This summer, which people feel the most miserable in the recent past as high daytime temperature is being recorded, is a significant indicator for understanding the climate change. It is all due to global warming, said a professor of geology in Andhra University, N. Subba Rao, on the eve of World Environment Day being observed on Tuesday. “Thoughtless and greedy destruction of environment over the last many decades is having its effect now.”

According to the professor, global warming is caused by the rising average temperature of earth's surface and oceans due to effect of greenhouse gases like water vapour, which causes 36 to 70 per cent of the greenhouse effect; carbon dioxide (nine to 26 per cent), methane (four to nine per cent) and ozone (three to seven percent).

Even slight increases in atmosphere levels of carbon dioxide, which tends to remain in the atmosphere for hundreds of years, can cause a substantial increase in temperature, as it absorbs and emits infrared radiation. CO2 is for photosynthesis, a process during which oxygen is released by the plant by absorbing CO2. But photosynthesis is not taking place actively due to deforestation and carbon dioxide content in the atmosphere is increasing.

Its increase began in 1800 due to deforestation and reached significant level as early as 1900 due to industrial revolution adding to deforestation. Most of the conditions that increased warm conditions are due to human activities like combustion of fossil fuels, transportation, heating, manufacture of cement (which releases 22 billon tons of CO2 into atmosphere every year. A passenger vehicle produces 5.2 tons of CO2 a year on an average.

During 21st century, the global surface temperature is likely to rise by 1.1 to 2.9 degree C for the lowest emission scenario and 2.4 to 6.4 degrees C for the highest one. Since 1979, the land temperatures have increased about twice as fast as ocean temperatures. Ocean temperatures increase more slowly than land temperatures because the ocean loses more heat by evaporation. Global temperature will rise likely by about 1 to 3.5 degree C by the year 2100. The main global warming impacts are rising of sea levels, change in amount and pattern of rainfall causing droughts and fires in some areas, and floods in other areas; increased likelihood of extreme events like floods, hurricanes, etc; change in crop yields; melting of ice caps near poles; melting of glaciers; loss of animal population on a large scale; spread of diseases; bleaching of coral reefs due to warming seas and acidification due to carbonic acid formation, and loss of plankton due to warming seas. By 2080, crop yields in developing countries could decrease by 10 per cent to 25 per cent on average, while India could see a drop of 30 per cent to 40 per cent.

India has a total forest area of about 76.29 million hectares and Andhra Pradesh accounts for the giant chunk of decrease in forest area and if steps are not initiated immediately the forest area in the State could drop down to 18 per cent by end of next year.

Much thought must be given to using renewable sources of energy like solar, wind, wave, etc. to reduce burning of fossil fuels and thereby the global warming.