The results so far

BP Global Choice™ has already offset greenhouse gas emissions in Australia over 2 million tonnes , equivalent to taking 400,000 cars off the road annually.

It's hard to imagine 2 million tonnes of CO2 in the atmosphere, but as one hot-air balloon of 10m diameter contains about a tonne of hot air - imagine seeing 2 million hot-air balloons floating over Australia - that's a lot of balloons!