Pollution counters global warming

IF it were not for the widespread pollution caused by human beings, global warming caused by green- house gases like carbon dioxide and methane would have made the earth a lot warmer than it is. The world is thus in a bind: reduce pollution and save the ozone layer, but then suffer global warming.

The latest report of the United Nation's Intergovernmental Panel on Climate Change (IPCC) claims that the destruction of the ozone layer has been cooling the earth. In fact, it appears that the cooling effect of the ozone hole created by the accumulation of chlorofluoro-carbons (CFCs) in the atmosphere is effectively counteracting the heating effect of the CFCs.

The report explains that the stratosphere gets heated as the ozone layer absorbs ultraviolet radiation. The stratosphere then emits infrared radiation which warms the atmosphere below. Thus, as stratospheric ozone decreases and the ozone hole grows,'less ultraviolet radiation gets. absorbed. More of this light reaches the earth's surface making it warmer. But as less ultraviolet radiation is absorbed in the stratosphere, the stratosphere itself cools and emits less infrared radiation and contributes to global cooling.

Sulphur dioxide is another polluting gas generated when fossil fuels burn. Sulphur dioxide reacts in the atmosphere to form tiny droplets of sulphate aerosols. Sulphur particles and other aerosols cool the earth by reflecting back the sun's rays. The sulphate aerosols also form cloud condensation nuclei which alter the albedo effect of the clouds, that is, their ability to reflect sunlight. The IPCC report points out that the cooling effect of these sulphate aerosols on the earth's surface is quite high. The quantity of sulphur emissions generated by human beings in the southern hemisphere is much less and, hence, little compensatory cooling has taken place there.