1.4.2. Global Warming

In very cold regions, glass houses are constructed for growing vegetables. These are known as Greenhouses. In these houses, glass covering allows short wavelength sunrays to enter but does not allow it to be radiated back to atmosphere. At atmospheric level, the greenhouse gases do not allow thermal radiation from a planetary surface (long waves) to pass and re- radiate them in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases. Major greenhouse gases are: carbon dioxide, methane, nitrous oxide, water vapour and Ozone.

With increase in the percentage of greenhouse gases, it is believed that temperature of earth is increasing dramatically. This is termed as global warming. Main contributor for this rise in temperature is carbon dioxide (CO2). The scientists have observed that CO2 is largely contributed from burning of fossil fuels. The burning of fossil fuels and extensive clearing of native forests has contributed to a 40% increase in the atmospheric concentration of carbon dioxide, from 280 to 392 parts per million (ppm) in 2012.

Other gases such as Methane, water vapour, Nitrous oxide, Hydroflurocarbons (HFCs), Perflurocarbons (PFCs), Sulphur hexafluoride (SF6) are playing considerable role in global warming. SF6, PFCs etc. are present only in traces but their life span and greenhouse potency is very high. For instance, SF6 is the most potent greenhouse gas in existence. With a global warming potential 23,900 times greater than carbon dioxide, one pound of SF6 has the same global warming impact of 11 tons of carbon dioxide. It is also very persistent in the atmosphere with a lifetime of 3,200 years. SF6 is widely used in circuit breakers, gas-insulated substations, and other switchgear to manage the high voltages.

Global warming would adversely affect the ecosystem on the Earth and the weather patterns around the world in the following ways:

♤ Melting of ice at polar regions and glaciers on high mountains. It would increase the sea level.

♤ Many climatic and weather events are expected to change drastically. Recent examples of extreme temperature, precipitation are associated with the global warming.

♤ Global warming would change the habitats of organism. Those unable to adjust to these rapid changes may not be able to survive.