Here are two neat online climate-related calculation systems:
The first is provided by the American Environmental Protection Agency and allows for various kinds of conversions. You can work out what a volume of one greenhouse gas would be equivalent to in another gas; you can also look at a set quantity of carbon dioxide emissions as being equivalent to certain number of barrels of oil, homes heated for a year, etc.
The second site – RoofRay – lets you draw solar panels on top of buildings using the satellite photos in Google Maps. It then tells you how much it would cost to cover that area with panels, how much energy it would produce, and how long the system would take to pay off its own costs.