A thermodynamic model of global warming (greenhouse effect) has been developed to calculate the rise in global temperature and sea level due to increasing concentration of atmospheric greenhouse gases relative to the pre-industrial era (approximate to 1800 AD). The growth rate of various greenhouse gases in future decades has been taken as per IPCC-1996 technical data. Accordingly, the mean global temperature is projected to increase by about 1.9 K during 1800-2100 AD out of which 1.3 K will be in the next 100 years (i.e. twenty first century), Also, the mean sea level is projected to rise by about 86 cm during 1800 to 2100 AD out of which 60 cm will be in the next 100 years. It is the thermal expansion of oceans which accounts for about 95% of the rise in sea level and the rest comes from the melting of ice in greenland, glaciers and mountain caps.