Hello again. I thought I'd post another climate change idea I don't have time to try :)
Carbon calculators. There are a lot of these out there, but how about one specifically for travel. You put in flights, or journey details, it calculates carbon emissions, then you can pay to offset, choosing from a selection of accredited offset schemes. Carbon Footprint already do something along these lines, but I feel like there's room for more. The calculations themselves are non-trivial, especially if you want to be as accurate as possible, but this seems doable. This could work for individuals or businesses - I could see businesses wanting to offset (air) travel to improve their green credentials.