Ozone Depletion and the Greenhouse Effect
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Ozone Depletion
Ozone depletion is a steady decline of about 4 percent in the total amount of ozone in Earth's stratosphere. There is also a much larger springtime decrease in the stratospheric ozone around Earth's polar regions. The latter phenomenon is referred to as the ozone hole.
Causes of Ozone Depletion
The main cause of the ozone hole is man-made chemicals, especially man-made halocarbon refrigerants, solvents, propellants, and foam-blowing agents (CFCs, HCFS, halons). These compounds are transported into the stratosphere by wind. Once in the stratosphere, they release halogen atoms through photodissociation, which catalyze the breakdown of ozone (O3) into oxygen (O2).[3] Both types of ozone depletion were observed to increase as emissions of halocarbons increased.
Effects of Ozone Depletion
Ozone depletion and the ozone hole have generated worldwide concern over increased cancer risks and other negative effects. The ozone layer prevents most harmful UVB wavelengths of ultraviolet light (UV light) from passing through the Earth's atmosphere. These wavelengths cause skin cancer, sunburn, and cataracts, which were projected to increase dramatically as a result of thinning ozone, as well as harming plants and animals.
The Montreal Protocol
These concerns led to the adoption of the Montreal Protocol in 1987, which bans the production of CFCs, halons, and other ozone-depleting chemicals.
The Greenhouse Effect
The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without its atmosphere.[1][2]
How it Works
If a planet's atmosphere contains radiatively active gases (i.e., greenhouse gases) they will radiate energy in all directions. Part of this radiation is directed towards the surface, warming it.[3] The intensity of the downward radiation - that is, the strength of the greenhouse effect - will depend on the atmosphere's temperature and on the amount of greenhouse gases that the atmosphere contains.
The Greenhouse Effect on Earth
Earth's natural greenhouse effect is critical to supporting life. Human activities, mainly the burning of fossil fuels and clearing of forests, have strengthened the greenhouse effect and caused global warming.[4]
The Greenhouse Analogy
The term "greenhouse effect" arose from a faulty analogy with the effect of sunlight passing through glass and warming a greenhouse. The way a greenhouse retains heat is fundamentally different, as a greenhouse works mostly by reducing airflow so that warm air is kept inside.