Discuss the consequences of global warming and ozone layer depletion.

Explanation

(a) Effect of global warming:
Global warming, a consequence of higher concentration of greenhouse gases, has the potential to affect weather and climate, stratosphere and thermosphere, rise in sea level, species distribution and food production.
1. Weather and climate : Global mean temperature rose by` 0-6^(@) C` during the 20th century. It is going to increase further by `14^(@)` - `5-8^(@)C`between 1990 - 2100 AD.
2. Stratosphere and thermosphere :
Warming of troposphere will cause cooling of stratosphere and thermosphere. The whole atmosphere will shrink. Cooling of the stratosphere will increase the size of ozone holes and thinning of ozone shields at other places. Cooling of the thermosphere will disrupt communications and the shielding effect of ionosphere. 3. Sea level change : It is believed that sea level has risen by 15cm during the 20th century, a rise of 1-2 mm every year. By the year 2100 AD, the global mean sea level is going to rise by 0-88m over that of 1990 sea level. Rise in sea level is due to thermal expansion of oceans as the temperature rises, melting of glaciers and Greenland Ice sheets.
4. Range of species distribution : Each species has a particular range of temperature. Global warming will push tropics into temperate areas and temperate - areas towards poles and higher altitudes in mountains A rise of` 2^(@)`-`5^(@)C` can cause pushing of temperate range vegetation some 250-600km towards the pole.
5. Food production : Rise in global temperature is going to have a negative impact on food production despite beneficial effects of Co, fertilization. The various reasons are an increase in basal rate of respiration by plants.
• Lesser storage of food and hence less productivity. Explosive growth of weeds.
• Higher incidence of pathogens and pests.
• Increased evaporation of soil water and higher transpiration from plants resulting in water deficiency. (b) Effects of ozone depletion : Thinning of ozone layer and development of ozone holes increases the amount of UVB radiations reaching the earth.s surface. A 5% ozone depletion increases UV-B radiations by 10%. Increased incidence of UV-B radiations on earth will have the following adverse effects.
Skin Cancers : There is an increase in the incidence of skin cancers. 1% fall in ozone concentration increases UV load of earth by 2% that causes addition of 50,000 cases of skin cancer. In Australia which lies near the area of ozone hole, every second middle aged person suffers from skin cancer while in old persons the incidence is nearly 100%.
Blinding : Many land animals would lose their eyesight and become blind. In human beings the cases of photo-burning, cataract and dimming of eyesight are on the increase. 1% fall of ozone concentration in the stratosphere will blind another 1 lakh persons. Immune System: It is partially suppressed. Incidence of herpes and other immune system related diseases are likely to increase
Larval Stages : More larvae and young ones of aquatic animals will die.
Photosynthesis : Photosynthetic machinery is impaired. Photosynthesis decreases by 10-25%. There is a corresponding fall in the yield of crops.
Nucleic Acids : UV radiation damages nucleic acids by forming dimers. Incidence of harmful mutations increases. 
Phytoplankton : Both photosynthetic activity as well as function of phytoplankton are disturbed by UV-radiations. 6-22% fall in productivity will occur.
Global Warming: Decreased primary productivity over land and inside oceans will increase carbon dioxide concentration resulting in global warming, despite reduction in `CO_(2)`emissions from industries and automobiles.