Global Environmental Changes Introduction

The atmosphere resource of our world is unique and available to our planet only. No other planet is found to have similar atmosphere. Earth's atmosphere is a legacy from history of this planet. It was formed billions of years back. In the formative years, as the earth started cooling, it did not have free oxygen (theory of chemical evolution by Oparin and Haldane). The atmosphere, lithosphere and hydrosphere were not clearly distinguishable. As micromolecules and macromolecules of C, H, N and O compounds like, glycerol, fat, pyrimidines, polysaccharide, lipid, proteins, nucleic acids were formed, the life forms originated.

Now clear distinctions of characteristic layers of earth's cover can be identified. They are atmosphere, stratosphere, ionosphere. Atmosphere spreading to 200 km from earth has specific characters of its own. Such characters include the varying chemical composition of air according to distance from earth's surface, decreasing pressure with altitude, differential ability to filter the sun's radiation etc.

Earth's atmosphere in its present form, is evolved and even now being influenced by earth's movement on its axis as well as sunlight. These two parameters decide what type of atmosphere we have now - its composition as well as the total height of atmospheric cover around the earth. Such an atmosphere is a dynamic coverage of earth - with modification in its composition, presence and nature of atmosphere. But, these modifications have set in a larger time scale of millions of years. Therefore, millions of years back, we had an atmosphere not exactly similar to what we have now. Moreover atmosphere cannot remain the same after 1-2 million of years. The environmental changes in atmosphere are a part of such modifications.

Several evidences have shown past environmental changes. Even in a short span of 100 - 1000 years, the rainfall, sunlight has changed, extent of river flow has changed and vegetation and its characters have changed. Important difference in present day situation as compared to earlier situation is population. Unlike animal population dominating world, say a million year ago, we have human population dominating the world today. Less heartening is the fact that human population has proved to be more nature - damaging species than animal population. Human population, which is overcrowded in the last 100 years, is responsible for several activities causing damage to atmospheric characters. Such damaging activities are modifying our atmosphere offering some quickly self destroying path.