Changes in ozone levels have little effect on global temperature:
Ozone has very little direct effect on global temperature, because it lessens incoming solar radiation by almost the same amount as it heats the earth as a greenhouse gas. Of the solar radiation reaching the earth’s surface, UV is only 3% and of that UV-B radiation makes up only 5%. The sun’s total irradiance, about 200 watts per square meter. Therefore, an average depletion of the ozone layer of 3% has a minuscule effect on radiation reaching the earth, about 0.01 watts per square meter. Countering the warming effect of a thinner ozone layer is the cooling effect of less of a greenhouse gas of about 0.015 watts per square meter. Thus, depletion of the ozone layer, neither significantly heats nor cools the planet. The quantity of ozone in the stratosphere, however, does have impact human health.
Increased emissions will thin the ozone layer.
If you search the Internet you will find page after page about refrigerant chemicals and the ozone hole, but very little about emissions and ozone. A bit of science: Both ozone and oxygen reduce UV radiation. Twenty percent of the sun irradiance is ultraviolet radiation. Oxygen, high in the stratosphere, absorbs most of the very harmful UV-C (of very short wavelength),while the ozone in the ozone layer absorbs the great majority of the harmful UV-B that is almost 10% of the sun’s irradiant power and a bit of UVA. Most of less harmless UV-A (near visible light radiation) makes it through the atmosphere to the surface. So, if the ozone layer thins, more UV-B will reach the earth’s surface, effecting the health of animals and plants.
The initial reason to protect the ozone layer of the atmosphere was to shield plants and animals from UV damage. When the “ozone hole” was discovered over the Antarctic, almost every nation banned many uses of long-lasting chlorine and bromine chemicals that destroy ozone. Some chlorine compounds occur naturally, however. They are stable in the troposphere, but when they reach the stratosphere, UV slowly breaks them down. The free chlorine atoms that are produced destroy ozone. This process is vastly accelerated in the Antarctic by very cold (-90ºC) polar winter temperatures that create unusual stratospheric clouds that catalyze chlorine chemical breakdown.
Recently, because the warming of the troposphere (lower atmosphere) is balanced by cooling in the stratosphere, the colder stratosphere is now are causing ozone depletion in winter near the north pole, and even, once as of this writing, a northern ozone hole, while the southern hemisphere ozone hole recovery has slowed.1 2
Since it isn’t intuitively obvious why a warmer troposphere causes a colder stratosphere, think of the layer of air immediately outside a house, assuming it doesn’t mix with the air further away. Heat from the house warms that layer, but if you add more insulation to the house walls, the outside air is heated less — it becomes colder. Water vapor, the most important greenhouse gas, is almost entirely at lower levels of the atmosphere, and other greenhouse gases are more concentrated there, so they act as “insulation” below the stratosphere.
In addition to the effect of emissions in creating a colder stratosphere, increasing nitrous oxide emissions are causing a direct breakdown in the ozone layer. 3
- https://acp.copernicus.org/articles/18/1379/2018/ ↩︎
- https://research.noaa.gov/article/ArtMID/587/ArticleID/2843/Two-additional-regions-of-Asia-were-sources-of-banned-ozone-destroying-chemicals ↩︎
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3306630/ ↩︎