The ill-famed ozone hole is basically an area of the ozone layer, above Antarctica, which is subjected to seasonal depletion on a large scale. The depletion can be basically divided into two parts: (i) depletion of around 4 percent per decade in the stratosphere and (ii) rapid depletion of the stratospheric ozone at the poles. The phenomenon triggered by the emission of harmful compounds, such as the chlorofluorocarbons, halons, and carbon tetrachloride, has been going on since 1970s. It has caused a significant damage to the ozone layer, especially at the poles.
An Introduction to the Ozone Layer
The Earth's atmosphere is divided into five layers: the troposphere, stratosphere, mesosphere, thermosphere, and the exosphere. Lying between the troposphere and mesosphere, the stratosphere extends over a vertical distance of 32 miles. The ozone layer is a part of the stratosphere and ranges between 8.07 miles to 20.42 miles. This layer contains ozone―a form of oxygen with three molecules as opposed to normal oxygen with two molecules. These molecules absorb the harmful ultraviolet radiations coming from the Sun, which have the ability to harm the lifeforms on the Earth.
How is the Ozone Layer Getting Depleted?
The factors responsible for depletion of the ozone layer include various compounds released in the Earth's atmosphere as a result of human activities. These include chlorofluorocarbons, halons, etc., which rise in the air, reach the stratosphere, and destroy the ozone molecules through a series of chemical reactions. The rate at which this depletion is happening is relatively faster at the poles.
Of the various theories about the depletion of this layer, one in particular suggests that the rate of depletion is faster at the poles because of the fall in temperature of stratosphere. Studies have revealed that this fall in the temperature is making the ozone layer vulnerable to the damage caused by emissions of these harmful compounds. Other than the low temperature in polar areas, the fact that the greenhouse gases are trapping the Sun's radiation within the troposphere is also contributing to the fall in temperature of stratosphere and making the ozone layer vulnerable to depletion.
The ozone layer in this region has been depleted by 33 percent compared to what it was in the 1970s. More recently, the World Meteorological Organization (WMO) revealed that the ozone layer hole has become bigger; now measuring 11 million square miles. This report was based on the studies conducted by the National Aeronautics and Space Administration (NASA). The Montreal Protocol―an international agreement to phase out the use of harmful compounds that damage the ozone layer―did help in curbing the damage to some extent, but recent studies reveal that the depletion of this layer continues even today.
The rate at which the ozone hole is increasing is a sign of approaching calamity which has put the scientific fraternity on its toes. All this while, it was assumed that we had dealt with the problem by implementing the Montreal Protocol. More recently, however, the relationship between the ozone depletion and global warming has surfaced as an entirely new concern. If all the provisions of the Montreal Protocol are followed by the 196 countries which ratified it, then the ozone layer should recover by 2050.
However, if the recent trends suggesting that global warming is indirectly affecting the ozone layer depletion are true, then it wouldn't be surprising to see the recovery period extended considerably.