Global records of earth’s surface temperatures indicate that a warming of about 0.5° (0.3°-0.7°C) has occurred during the last century alone. Results from recent climatic models suggest that mean global temperatures shall rise by 2°-6°C during the next century if we assume that carbon dioxide concentration in the troposphere increases to 600 ppm.
The projected change in mean surface temperatures may appear insignificant because variations of this magnitude are experienced in course of seasonal or even daily weather. In fact this is not so. During the last great Ice Age, about 12,000 years ago, when much of Northern America and Europe was covered with a sheet of ice, the mean surface temperatures were only about 5°C lower than today.
The world climate was very much different from what it is now. The transition from the great Ice Age to present- day climate during which average surface temperature rose by 5°C took almost twelve thousand years. But the variations of almost similar magnitude shall be experienced within a course of single century if greenhouse gases continue to rise at the present rate.
Though there are considerable uncertainties regarding the precise consequences of global warming one of the obvious results of the general heating up of earth’s surface shall be a rather rapid rise in mean sea level.
During the last fifteen thousand years mean sea level has slowly been rising. Evidences suggest that about 12,000 years back it was nearly 100 m lower than the present-day level. It is expected that global rise in temperatures shall further enhance the rate of already rising sea levels in two ways.
Firstly, large deposits of ice present on earth’s surface shall melt which will add more layers of water. An increase of 4°-5°C could cause enough expansion of this enormous mass of water so as to raise the mean sea level 5-6 cms.
If all ice present on earth’s crust was to melt, sea level could rise by about 60 m. large stretches of low lying areas shall be submerged. As much of the world population live near shore, this could be a total catastrophe. About sixty odd island countries shall face deep encroachments by sea water and some like Maldives may disappear altogether.