These organisations already fly on green seats:

It is impossible to imagine our international world without air travel. These flights, however, contribute to climate change through the emission of CO2 and other greenhouse gases. GreenSeat helps travel agents and travellers to neutralise the emissions from kilometres flown by investing in climate projects. More and more travel organisations offer the GreenSeat option during their booking procedure, allowing travellers to choose a Green Seat with just a single click of the mouse!

CO2 reducing projects: