Modeling and calculating earth’s climate, with the many parameters involved (sun, atmosphere, land, water, snow/ice, etc.), used to be the exclusive domain of supercomputers, and still is for the most complicated models. But there’s a simplified computer climate model available for free for both Windows and Macintosh that lets you run climate models on a desktop PC, and allows you to investigate both past and future climatic scenarios.
The Educational Global Climate Model (EdGCM) software is created and distributed by Columbia University. It lets you input parameters related to the atmosphere (e.g. CO2 concentrations), oceans, land surface, solar forcing, orbital factors, and others, and then run a simulation to show how the climate changes with time. It takes some time to run a simulation – about 100 years of simulated time takes about a day on a modern PC – so it’s the sort of thing you’d start up and then let run for a while by itself. It comes with sample scenarios to start out with, like doubling CO2 instantly, looking at the last ice age 21,000 years ago, even “Snowball Earth”, the period about 700 million years ago when some scientists believe the Earth was covered in ice and snow from the poles to the Equator.
The EdGCM outputs only numerical data, but the companion EVA program can create plots and maps of the results:
The latest version of EVA can create KML files, letting you overlay the results on top of the globe in Google Earth.
The program is somewhat technical, so learning and running it will take some time. But the website includes links to the manual, workbooks, exercises, video tutorials, discussion forums, wikis, exchanges for swapping simulation scenarios, etc., to help with the learning process.