Recently, the NOAA announced that chlorine levels in the
stratosphere have begun to decline, which indicates that the ozone depletion
trend may be curbed. While this is good news for those concerned with skin
cancer and related UV-exposure diseases, this may affect the global warming
problem negatively. Other sources (IPCC) cite that the ozone layer and its
depletion factors have both direct and indirect effects on climate forcing.
In this paper, additional information will be presented that updates and
extends this research. In particular, ozone as a greenhouse gas, CFC's as
greenhouse gases, and indirect radiative forcing by hydroxyl (OH) radicals
will be discussed.
It is known that ozone is a greenhouse gas. It absorbs out-going long-wave radiation. Therefore, a decrease in stratospheric ozone leads to an increase in radiative forcing (global warming). Also, an increase in tropospheric ozone can warm the "troposphere-surface system through increases in absorption of both the solar and long-wave radiation." This also leads to global warming.
It is interesting to note that surface temperatures are more sensitive to ozone changes in the lower stratosphere and upper troposphere. Also, because ozone is not sensitive to mixing, ozone may be more important to regional climate, especially at high and middle latitudes. For these reasons, warming due to an increase in atmospheric ozone will be more local, and less global.
In addition, ozone-depleting chemicals (such as CFC's) contribute to direct radiative forcing. They adsorb out-going long-wave radiation. Therefore, the decrease in radiative forcing by the loss of ozone is somewhat compensated for by an increase in CFC's.
The ozone layer also indirectly affects radiative forcing. In this case, it is assumed that the stratospheric ozone column has been reduced. Then tropospheric ozone can react with water and ultraviolet light (lE310 nm). This reaction forms two hydroxyl radicals (OH) and oxygen gas. Hydroxyl radicals react with sulfur dioxide (SO2) to form sulfuric acid (H2SO4). Sulfuric acid increases the concentration of cloud condensation nuclei. This increases albedo due to cloud formation. This, in turn, decreases radiation forcing. So, ozone depletion leads to a global cooling situation.
In addition, since hydroxyl radicals are a sink for methane and carbon monoxide, and increase in hydroxyl radical with lead to a decrease in methane and carbon monoxide concentrations. This was discovered when TOMS data showed that stratospheric ozone depletion was at an all-time low in 1991. At the same time, the growth rates of methane and carbon monoxide were lower than expected. Since methane and carbon monoxide are greenhouse gases, this lead to a decrease in radiative forcing, and a global cooling situation.
In this paper, the effects of the ozone layer and its depletion were discussed. Because of the complex relationships between ozone layer depletion and radiative forcing, this relationship has not yet been quantified. Although much research has been done on this subject, much more most still be done to be able to predict the influence of ozone depletion on global climate changes.
References
Houghton, J. T., Jenkins, G. J., Ephraums, J. J., ed., 1993: Climate Change--The IPCC Scientific Assessment. Cambridge University Press 49-51.
Wang, W.-C., Liang, X.-Z., Dudek, M. P., Pollard, D., Thompson, S. L., 1995: Atmosphere Ozone as a Climate Gas. Atmospheric Research, 37, 247-256.
Ramaswamy, V., Schwarzkopy, M. D. and Shine, K. P., 1992: Nature 355 810-812.
Toumi, R., Bekki, S., Law, K. S., 1992: Indirect Influence of Ozone Depletion on Climate Forcing by Clouds. Nature 372, 348-351.
Bekki, S., Law, K. S., Pyle, J. A., 1994: Effect of Ozone Depletion on Atmospheric CH4 and CO Concentrations. Nature, 371, 595-597.