The earth is heated up by sunlight and some of the heat that is absorbed by the earth is radiated back into space. However, some of the gases (like C02) in the lower atmosphere, serving like glass in a green house, allow the solar radiations, but do not allow the earth to re-radiate the heat into space.
The sun-rays consist of U.V., visible, and infrared radiations. The ozone layer absorbs most of the UV radiation and allows visible and IR radiations to pass through towards the earth. Since IR rays are of short wavelength, so they easily pass through the C02 layer in the atmosphere.
These infrared rays cause heating effect to the objects on the earth and atmosphere on the earth. Consequently, if large amount of carbon dioxide is present in atmosphere, it causes more heating up of the earth’s atmosphere. Hence, the temperature of the earth’s atmosphere rises.
CO? is released by volcanoes, oceans, decaying plants as well as human activities, such as deforestation and combustion of fossil fuels. Other gases that are responsible for green house effect are water vapour, methane and chlorofluorocarbons (CFC’s). Chlorofluorocarbons (CFC’s) are generally used as coolants in refrigerators, propellants in aerosol sprays and plastic foam materials like Thermocoles. Methane (CH4) is released from coal mines, rice paddy cultivation; decomposition of organic matter in sv/amps and guts of terminates in forest debris. Every year the world wide concentration of C02 is increasing at a rate of 0.75 ppm, causing an increase in the temperature at a rate of 005°C per year. Green house gases (especially CO? and water vapour) are mainly responsible for keeping our planet warm and thus sustaining life on the earth.
Effects of Global Warming
Although accurate forecasting of global warming effects is still to be evolved, some of the possible changes owing to global warming are listed here, which are again predictions.
(i) Hydrological cycles will intensity, and as a result the rate of precipitation and evaporation will accelerate.
(ii) An increase in precipitation of about 2 to 0.5% per 1° Celsius of temperature increase. However, it is evident now that the frequency of intense precipitation has increased during the last few decades in some regions.
(iii) A remarkable change in sea level is expected. A minimum increase of 50 to 25 cm by the end of 2100 A.D., therefore frequent floods as well as submergence of most low lying areas like Bangladesh and Maldives
(iv) Decrease in soil moisture is due to increase in summer temperature. As a result, occurrence of drought will be frequent.
(v) The upper layers of the atmosphere, i.e., stratosphere will continue to cool owing to more accumulation of CO, at lower atmosphere level.
(vi) India and Bangladesh both will be battered by typhoons and flooding.
(vii) Marginal farmland in Central China may get more rain thus improvement in yields.
(viii) Farming will be seriously affected during hotter and their summer in Midwestern USA.
Following changes will have greater impact on weather, food production, and the economy:
1. Extreme weather related events like, cyclones, floods, droughts, hailstorms etc. will bring down crop production.
2. Frequent environmental damages due to extreme weather events in recent decades have been noted by the insurance industry especially in case of Caribbean and the Pacific regions. Here the insurance premiums have gone up with the consequence that a few can afford to pay for insurance.
3. In case of Great Lakes in US which is one of the busiest waterways in the world for transporting iron ore, grains, limestone’s, coals etc. may remain free from ice for 11 months against 8.5 months at present.
4. The temperature increase and possible increase in precipitation at higher latitudes would benefit Canada to grow more wheat from current production level, whereas US will lose its wheat production to Canada owing to high probability of extreme heat waves. Therefore, Canada will export more wheat to developing countries than US.
5. Africa may benefit, at least in rainfall. The shifting of trade winds or rain belt across the equator will shift northward. Thereby, most affected drought areas like Chad, Sudan and Ethiopia will get more rains which will enable them to grow crops in volume.
6. The new generation secondary goods which will be free from CFCs and other green house gases may tend to capture the markets of developing countries. While for developing countries production of such goods will be difficult due to strict patent laws which will present the passage of technology know-how neither free nor at subsidized price to developing countries.
7. One of the biotic effects will be the rapid destruction of forests without its replacement. Rising temperature could convert fertile belts of North America and the Mediterranean into arid regions.
8. Through the effect of green house gases will be global its impact on Asia, Africa and Latin America will be greater on account of weaker technologies and infrastructural base, greater dependence on primary natural resources and lack of financial resources necessary to mitigate the effect on agriculture and fragile coastal ecosystems. As a result, in India, rice production in high yield areas of Punjab and Haryana will be reduced by 0.75 tonnes per hectare while wheat production would decline by 10%.