Ozone layer depletion is one of the significant environmental issues in the world. The newer studies indicating that the tropical ozone layer may also be facing thinning have stirred up debate amount the scientific community. Read here to understand more about ozone depletion.
A new ozone hole has been detected over the tropics, at latitudes of 30 degrees South to 30 degrees North, a recent study claimed.
What is the Ozone layer?
The ozone layer is a layer of the stratosphere, the second layer of the Earth’s atmosphere. The stratosphere is the mass of protective gases clinging to our planet.
The Ozone layer is present in Earth’s atmosphere (15-35 km above Earth) in the lower portion of the stratosphere and has relatively high concentrations of ozone (O3).
The ozone layer normally develops when a few kinds of electrical discharge or radiation splits the 2 atoms in an oxygen(O2) molecule, which then independently reunite with other types of molecules to form ozone.
Ozone is only a trace gas in the atmosphere – only about 3 molecules for every 10 million molecules of air.
But it has a very important role: The Ozone layer reduces harmful Ultraviolet (UV) radiation reaching the Earth’s surface. The ozone layer acts as a shield for life on Earth.
UV light can penetrate organisms’ protective layers, like skin, damaging DNA molecules in plants and animals.
There are two major types of UV light: UVB and UVA.
- UVB is the cause of skin conditions like sunburns, and cancers like basal cell carcinoma and squamous cell carcinoma.
- UVA light is even more harmful than UVB, penetrating more deeply and causing deadly skin cancer, melanoma, and premature aging.
The ozone layer, our Earth’s sunscreen, absorbs about 98 percent of this devastating UV light.
Ozone layer depletion
Ozone layer depletion is the gradual thinning of the earth’s ozone layer present in the upper atmosphere.
The thickness of the ozone layer varies immensely on any day and location.
Ozone depletion also consists of a much larger springtime decrease in stratospheric ozone around Earth’s Polar Regions, which is referred to as the ozone hole.
The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants, and foam-blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons).
- ODS have been proven to be eco-friendly, very stable, and non-toxic in the atmosphere below.
- This is why they have gained popularity over the years.
- However, their stability comes at a price; they can float and remain static high up in the stratosphere.
Since the early 1970s, scientists observed a reduction in stratospheric ozone and it was found more prominent in Polar Regions. Ozone Depleting Substances (ODS) have a lifetime of about 100 years.
There are two regions in which the ozone layer has depleted:
- In the mid-latitudes, for example, over Australia, the ozone layer is thinned. This has led to an increase in UV radiation reaching the earth. It is estimated that about 5-9% thickness of the ozone layer has decreased, increasing the risk of human over-exposure to UV radiation owing to the outdoor lifestyle.
- In atmospheric regions over Antarctica, the ozone layer is significantly thinner, especially in the spring season. This has led to the formation of what is called the ‘ozone hole’.
Ozone holes refer to the regions of severely reduced ozone layers. Usually, ozone holes form over the Poles during the onset of the spring seasons.
- One of the largest such holes appears annually over Antarctica between September and November.
There are a few natural causes of ozone depletion are also like Sun-spots and stratospheric winds. But this has been found to cause not more than 1-2% depletion of the ozone layer and the effects are also thought to be only temporary. Major volcanic activity can also contribute to ozone depletion.
Also read: Kyoto Protocol, 1997
Effect of ozone depletion
Ozone layer depletion increases the amount of UVB that reaches the Earth’s surface. Laboratory and epidemiological studies demonstrate that UVB causes:
- non-melanoma skin cancer
- Plays a major role in malignant melanoma development.
- UVB has been linked to the development of cataracts, a clouding of the eye’s lens.
UVB radiation affects the physiological and developmental processes of plants. Despite mechanisms to reduce or repair these effects and an ability to adapt to increased levels of UVB, plant growth can be directly affected by UVB radiation.
Indirect changes caused by UVB:
- changes in plant form
- how nutrients are distributed within the plant
- timing of developmental phases and secondary
- smaller leaf size
- flowering and photosynthesis in plants,
- lower quality crops for humans.
- the decline in plant productivity would in turn affect soil erosion and the carbon cycle.
These changes can have important implications for plant competitive balance, herbivory, plant diseases, and biogeochemical cycles.
On biogeochemical cycles
Increases in UVB radiation could affect terrestrial and aquatic biogeochemical cycles:
- It can alter both sources and sinks of greenhouse and chemically important trace gases (e.g., carbon dioxide, carbon monoxide, carbonyl sulfide, ozone, and possibly other gases).
- These potential changes would contribute to biosphere-atmosphere feedbacks that mitigate or amplify the atmospheric concentrations of these gases.
On marine ecosystems
Phytoplanktons 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.
- UVB radiation has been found to cause damage to the early developmental stages of fish, shrimp, crabs, amphibians, and other marine animals.
- The most severe effects are decreased reproductive capacity and impaired larval development.
- Small increases in UVB exposure could result in population reductions for small marine organisms with implications for the whole marine food chain.
- Synthetic polymers, naturally occurring biopolymers, as well as some other materials of commercial interest are adversely affected by UVB radiation.
- Today’s materials are somewhat protected from UVB by special additives.
- Yet, increases in UVB levels will accelerate their breakdown, limiting the length of time for which they are useful outdoors.
Global efforts to tackle ozone depletion
The global recognition of the destructive potential of CFCs led to the 1987 Montreal Protocol, a treaty phasing out the production of ozone-depleting chemicals. Scientists estimate that about 80 percent of the chlorine (and bromine, which has a similar ozone-depleting effect) in the stratosphere over Antarctica today comes from human, not natural, sources.
In 2016, the Kigali amendment to the Montreal Protocol was agreed upon to reduce the manufacture and use of Hydrofluorocarbons (HFCs) by roughly 80-85% from their respective baselines, till 2045.
- Hydrochlorofluorocarbons are powerful greenhouse gases, but they are not able to deplete ozone.
- This phase down is expected to arrest the global average temperature rise to 0.5o C by 2100.
Everyone should also take steps to prevent the depletion of the ozone layer.
- One should avoid using pesticides and shift to natural methods to get rid of pests instead of chemicals.
- The vehicles emit a large number of greenhouse gases that lead to global warming as well as ozone depletion. Therefore, the use of vehicles should be minimized as much as possible.
- Most cleaning products have chemicals that affect the ozone layer. We should substitute that with eco-friendly products.
- Maintain air conditioners, as their malfunctions cause CFC to escape into the atmosphere.