What is Global Warming?

 The term 'Global Warming' refers to an expected rise in global temperature due to certain human activities. As we know, It is the process which is continuously warming the earth. But why are we so concerned about it? The answer is that our planet's overall temperature in almost every region has been on a rise for over a century now. Changes in climate and temperature have been recorded during the past century. The reason behind this increase in temperature is the continued emission of Carbon Dioxide and other greenhouse gases in the atmosphere which are capable of trapping heat. The most well-known greenhouse gas is Carbon Dioxide. CO2 is transparent to light but absorbs heat. Scientists have estimated the carbon dioxide concentration in our atmosphere has increased about 15% during the past century as a result of fossil fuels, increase in population and deforestation. What is the consequence? The result is that the layer of CO2 so formed over earth absorbs the sun's heat and thus prevents its escape thus causing the green house effect.

What is Green House Effect?

This mechanism by which carbon dioxide traps heat in the atmosphere is referred to as the "greenhouse effect". Carbon dioxide, along with other greenhouse gases, allows the shorter wavelengths of energy radiating from the sun to pass through to the earth's surface and heat it. However, the hot earth emits only the longer wavelengths of energy (infra-red radiation) back into space. The CO2 molecules in the atmosphere absorb these infra-red radiations before it escapes into space and thus a certain amount of heat is retained in earth's atmosphere, providing an additional source of energy (see figure). This heat energy adds to the already passed through energy from the sun and causes a warming effect on the earth. This in turn has many effects. For Example, it increases the average temperature of parts of earth, due to excessive heat the polar ice caps start to melt away causing a rise in sea levels and flooding of many coastal areas of the world. In short, the effects are truly devastating. It is believed that without water vapor, CO2, and other greenhouse gases in the air, the planet's average temperature would be about 34°C cooler on average than it is today.

Figure: The Greenhouse Effect

Why Are We So Worried About This?

The reason behind our worry is that certain human activities are now disturbing the natural balance between the processes that release carbon dioxide into the atmosphere and the processes which remove it. In particular, the burning of fuels such as coal, petroleum and natural gas tends to increase the amount of carbon dioxide in the atmosphere. According to one estimate, the burning of fuels releases about 18000 million tons of carbon dioxide into the atmosphere each year. The destruction of forests to make cultivated fields also decreases the consumption of carbon dioxide by plants, because cultivate fields are less efficient in photosynthesis than forest. This disruption in the balance of Carbon Dioxide released and absorbed has resulted in an alarming increase in the amount of Carbon Dioxide entering the air. This has been happening for a long long time now. As the concentration of CO2 has increased in the earth's atmosphere, so has the temperature. These human activities have increased the amount of carbon dioxide from 0.027% to 0.035% in about one hundred years. It is estimated that, if this trend continues the amount of carbon dioxide will be doubled by the middle of the next century.

Figure: Atmospheric CO2 increase in the past 250 years