earth's surface, where it can disrupt biological processes and damage a number of materials.
Scientists have confirmed that non-melanoma skin cancer is caused by UV-B radiation, and further believe that a sustained 10% depletion of the ozone layer would lead to a 26% percent increase in non-melanoma skin cancer. This could mean an additional 300,000 cases per year world wide.
Cataracts are a clouding of the eye's lens and are the leading cause of permanent blindness world wide. They are a result of overexposure to UV. A sustained 10% thinning of the ozone layer is expected to result in nearly two million new cases of cataracts per year globally.
The ozone layer is very important for life on Earth because it has the property of absorbing the most damaging form of UV radiation, UV-B radiation. This has a wavelength of between 280 and 315 nanometres. As UV radiation is absorbed by ozone in the stratosphere, it heats up the surrounding air to produce the stratospheric temperature inversion that is shown in the following diagram.
Ozone is measured as the total amount that is present in a column of overlying atmosphere in Dobson units. One Dobson unit can be thought of as the amount of ozone that would be present if it formed a layer 0.01mm thick at average sea-level pressure and temperature. A typical Dobson reading for the ozone layer is about 300 Dobson units, meaning that the ozone layer would only be about 3mm thick if brought down to sea-level.
This method has been used to measure the ozone layer at Halley Research Station since 1956. In 1985, British Antarctic Survey scientists published results showing a steep decline in the levels of ozone over Halley since the 1970s, particularly during the austral spring, and the existence of the ozone hole was revealed. Since then, the extent of the ozone hole has been monitored continuously using both ground-based and satellite-based techniques.
The ozone hole has developed because people have polluted the atmosphere with chemicals containing chlorine and bromine. The primary chemicals involved are chlorofluorocarbons (CFCs for short), halons, and carbon tetrachloride. CFCs in particular were previously used for a wide range of applications, including refrigeration, air conditioning, foam packaging, and making aerosol spray cans. Because these chemicals are so inert, they are able to stay in the atmosphere long enough to be carried upwards to the stratosphere where they can damage the ozone layer.
Normally there are no clouds in the stratosphere because there is so little water vapour present. However, during the south polar winter, air in the stratosphere above Antarctica drops to temperatures below -80C! And this is enough to cause thin clouds to form. As long as it remains dark, nothing happens; but when spring arrives, UV radiation from the Sun reaches the Antarctic Circle and starts the process of chlorine release and ozone destruction. This continues until the stratospheric clouds disappear due to warming of the south polar atmosphere as summer approaches. By summertime, stratospheric air from lower latitudes is able to penetrate the polar latitudes, and thereby replenish the ozone layer above Antarctica. Hence, there is a seasonal cycle to the ozone hole over Antarctica with the lowest ozone levels recorded in late September and early October. 153554b96e