Greenhouse effect:
Scientists have reason to believe that air pollution. both due to carbon particles or soot and carbon dioxide would affect weather. A rise in surface temperature of land and water due to, what is called. the greenhouse effect is predicted. When sun's rays fall on the atmosphere containing carbon dioxide, some of the heat is reflected towards the sky but much of it passes down to the earth.
Heat from the earth enters the atmosphere and some of it is again reflected back to the earth, while the rest passes through the atmosphere. Thus, the surface of the earth. i.e.. the surface of land and water are net gainers of heat during the day. and this establishes a certain temperature on the surface of the eanh. If the amount of carbon dioxide in the air increased. the net gain of heat and hence temperature on the earth would be greater. The earth would warm up in such a case. A greenhouse is a glass house often used in cold weather to grow plants of warmer climates and it works on the same principle.
The greenhouse has glass walls, and the glass prevents all the heat inside the house from being lost to the atmosphere. You would, perhaps, have experienced the inside of a closed car parked in the sun becoming unbearably hot. The reason is the same. Since 1958. the concentration of carbon dioxide in the atmosphere has risen by almost 6 per cent and is expected to increase in future. What leads to the increase in carbon dioxide level in the atmosphere? VJe shall discuss that now. You have already studied in Unit 14, that plants take up carbon dioxide and use it for making food. Forests comprising of enormous vegetation remove a lot of carbon dioxide from the air. The destruction of forests significantly increases the proportion of carbon dioxide in the atmosphere.
The buming of fossil fuel by industry and transport vehicles also keeps adding carbon dioxide to the air. Thus, there is a continual build up of carbon dioxide in the atmosphere. If the present trend continues, it is feared that a doubling of atmospheric carbon dioxide could occur sometime towards the middle of the next century, and this would cause an average annual temperature rise of 3 to 8OC. This rise in temperature could have a disastrous impact on all life.
It will affect agriculture, resulting in problems in the availability of food and other agriculture- based activities. Melting of polar ice would result in the rise of sea level. This could submerge many coastal areas and farmlands. It is feared that cities like London, Glasgow, Florida, Tokyo, Osaka, Montreal, Stockholm, Copenhagen and Calcutta would loose much of their temtory to the rising waters.