Climate change is a fact today. People across the globe experience unusual weather which is in a way manifestation of the global climate change. Rise in the global mean surface air temperature is the most significant sign of the change. There are also signs of melting of glaciers, thinning of ice, sea surface rise, extreme rainfall etc. These changes are alarming and make people very much concerned about the future of the earth. Climate scientists face the challenge of understanding the physical processes involved by analysing the vast amount of available observational data and mathematical modelling.