Hi Nitish,

it depends on the question and on the time-scale that you are interested in. But generally, for modelling climate you will have to model at least the physics of the atmopshere and the ocean, possibly also the biogeochemistry, i.e. mainly the carbon cycle on land and in the ocean. A good point to start your reasearch is reading, e.g. the newest report of the working group 1 of the IPCC, which is freely available from http://www.ipcc.ch/

Then, if you want to get practical, you will probably quickly realize that you need a big computer. Most of the models are written in fortran, because that is still the language that you get the best optimizing compilers for. One relatively simple climate model that you can try to run on a PC is cGenie, look at

http://www.seao2.info/mycgenie.html

Here you will find a large amount of tutorial material also.

Hope that helps to get you started,

Christoph

thank you Christoph Voelker

You may also use decision support sytem for agrotechnology transfer. DSSAT. which is available from www.agmip.pk and some other languages like R. and APSIm model also available in the resources portal of agmip.pk website.