(Kim, et al., “Global Warming: Definition”).
Emission of green house gases as a result of human activity is one the major causes of global warming. The green house gases reabsorb heat from the Earth’s surface, thus trapping the heat in the atmosphere. This process is essential for life to exist on Earth because it plays an important role in regulating the atmospheric temperature. These gases however prevent the additional thermal radiation from leaving the Earth thereby trapping the excess heat. (Stanford Solar Center, “What is it?”)
Earth has undergone climatic changes in the past also but that was not dependent on the activities of mankind. This information is revealed from the evidences left by tree rings, layers of ice in glaciers, sediments under the ocean, coral reefs and sedimentary rocks. As the Earth moved out of the ice ages during the past million years, global temperatures rose from 4 to 7 degree C over about 5000 years. In the last century alone, the temperature has risen 0.7 degree C which is ten times faster than the average rate of warming during the ice age recovery stage. Models have predicted that by the next century temperatures will raise by about 2 to 6 degree C. Previously when global warming took place, it had taken 5000 years for the Earth to warm 5 degrees. The predicted rate of warming for the next five years is 20 times faster. This is an extremely unusual and alarming situation. (Earth Observatory, “How is Today’s Warming Different from the Past?”).
The 21st century might witness an average increase in global temperatures by 1.4 to 5.8 degree C. The number though sounds very small but it can cause significant change in climate conditions. Surprisingly the difference in temperatures of the Earth during the ice age and the non ice age was only 5 degree C. This will not only result in more number of hot days but will also lead to changes in rainfalls and weather conditions.